Disruptor—3.核心源码实现分析
大纲
1.Disruptor的生产者源码分析
2.Disruptor的消费者源码分析
3.Disruptor的WaitStrategy等待策略分析
4.Disruptor的高性能原因
5.Disruptor高性能之数据结构(内存预加载机制)
6.Disruptor高性能之内核(使用单线程写)
7.Disruptor高性能之系统内存优化(内存屏障)
8.Disruptor高性能之系统缓存优化(消除伪共享)
9.Disruptor高性能之序号获取优化(自旋 + CAS)
1.Disruptor的生产者源码分析
(1)通过Sequence序号发布消息
(2)通过Translator事件转换器发布消息
(1)通过Sequence序号发布消息
生产者可以先从RingBuffer中获取一个可用的Sequence序号，然后再根据该Sequence序号从RingBuffer的环形数组中获取对应的元素，接着对该元素进行赋值替换，最后调用RingBuffer的publish()方法设置当前生产者的Sequence序号来完成事件消息的发布。
//注意：这里使用的版本是3.4.4
//单生产者单消费者的使用示例
public class Main {
public static void main(String[] args) {
//参数准备
OrderEventFactory orderEventFactory = new OrderEventFactory();
int ringBufferSize = 4;
ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
//参数一：eventFactory，消息(Event)工厂对象
//参数二：ringBufferSize，容器的长度
//参数三：executor，线程池(建议使用自定义线程池)，RejectedExecutionHandler
//参数四：ProducerType，单生产者还是多生产者
//参数五：waitStrategy，等待策略
//1.实例化Disruptor对象
Disruptor<OrderEvent> disruptor = new Disruptor<OrderEvent>(
orderEventFactory,
ringBufferSize,
executor,
ProducerType.SINGLE,
new BlockingWaitStrategy()
);
//2.添加Event处理器，用于处理事件
//也就是构建Disruptor与消费者的一个关联关系
disruptor.handleEventsWith(new OrderEventHandler());
//3.启动Disruptor
disruptor.start();
//4.获取实际存储数据的容器: RingBuffer
RingBuffer<OrderEvent> ringBuffer = disruptor.getRingBuffer();
OrderEventProducer producer = new OrderEventProducer(ringBuffer);
ByteBuffer bb = ByteBuffer.allocate(8);
for (long i = 0; i < 5; i++) {
bb.putLong(0, i);
//向容器中投递数据
producer.sendData(bb);
}
disruptor.shutdown();
executor.shutdown();
}
}
public class OrderEventProducer {
private RingBuffer<OrderEvent> ringBuffer;
public OrderEventProducer(RingBuffer<OrderEvent> ringBuffer) {
this.ringBuffer = ringBuffer;
}
public void sendData(ByteBuffer data) {
//1.在生产者发送消息时, 首先需要从ringBuffer里获取一个可用的序号
long sequence = ringBuffer.next();
try {
//2.根据这个序号, 找到具体的"OrderEvent"元素
//注意：此时获取的OrderEvent对象是一个没有被赋值的"空对象"
OrderEvent event = ringBuffer.get(sequence);
//3.进行实际的赋值处理
event.setValue(data.getLong(0));
} finally {
//4.提交发布操作
ringBuffer.publish(sequence);
}
}
}
public class OrderEventHandler implements EventHandler<OrderEvent> {
public void onEvent(OrderEvent event, long sequence, boolean endOfBatch) throws Exception {
Thread.sleep(1000);
System.err.println("消费者: " + event.getValue());
}
}
//多生产者多消费者的使用示例
public class Main {
public static void main(String[] args) throws InterruptedException {
//1.创建RingBuffer
RingBuffer<Order> ringBuffer = RingBuffer.create(
ProducerType.MULTI,//多生产者
new EventFactory<Order>() {
public Order newInstance() {
return new Order();
}
},
1024 * 1024,
new YieldingWaitStrategy()
);
//2.通过ringBuffer创建一个屏障
SequenceBarrier sequenceBarrier = ringBuffer.newBarrier();
//3.创建消费者数组，每个消费者Consumer都需要实现WorkHandler接口
Consumer[] consumers = new Consumer[10];
for (int i = 0; i < consumers.length; i++) {
consumers[i] = new Consumer("C" + i);
}
//4.构建多消费者工作池WorkerPool，因为多消费者模式下需要使用WorkerPool
WorkerPool<Order> workerPool = new WorkerPool<Order>(
ringBuffer,
sequenceBarrier,
new EventExceptionHandler(),
consumers
);
//5.设置多个消费者的sequence序号，用于单独统计每个消费者的消费进度, 并且设置到RingBuffer中
ringBuffer.addGatingSequences(workerPool.getWorkerSequences());
//6.启动workerPool
workerPool.start(Executors.newFixedThreadPool(5));
final CountDownLatch latch = new CountDownLatch(1);
for (int i = 0; i < 100; i++) {
final Producer producer = new Producer(ringBuffer);
new Thread(new Runnable() {
public void run() {
try {
latch.await();
} catch (Exception e) {
e.printStackTrace();
}
for (int j = 0; j < 100; j++) {
producer.sendData(UUID.randomUUID().toString());
}
}
}).start();
}
Thread.sleep(2000);
System.err.println("----------线程创建完毕，开始生产数据----------");
latch.countDown();
Thread.sleep(10000);
System.err.println("任务总数:" + consumers[2].getCount());
}
}
public class Producer {
private RingBuffer<Order> ringBuffer;
public Producer(RingBuffer<Order> ringBuffer) {
this.ringBuffer = ringBuffer;
}
public void sendData(String uuid) {
//1.在生产者发送消息时, 首先需要从ringBuffer里获取一个可用的序号
long sequence = ringBuffer.next();
try {
//2.根据这个序号, 找到具体的"Order"元素
//注意：此时获取的Order对象是一个没有被赋值的"空对象"
Order order = ringBuffer.get(sequence);
//3.进行实际的赋值处理
order.setId(uuid);
} finally {
//4.提交发布操作
ringBuffer.publish(sequence);
}
}
}
public class Consumer implements WorkHandler<Order> {
private static AtomicInteger count = new AtomicInteger(0);
private String consumerId;
private Random random = new Random();
public Consumer(String consumerId) {
this.consumerId = consumerId;
}
public void onEvent(Order event) throws Exception {
Thread.sleep(1 * random.nextInt(5));
System.err.println("当前消费者: " + this.consumerId + ", 消费信息ID: " + event.getId());
count.incrementAndGet();
}
public int getCount() {
return count.get();
}
}
其中，RingBuffer的publish(sequence)方法会调用Sequencer接口的publish()方法来设置当前生产者的Sequence序号。
abstract class RingBufferPad {
protected long p1, p2, p3, p4, p5, p6, p7;
}
abstract class RingBufferFields<E> extends RingBufferPad {
...
private static final Unsafe UNSAFE = Util.getUnsafe();
private final long indexMask;
//环形数组存储事件消息
private final Object[] entries;
protected final int bufferSize;
//RingBuffer的sequencer属性代表了当前线程对应的生产者
protected final Sequencer sequencer;
RingBufferFields(EventFactory<E> eventFactory, Sequencer sequencer) {
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.indexMask = bufferSize - 1;
//初始化数组
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//内存预加载
fill(eventFactory);
}
private void fill(EventFactory<E> eventFactory) {
for (int i = 0; i < bufferSize; i++) {
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
protected final E elementAt(long sequence) {
return (E) UNSAFE.getObject(entries, REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT));
}
...
}
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
protected long p1, p2, p3, p4, p5, p6, p7;
...
//Increment and return the next sequence for the ring buffer.
//Calls of this method should ensure that they always publish the sequence afterward.
//E.g.
//long sequence = ringBuffer.next();
//try {
// Event e = ringBuffer.get(sequence);
// //Do some work with the event.
//} finally {
// ringBuffer.publish(sequence);
//}
//@return The next sequence to publish to.
//@see RingBuffer#publish(long)
//@see RingBuffer#get(long)
@Override
public long next() {
return sequencer.next();
}
//Publish the specified sequence.
//This action marks this particular message as being available to be read.
//@param sequence the sequence to publish.
@Override
public void publish(long sequence) {
sequencer.publish(sequence);
}
//Get the event for a given sequence in the RingBuffer.
//This call has 2 uses.
//Firstly use this call when publishing to a ring buffer.
//After calling RingBuffer#next() use this call to get hold of the preallocated event to fill with data before calling RingBuffer#publish(long).
//Secondly use this call when consuming data from the ring buffer.
//After calling SequenceBarrier#waitFor(long) call this method with any value greater than that
//your current consumer sequence and less than or equal to the value returned from the SequenceBarrier#waitFor(long) method.
//@param sequence for the event
//@return the event for the given sequence
@Override
public E get(long sequence) {
//调用父类RingBufferFields的elementAt()方法
return elementAt(sequence);
}
...
}
RingBuffer的sequencer属性会在创建RingBuffer对象时传入，而创建RingBuffer对象的时机则是在初始化Disruptor的时候。
在Disruptor的构造方法中，会调用RingBuffer的create()方法，RingBuffer的create()方法会根据不同的生产者类型来初始化sequencer属性。
由生产者线程通过new创建的Sequencer接口实现类的实例就是一个生产者。单生产者的线程执行上面的main()方法时，会创建一个单生产者Sequencer实例来代表生产者。多生产者的线程执行如下的main()方法时，会创建一个多生产者Sequencer实例来代表生产者。
public class Disruptor<T> {
private final RingBuffer<T> ringBuffer;
private final Executor executor;
private final ConsumerRepository<T> consumerRepository = new ConsumerRepository<T>();
private final AtomicBoolean started = new AtomicBoolean(false);
private ExceptionHandler<? super T> exceptionHandler;
...
//Create a new Disruptor.
//@param eventFactory the factory to create events in the ring buffer.
//@param ringBufferSize the size of the ring buffer, must be power of 2.
//@param executor an Executor to execute event processors.
//@param producerType the claim strategy to use for the ring buffer.
//@param waitStrategy the wait strategy to use for the ring buffer.
public Disruptor(final EventFactory<T> eventFactory, final int ringBufferSize, final Executor executor, final ProducerType producerType, final WaitStrategy waitStrategy) {
this(RingBuffer.create(producerType, eventFactory, ringBufferSize, waitStrategy), executor);
}
private Disruptor(final RingBuffer<T> ringBuffer, final Executor executor) {
this.ringBuffer = ringBuffer;
this.executor = executor;
}
...
}
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
protected long p1, p2, p3, p4, p5, p6, p7;
...
//Create a new Ring Buffer with the specified producer type (SINGLE or MULTI)
//@param producerType producer type to use ProducerType.
//@param factory used to create events within the ring buffer.
//@param bufferSize number of elements to create within the ring buffer.
//@param waitStrategy used to determine how to wait for new elements to become available.
public static <E> RingBuffer<E> create(ProducerType producerType, EventFactory<E> factory, int bufferSize, WaitStrategy waitStrategy) {
switch (producerType) {
case SINGLE:
//单生产者模式下的当前生产者是一个SingleProducerSequencer实例
return createSingleProducer(factory, bufferSize, waitStrategy);
case MULTI:
//多生产者模式下的当前生产者是一个MultiProducerSequencer实例
return createMultiProducer(factory, bufferSize, waitStrategy);
default:
throw new IllegalStateException(producerType.toString());
}
}
//Create a new single producer RingBuffer with the specified wait strategy.
//@param <E> Class of the event stored in the ring buffer.
//@param factory used to create the events within the ring buffer.
//@param bufferSize number of elements to create within the ring buffer.
//@param waitStrategy used to determine how to wait for new elements to become available.
//@return a constructed ring buffer.
public static <E> RingBuffer<E> createSingleProducer(EventFactory<E> factory, int bufferSize, WaitStrategy waitStrategy) {
SingleProducerSequencer sequencer = new SingleProducerSequencer(bufferSize, waitStrategy);
return new RingBuffer<E>(factory, sequencer);
}
//Create a new multiple producer RingBuffer with the specified wait strategy.
//@param <E> Class of the event stored in the ring buffer.
//@param factory used to create the events within the ring buffer.
//@param bufferSize number of elements to create within the ring buffer.
//@param waitStrategy used to determine how to wait for new elements to become available.
//@return a constructed ring buffer.
public static <E> RingBuffer<E> createMultiProducer(EventFactory<E> factory, int bufferSize, WaitStrategy waitStrategy) {
MultiProducerSequencer sequencer = new MultiProducerSequencer(bufferSize, waitStrategy);
return new RingBuffer<E>(factory, sequencer);
}
//Construct a RingBuffer with the full option set.
//@param eventFactory to newInstance entries for filling the RingBuffer
//@param sequencer sequencer to handle the ordering of events moving through the RingBuffer.
RingBuffer(EventFactory<E> eventFactory, Sequencer sequencer) {
super(eventFactory, sequencer);
}
...
}
abstract class RingBufferPad {
protected long p1, p2, p3, p4, p5, p6, p7;
}
abstract class RingBufferFields<E> extends RingBufferPad {
...
private final long indexMask;
//环形数组存储事件消息
private final Object[] entries;
protected final int bufferSize;
//RingBuffer的sequencer属性代表了当前线程对应的生产者
protected final Sequencer sequencer;
RingBufferFields(EventFactory<E> eventFactory, Sequencer sequencer) {
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.indexMask = bufferSize - 1;
//初始化数组
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//内存预加载
fill(eventFactory);
}
private void fill(EventFactory<E> eventFactory) {
for (int i = 0; i < bufferSize; i++) {
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
...
}
SingleProducerSequencer的publish()方法在发布事件消息时，首先会设置当前生产者的Sequence，然后会通过等待策略通知阻塞的消费者。
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
...
//Publish the specified sequence.
//This action marks this particular message as being available to be read.
//@param sequence the sequence to publish.
@Override
public void publish(long sequence) {
sequencer.publish(sequence);
}
...
}
public abstract class AbstractSequencer implements Sequencer {
private static final AtomicReferenceFieldUpdater<AbstractSequencer, Sequence[]> SEQUENCE_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(AbstractSequencer.class, Sequence[].class, "gatingSequences");
//环形数组的大小
protected final int bufferSize;
//等待策略
protected final WaitStrategy waitStrategy;
//当前生产者的进度
protected final Sequence cursor = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
//每一个Sequence都对应着一个消费者(一个EventHandler或者一个WorkHandler)
//这些Sequence会通过SEQUENCE_UPDATER在执行Disruptor的handleEventsWith()等方法时，
//由RingBuffer的addGatingSequences()方法进行添加
protected volatile Sequence[] gatingSequences = new Sequence[0];
...
//Create with the specified buffer size and wait strategy.
//@param bufferSize The total number of entries, must be a positive power of 2.
//@param waitStrategy
public AbstractSequencer(int bufferSize, WaitStrategy waitStrategy) {
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.bufferSize = bufferSize;
this.waitStrategy = waitStrategy;
}
...
}
abstract class SingleProducerSequencerPad extends AbstractSequencer {
protected long p1, p2, p3, p4, p5, p6, p7;
public SingleProducerSequencerPad(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
}
abstract class SingleProducerSequencerFields extends SingleProducerSequencerPad {
public SingleProducerSequencerFields(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
//表示生产者的当前序号，值为-1
protected long nextValue = Sequence.INITIAL_VALUE;
//表示消费者的最小序号，值为-1
protected long cachedValue = Sequence.INITIAL_VALUE;
}
public final class SingleProducerSequencer extends SingleProducerSequencerFields {
protected long p1, p2, p3, p4, p5, p6, p7;
//Construct a Sequencer with the selected wait strategy and buffer size.
//@param bufferSize the size of the buffer that this will sequence over.
//@param waitStrategy for those waiting on sequences.
public SingleProducerSequencer(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
@Override
public void publish(long sequence) {
//设置当前生产者的进度，cursor代表了当前生产者的Sequence
cursor.set(sequence);
//通过等待策略通知阻塞的消费者
waitStrategy.signalAllWhenBlocking();
}
@Override
public long next() {
return next(1);
}
@Override
public long next(int n) {
if (n < 1) {
throw new IllegalArgumentException("n must be > 0");
}
long nextValue = this.nextValue;
long nextSequence = nextValue + n;
long wrapPoint = nextSequence - bufferSize;
long cachedGatingSequence = this.cachedValue;
if (wrapPoint > cachedGatingSequence || cachedGatingSequence > nextValue) {
long minSequence;
while (wrapPoint > (minSequence = Util.getMinimumSequence(gatingSequences, nextValue))) {
LockSupport.parkNanos(1L);
}
this.cachedValue = minSequence;
}
this.nextValue = nextSequence;
return nextSequence;
}
...
}
class LhsPadding {
protected long p1, p2, p3, p4, p5, p6, p7;
}
class Value extends LhsPadding {
protected volatile long value;
}
class RhsPadding extends Value {
protected long p9, p10, p11, p12, p13, p14, p15;
}
//Concurrent sequence class used for tracking the progress of the ring buffer and event processors.
//Support a number of concurrent operations including CAS and order writes.
//Also attempts to be more efficient with regards to false sharing by adding padding around the volatile field.
public class Sequence extends RhsPadding {
static final long INITIAL_VALUE = -1L;
private static final Unsafe UNSAFE;
private static final long VALUE_OFFSET;
static {
UNSAFE = Util.getUnsafe();
VALUE_OFFSET = UNSAFE.objectFieldOffset(Value.class.getDeclaredField("value"));
}
//Create a sequence initialised to -1.
public Sequence() {
this(INITIAL_VALUE);
}
//Create a sequence with a specified initial value.
//@param initialValue The initial value for this sequence.
public Sequence(final long initialValue) {
UNSAFE.putOrderedLong(this, VALUE_OFFSET, initialValue);
}
//Perform a volatile read of this sequence's value.
//@return The current value of the sequence.
public long get() {
return value;
}
//Perform an ordered write of this sequence.
//The intent is a Store/Store barrier between this write and any previous store.
//@param value The new value for the sequence.
public void set(final long value) {
UNSAFE.putOrderedLong(this, VALUE_OFFSET, value);
}
//Performs a volatile write of this sequence.
//The intent is a Store/Store barrier between this write and
//any previous write and a Store/Load barrier between this write and
//any subsequent volatile read.
//@param value The new value for the sequence.
public void setVolatile(final long value) {
UNSAFE.putLongVolatile(this, VALUE_OFFSET, value);
}
//Perform a compare and set operation on the sequence.
//@param expectedValue The expected current value.
//@param newValue The value to update to.
//@return true if the operation succeeds, false otherwise.
public boolean compareAndSet(final long expectedValue, final long newValue) {
return UNSAFE.compareAndSwapLong(this, VALUE_OFFSET, expectedValue, newValue);
}
//Atomically increment the sequence by one.
//@return The value after the increment
public long incrementAndGet() {
return addAndGet(1L);
}
//Atomically add the supplied value.
//@param increment The value to add to the sequence.
//@return The value after the increment.
public long addAndGet(final long increment) {
long currentValue;
long newValue;
do {
currentValue = get();
newValue = currentValue + increment;
} while (!compareAndSet(currentValue, newValue));
return newValue;
}
@Override
public String toString() {
return Long.toString(get());
}
}
MultiProducerSequencer的publish()方法在发布事件消息时，则会通过UnSafe设置sequence在int数组中对应元素的值。
public final class MultiProducerSequencer extends AbstractSequencer {
private static final Unsafe UNSAFE = Util.getUnsafe();
private static final long BASE = UNSAFE.arrayBaseOffset(int[].class);
private static final long SCALE = UNSAFE.arrayIndexScale(int[].class);
private final int[] availableBuffer;
private final int indexMask;
private final int indexShift;
//Construct a Sequencer with the selected wait strategy and buffer size.
//@param bufferSize the size of the buffer that this will sequence over.
//@param waitStrategy for those waiting on sequences.
public MultiProducerSequencer(int bufferSize, final WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
availableBuffer = new int[bufferSize];
indexMask = bufferSize - 1;
indexShift = Util.log2(bufferSize);
initialiseAvailableBuffer();
}
private void initialiseAvailableBuffer() {
for (int i = availableBuffer.length - 1; i != 0; i--) {
setAvailableBufferValue(i, -1);
}
setAvailableBufferValue(0, -1);
}
private void setAvailableBufferValue(int index, int flag) {
long bufferAddress = (index * SCALE) + BASE;
UNSAFE.putOrderedInt(availableBuffer, bufferAddress, flag);
}
@Override
public void publish(final long sequence) {
setAvailable(sequence);
waitStrategy.signalAllWhenBlocking();
}
//The below methods work on the availableBuffer flag.
//The prime reason is to avoid a shared sequence object between publisher threads.
//(Keeping single pointers tracking start and end would require coordination between the threads).
//-- Firstly we have the constraint that the delta between the cursor and minimum gating sequence
//will never be larger than the buffer size (the code in next/tryNext in the Sequence takes care of that).
//-- Given that; take the sequence value and mask off the lower portion of the sequence
//as the index into the buffer (indexMask). (aka modulo operator)
//-- The upper portion of the sequence becomes the value to check for availability.
//ie: it tells us how many times around the ring buffer we've been (aka division)
//-- Because we can't wrap without the gating sequences moving forward
//(i.e. the minimum gating sequence is effectively our last available position in the buffer),
//when we have new data and successfully claimed a slot we can simply write over the top.
private void setAvailable(final long sequence) {
setAvailableBufferValue(calculateIndex(sequence), calculateAvailabilityFlag(sequence));
}
private int calculateIndex(final long sequence) {
return ((int) sequence) & indexMask;
}
private int calculateAvailabilityFlag(final long sequence) {
return (int) (sequence >>> indexShift);
}
@Override
public long next() {
return next(1);
}
@Override
public long next(int n) {
if (n < 1) {
throw new IllegalArgumentException("n must be > 0");
}
long current;
long next;
do {
current = cursor.get();
next = current + n;
long wrapPoint = next - bufferSize;
long cachedGatingSequence = gatingSequenceCache.get();
if (wrapPoint > cachedGatingSequence || cachedGatingSequence > current) {
long gatingSequence = Util.getMinimumSequence(gatingSequences, current);
if (wrapPoint > gatingSequence) {
LockSupport.parkNanos(1);
continue;
}
gatingSequenceCache.set(gatingSequence);
} else if (cursor.compareAndSet(current, next)) {
break;
}
} while (true);
return next;
}
...
}
(2)通过Translator事件转换器发布消息
生产者还可以直接调用RingBuffer的tryPublishEvent()方法来完成发布事件消息到RingBuffer。该方法首先会调用Sequencer接口的tryNext()方法获取sequence序号，然后根据该sequence序号从RingBuffer的环形数组中获取对应的元素，接着再调用RingBuffer的translateAndPublish()方法将事件消息赋值替换到该元素中，最后调用Sequencer接口的publish()方法设置当前生产者的sequence序号来完成事件消息的发布。
abstract class RingBufferPad {
protected long p1, p2, p3, p4, p5, p6, p7;
}
abstract class RingBufferFields<E> extends RingBufferPad {
...
private static final Unsafe UNSAFE = Util.getUnsafe();
private final long indexMask;
//环形数组存储事件消息
private final Object[] entries;
protected final int bufferSize;
//RingBuffer的sequencer属性代表了当前线程对应的生产者
protected final Sequencer sequencer;
RingBufferFields(EventFactory<E> eventFactory, Sequencer sequencer) {
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.indexMask = bufferSize - 1;
//初始化数组
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//内存预加载
fill(eventFactory);
}
private void fill(EventFactory<E> eventFactory) {
for (int i = 0; i < bufferSize; i++) {
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
protected final E elementAt(long sequence) {
return (E) UNSAFE.getObject(entries, REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT));
}
...
}
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
//值为-1
public static final long INITIAL_CURSOR_VALUE = Sequence.INITIAL_VALUE;
protected long p1, p2, p3, p4, p5, p6, p7;
//Construct a RingBuffer with the full option set.
//@param eventFactory to newInstance entries for filling the RingBuffer
//@param sequencer sequencer to handle the ordering of events moving through the RingBuffer.
RingBuffer(EventFactory<E> eventFactory, Sequencer sequencer) {
super(eventFactory, sequencer);
}
@Override
public boolean tryPublishEvent(EventTranslator<E> translator) {
try {
final long sequence = sequencer.tryNext();
translateAndPublish(translator, sequence);
return true;
} catch (InsufficientCapacityException e) {
return false;
}
}
private void translateAndPublish(EventTranslator<E> translator, long sequence) {
try {
translator.translateTo(get(sequence), sequence);
} finally {
sequencer.publish(sequence);
}
}
//Get the event for a given sequence in the RingBuffer.
//This call has 2 uses.
//Firstly use this call when publishing to a ring buffer.
//After calling RingBuffer#next() use this call to get hold of the preallocated event to fill with data before calling RingBuffer#publish(long).
//Secondly use this call when consuming data from the ring buffer.
//After calling SequenceBarrier#waitFor(long) call this method with any value greater than that
//your current consumer sequence and less than or equal to the value returned from the SequenceBarrier#waitFor(long) method.
//@param sequence for the event
//@return the event for the given sequence
@Override
public E get(long sequence) {
//调用父类RingBufferFields的elementAt()方法
return elementAt(sequence);
}
...
}
public abstract class AbstractSequencer implements Sequencer {
private static final AtomicReferenceFieldUpdater<AbstractSequencer, Sequence[]> SEQUENCE_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(AbstractSequencer.class, Sequence[].class, "gatingSequences");
//环形数组的大小
protected final int bufferSize;
//等待策略
protected final WaitStrategy waitStrategy;
//当前生产者的进度
protected final Sequence cursor = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
//每一个Sequence都对应着一个消费者(一个EventHandler或者一个WorkHandler)
//这些Sequence会通过SEQUENCE_UPDATER在执行Disruptor的handleEventsWith()等方法时，
//由RingBuffer的addGatingSequences()方法进行添加
protected volatile Sequence[] gatingSequences = new Sequence[0];
...
//Create with the specified buffer size and wait strategy.
//@param bufferSize The total number of entries, must be a positive power of 2.
//@param waitStrategy
public AbstractSequencer(int bufferSize, WaitStrategy waitStrategy) {
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.bufferSize = bufferSize;
this.waitStrategy = waitStrategy;
}
...
}
public final class SingleProducerSequencer extends SingleProducerSequencerFields {
protected long p1, p2, p3, p4, p5, p6, p7;
//Construct a Sequencer with the selected wait strategy and buffer size.
//@param bufferSize the size of the buffer that this will sequence over.
//@param waitStrategy for those waiting on sequences.
public SingleProducerSequencer(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
...
@Override
public long tryNext() throws InsufficientCapacityException {
return tryNext(1);
}
@Override
public long tryNext(int n) throws InsufficientCapacityException {
if (n < 1) {
throw new IllegalArgumentException("n must be > 0");
}
if (!hasAvailableCapacity(n, true)) {
throw InsufficientCapacityException.INSTANCE;
}
long nextSequence = this.nextValue += n;
return nextSequence;
}
private boolean hasAvailableCapacity(int requiredCapacity, boolean doStore) {
long nextValue = this.nextValue;
long wrapPoint = (nextValue + requiredCapacity) - bufferSize;
long cachedGatingSequence = this.cachedValue;
if (wrapPoint > cachedGatingSequence || cachedGatingSequence > nextValue) {
if (doStore) {
cursor.setVolatile(nextValue);//StoreLoad fence
}
long minSequence = Util.getMinimumSequence(gatingSequences, nextValue);
this.cachedValue = minSequence;
if (wrapPoint > minSequence) {
return false;
}
}
return true;
}
@Override
public void publish(long sequence) {
//设置当前生产者的sequence
cursor.set(sequence);
//通过等待策略通知阻塞的消费者
waitStrategy.signalAllWhenBlocking();
}
...
}
abstract class SingleProducerSequencerFields extends SingleProducerSequencerPad {
SingleProducerSequencerFields(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
//表示生产者的当前序号，值为-1
protected long nextValue = Sequence.INITIAL_VALUE;
//表示消费者的最小序号，值为-1
protected long cachedValue = Sequence.INITIAL_VALUE;
}
abstract class SingleProducerSequencerPad extends AbstractSequencer {
protected long p1, p2, p3, p4, p5, p6, p7;
SingleProducerSequencerPad(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
}
public final class MultiProducerSequencer extends AbstractSequencer {
...
@Override
public long tryNext() throws InsufficientCapacityException {
return tryNext(1);
}
@Override
public long tryNext(int n) throws InsufficientCapacityException {
if (n < 1) {
throw new IllegalArgumentException("n must be > 0");
}
long current;
long next;
do {
current = cursor.get();
next = current + n;
if (!hasAvailableCapacity(gatingSequences, n, current)) {
throw InsufficientCapacityException.INSTANCE;
}
} while (!cursor.compareAndSet(current, next));
return next;
}
private boolean hasAvailableCapacity(Sequence[] gatingSequences, final int requiredCapacity, long cursorValue) {
long wrapPoint = (cursorValue + requiredCapacity) - bufferSize;
long cachedGatingSequence = gatingSequenceCache.get();
if (wrapPoint > cachedGatingSequence || cachedGatingSequence > cursorValue) {
long minSequence = Util.getMinimumSequence(gatingSequences, cursorValue);
gatingSequenceCache.set(minSequence);
if (wrapPoint > minSequence) {
return false;
}
}
return true;
}
@Override
public void publish(final long sequence) {
setAvailable(sequence);
waitStrategy.signalAllWhenBlocking();
}
...
}
//Implementations translate (write) data representations into events claimed from the RingBuffer.
//When publishing to the RingBuffer, provide an EventTranslator.
//The RingBuffer will select the next available event by sequence and provide it to the EventTranslator (which should update the event),
//before publishing the sequence update.
//@param <T> event implementation storing the data for sharing during exchange or parallel coordination of an event.
public interface EventTranslator<T> {
//Translate a data representation into fields set in given event
//@param event into which the data should be translated.
//@param sequence that is assigned to event.
void translateTo(T event, long sequence);
}
2.Disruptor的消费者源码分析
Disruptor的消费者主要由BatchEventProcessor类和WorkProcessor类来实现，并通过Disruptor的handleEventsWith()方法或者handleEventsWithWorkerPool()方法和start()方法来启动。
执行Disruptor的handleEventsWith()方法绑定消费者时，会创建BatchEventProcessor对象，并将其添加到Disruptor的consumerRepository属性。
执行Disruptor的handleEventsWithWorkerPool()方法绑定消费者时，则会创建WorkProcessor对象，并将该对象添加到Disruptor的consumerRepository属性。
执行Disruptor的start()方法启动Disruptor实例时，便会通过线程池执行BatchEventProcessor里的run()方法，或者通过线程池执行WorkProcessor里的run()方法。
执行BatchEventProcessor的run()方法时，会通过修改BatchEventProcessor的sequence来实现消费RingBuffer的数据。
执行WorkProcessor的run()方法时，会通过修改WorkProcessor的sequence来实现消费RingBuffer的数据。
public class Main {
public static void main(String[] args) {
//参数准备
OrderEventFactory orderEventFactory = new OrderEventFactory();
int ringBufferSize = 4;
ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
//参数一：eventFactory，消息(Event)工厂对象
//参数二：ringBufferSize，容器的长度
//参数三：executor，线程池(建议使用自定义线程池)，RejectedExecutionHandler
//参数四：ProducerType，单生产者还是多生产者
//参数五：waitStrategy，等待策略
//1.实例化Disruptor对象
Disruptor<OrderEvent> disruptor = new Disruptor<OrderEvent>(
orderEventFactory,
ringBufferSize,
executor,
ProducerType.SINGLE,
new BlockingWaitStrategy()
);
//2.添加Event处理器，用于处理事件
//也就是构建Disruptor与消费者的一个关联关系
//方式一：使用handleEventsWith()方法
disruptor.handleEventsWith(new OrderEventHandler());
//方式二：使用handleEventsWithWorkerPool()方法
//disruptor.handleEventsWithWorkerPool(workHandlers);
//3.启动disruptor
disruptor.start();
//4.获取实际存储数据的容器: RingBuffer
RingBuffer<OrderEvent> ringBuffer = disruptor.getRingBuffer();
OrderEventProducer producer = new OrderEventProducer(ringBuffer);
ByteBuffer bb = ByteBuffer.allocate(8);
for (long i = 0; i < 5; i++) {
bb.putLong(0, i);
//向容器中投递数据
producer.sendData(bb);
}
disruptor.shutdown();
executor.shutdown();
}
}
public class Disruptor<T> {
private final RingBuffer<T> ringBuffer;
private final Executor executor;
private final ConsumerRepository<T> consumerRepository = new ConsumerRepository<T>();
private final AtomicBoolean started = new AtomicBoolean(false);
private ExceptionHandler<? super T> exceptionHandler;
...
//绑定消费者，设置EventHandler，创建EventProcessor
//Set up event handlers to handle events from the ring buffer.
//These handlers will process events as soon as they become available, in parallel.
//This method can be used as the start of a chain.
//For example if the handler A must process events before handler B: dw.handleEventsWith(A).then(B);
//@param handlers the event handlers that will process events.
//@return a EventHandlerGroup that can be used to chain dependencies.
@SuppressWarnings("varargs")
public EventHandlerGroup<T> handleEventsWith(final EventHandler<? super T>... handlers) {
return createEventProcessors(new Sequence[0], handlers);
}
//创建BatchEventProcessor，添加到consumerRepository中
EventHandlerGroup<T> createEventProcessors(final Sequence[] barrierSequences, final EventHandler<? super T>[] eventHandlers) {
checkNotStarted();
final Sequence[] processorSequences = new Sequence[eventHandlers.length];
final SequenceBarrier barrier = ringBuffer.newBarrier(barrierSequences);
for (int i = 0, eventHandlersLength = eventHandlers.length; i < eventHandlersLength; i++) {
final EventHandler<? super T> eventHandler = eventHandlers[i];
//创建BatchEventProcessor对象
final BatchEventProcessor<T> batchEventProcessor =
new BatchEventProcessor<>(ringBuffer, barrier, eventHandler);
if (exceptionHandler != null) {
batchEventProcessor.setExceptionHandler(exceptionHandler);
}
//添加BatchEventProcessor对象到consumerRepository中
consumerRepository.add(batchEventProcessor, eventHandler, barrier);
//一个消费者线程对应一个batchEventProcessor
//每个batchEventProcessor都会持有一个Sequence对象来表示当前消费者线程的消费进度
processorSequences[i] = batchEventProcessor.getSequence();
}
//将每个消费者线程持有的Sequence对象添加到生产者Sequencer的gatingSequences属性中(Sequence[]属性)
updateGatingSequencesForNextInChain(barrierSequences, processorSequences);
return new EventHandlerGroup<>(this, consumerRepository, processorSequences);
}
private void updateGatingSequencesForNextInChain(final Sequence[] barrierSequences, final Sequence[] processorSequences) {
if (processorSequences.length > 0) {
ringBuffer.addGatingSequences(processorSequences);
for (final Sequence barrierSequence : barrierSequences) {
ringBuffer.removeGatingSequence(barrierSequence);
}
consumerRepository.unMarkEventProcessorsAsEndOfChain(barrierSequences);
}
}
private void checkNotStarted() {
//线程的开关会使用CAS实现
if (started.get()) {
throw new IllegalStateException("All event handlers must be added before calling starts.");
}
}
...
//Starts the event processors and returns the fully configured ring buffer.
//The ring buffer is set up to prevent overwriting any entry that is yet to be processed by the slowest event processor.
//This method must only be called once after all event processors have been added.
//@return the configured ring buffer.
public RingBuffer<T> start() {
checkOnlyStartedOnce();
for (final ConsumerInfo consumerInfo : consumerRepository) {
//在执行Disruptor.handleEventsWith()方法，调用Disruptor.createEventProcessors()方法时，
//会将新创建的BatchEventProcessor对象封装成EventProcessorInfo对象(即ConsumerInfo对象)，
//然后通过add()方法添加到consumerRepository中
//所以下面会调用EventProcessorInfo.start()方法
consumerInfo.start(executor);
}
return ringBuffer;
}
private void checkOnlyStartedOnce() {
//线程的开关使用CAS实现
if (!started.compareAndSet(false, true)) {
throw new IllegalStateException("Disruptor.start() must only be called once.");
}
}
...
}
//Provides a repository mechanism to associate EventHandlers with EventProcessors
class ConsumerRepository<T> implements Iterable<ConsumerInfo> {
private final Map<EventHandler<?>, EventProcessorInfo<T>> eventProcessorInfoByEventHandler = new IdentityHashMap<EventHandler<?>, EventProcessorInfo<T>>();
private final Map<Sequence, ConsumerInfo> eventProcessorInfoBySequence = new IdentityHashMap<Sequence, ConsumerInfo>();
private final Collection<ConsumerInfo> consumerInfos = new ArrayList<ConsumerInfo>();
//添加BatchEventProcessor对象到consumerRepository中
public void add(final EventProcessor eventprocessor, final EventHandler<? super T> handler, final SequenceBarrier barrier) {
//将传入的BatchEventProcessor对象封装成EventProcessorInfo对象，即ConsumerInfo对象
final EventProcessorInfo<T> consumerInfo = new EventProcessorInfo<T>(eventprocessor, handler, barrier);
eventProcessorInfoByEventHandler.put(handler, consumerInfo);
eventProcessorInfoBySequence.put(eventprocessor.getSequence(), consumerInfo);
consumerInfos.add(consumerInfo);
}
...
}
class EventProcessorInfo<T> implements ConsumerInfo {
private final EventProcessor eventprocessor;
private final EventHandler<? super T> handler;
private final SequenceBarrier barrier;
private boolean endOfChain = true;
EventProcessorInfo(final EventProcessor eventprocessor, final EventHandler<? super T> handler, final SequenceBarrier barrier) {
this.eventprocessor = eventprocessor;
this.handler = handler;
this.barrier = barrier;
}
...
@Override
public void start(final Executor executor) {
//通过传入的线程池，执行BatchEventProcessor对象的run()方法
//传入的线程池，其实就是初始化Disruptor时指定的线程池
executor.execute(eventprocessor);
}
...
}
//Convenience class for handling the batching semantics of consuming entries from
//a RingBuffer and delegating the available events to an EventHandler.
//If the EventHandler also implements LifecycleAware it will be notified just after
//the thread is started and just before the thread is shutdown.
//@param <T> event implementation storing the data for sharing during exchange or parallel coordination of an event.
public final class BatchEventProcessor<T> implements EventProcessor {
private final AtomicBoolean running = new AtomicBoolean(false);
private ExceptionHandler<? super T> exceptionHandler = new FatalExceptionHandler();
private final DataProvider<T> dataProvider;
private final SequenceBarrier sequenceBarrier;
private final EventHandler<? super T> eventHandler;
private final Sequence sequence = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
private final TimeoutHandler timeoutHandler;
//Construct a EventProcessor that will automatically track the progress by
//updating its sequence when the EventHandler#onEvent(Object, long, boolean) method returns.
//@param dataProvider to which events are published.
//@param sequenceBarrier on which it is waiting.
//@param eventHandler is the delegate to which events are dispatched.
public BatchEventProcessor(final DataProvider<T> dataProvider, final SequenceBarrier sequenceBarrier, final EventHandler<? super T> eventHandler) {
//传入的dataProvider其实就是Disruptor的ringBuffer
this.dataProvider = dataProvider;
this.sequenceBarrier = sequenceBarrier;
this.eventHandler = eventHandler;
if (eventHandler instanceof SequenceReportingEventHandler) {
((SequenceReportingEventHandler<?>)eventHandler).setSequenceCallback(sequence);
}
timeoutHandler = (eventHandler instanceof TimeoutHandler) ? (TimeoutHandler) eventHandler : null;
}
...
//It is ok to have another thread rerun this method after a halt().
//通过对sequence进行修改来实现消费RingBuffer里的数据
@Override
public void run() {
if (running.compareAndSet(IDLE, RUNNING)) {
sequenceBarrier.clearAlert();
notifyStart();
try {
if (running.get() == RUNNING) {
processEvents();
}
} finally {
notifyShutdown();
running.set(IDLE);
}
} else {
//This is a little bit of guess work.
//The running state could of changed to HALTED by this point.
//However, Java does not have compareAndExchange which is the only way to get it exactly correct.
if (running.get() == RUNNING) {
throw new IllegalStateException("Thread is already running");
} else {
earlyExit();
}
}
}
private void processEvents() {
T event = null;
long nextSequence = sequence.get() + 1L;
while (true) {
try {
//通过sequenceBarrier.waitFor()方法看看消费者是否需要等待生产者投递消息
final long availableSequence = sequenceBarrier.waitFor(nextSequence);
if (batchStartAware != null) {
batchStartAware.onBatchStart(availableSequence - nextSequence + 1);
}
while (nextSequence <= availableSequence) {
//从RingBuffer中获取要消费的数据
event = dataProvider.get(nextSequence);
//执行消费者实现的onEvent()方法来消费数据
eventHandler.onEvent(event, nextSequence, nextSequence == availableSequence);
nextSequence++;
}
//设置消费者当前的消费进度
sequence.set(availableSequence);
} catch (final TimeoutException e) {
notifyTimeout(sequence.get());
} catch (final AlertException ex) {
if (running.get() != RUNNING) {
break;
}
} catch (final Throwable ex) {
handleEventException(ex, nextSequence, event);
sequence.set(nextSequence);
nextSequence++;
}
}
}
private void earlyExit() {
notifyStart();
notifyShutdown();
}
private void notifyTimeout(final long availableSequence) {
try {
if (timeoutHandler != null) {
timeoutHandler.onTimeout(availableSequence);
}
} catch (Throwable e) {
handleEventException(e, availableSequence, null);
}
}
//Notifies the EventHandler when this processor is starting up
private void notifyStart() {
if (eventHandler instanceof LifecycleAware) {
try {
((LifecycleAware) eventHandler).onStart();
} catch (final Throwable ex) {
handleOnStartException(ex);
}
}
}
//Notifies the EventHandler immediately prior to this processor shutting down
private void notifyShutdown() {
if (eventHandler instanceof LifecycleAware) {
try {
((LifecycleAware) eventHandler).onShutdown();
} catch (final Throwable ex) {
handleOnShutdownException(ex);
}
}
}
...
}
public class Disruptor<T> {
private final RingBuffer<T> ringBuffer;
private final Executor executor;
private final ConsumerRepository<T> consumerRepository = new ConsumerRepository<T>();
private final AtomicBoolean started = new AtomicBoolean(false);
private ExceptionHandler<? super T> exceptionHandler;
...
//设置WorkHandler，创建WorkProcessor
//Set up a WorkerPool to distribute an event to one of a pool of work handler threads.
//Each event will only be processed by one of the work handlers.
//The Disruptor will automatically start this processors when #start() is called.
//@param workHandlers the work handlers that will process events.
//@return a {@link EventHandlerGroup} that can be used to chain dependencies.
@SafeVarargs
@SuppressWarnings("varargs")
public final EventHandlerGroup<T> handleEventsWithWorkerPool(final WorkHandler<T>... workHandlers) {
return createWorkerPool(new Sequence[0], workHandlers);
}
//创建WorkerPool，添加到consumerRepository中
EventHandlerGroup<T> createWorkerPool(final Sequence[] barrierSequences, final WorkHandler<? super T>[] workHandlers) {
final SequenceBarrier sequenceBarrier = ringBuffer.newBarrier(barrierSequences);
//创建WorkerPool对象，以及根据workHandlers创建WorkProcessor
final WorkerPool<T> workerPool = new WorkerPool<>(ringBuffer, sequenceBarrier, exceptionHandler, workHandlers);
//添加WorkerPool对象到consumerRepository中
consumerRepository.add(workerPool, sequenceBarrier);
final Sequence[] workerSequences = workerPool.getWorkerSequences();
//将每个消费者线程持有的Sequence对象添加到生产者Sequencer的gatingSequences属性中(Sequence[]属性)
updateGatingSequencesForNextInChain(barrierSequences, workerSequences);
return new EventHandlerGroup<>(this, consumerRepository, workerSequences);
}
private void updateGatingSequencesForNextInChain(final Sequence[] barrierSequences, final Sequence[] processorSequences) {
if (processorSequences.length > 0) {
ringBuffer.addGatingSequences(processorSequences);
for (final Sequence barrierSequence : barrierSequences) {
ringBuffer.removeGatingSequence(barrierSequence);
}
consumerRepository.unMarkEventProcessorsAsEndOfChain(barrierSequences);
}
}
...
//Starts the event processors and returns the fully configured ring buffer.
//The ring buffer is set up to prevent overwriting any entry that is yet to be processed by the slowest event processor.
//This method must only be called once after all event processors have been added.
//@return the configured ring buffer.
public RingBuffer<T> start() {
checkOnlyStartedOnce();
for (final ConsumerInfo consumerInfo : consumerRepository) {
//在执行Disruptor.handleEventsWithWorkerPool()方法，调用Disruptor.createWorkerPool()方法时，
//会将新创建的WorkerPool对象封装成WorkerPoolInfo对象(即ConsumerInfo对象)，
//然后通过add()方法添加到consumerRepository中
//所以下面会调用WorkerPoolInfo.start()方法
consumerInfo.start(executor);
}
return ringBuffer;
}
private void checkOnlyStartedOnce() {
//线程的开关使用CAS实现
if (!started.compareAndSet(false, true)) {
throw new IllegalStateException("Disruptor.start() must only be called once.");
}
}
...
}
//Provides a repository mechanism to associate EventHandlers with EventProcessors
class ConsumerRepository<T> implements Iterable<ConsumerInfo> {
private final Map<EventHandler<?>, EventProcessorInfo<T>> eventProcessorInfoByEventHandler = new IdentityHashMap<EventHandler<?>, EventProcessorInfo<T>>();
private final Map<Sequence, ConsumerInfo> eventProcessorInfoBySequence = new IdentityHashMap<Sequence, ConsumerInfo>();
private final Collection<ConsumerInfo> consumerInfos = new ArrayList<ConsumerInfo>();
//添加WorkerPool对象到consumerRepository中
public void add(final WorkerPool<T> workerPool, final SequenceBarrier sequenceBarrier) {
final WorkerPoolInfo<T> workerPoolInfo = new WorkerPoolInfo<>(workerPool, sequenceBarrier);
consumerInfos.add(workerPoolInfo);
for (Sequence sequence : workerPool.getWorkerSequences()) {
eventProcessorInfoBySequence.put(sequence, workerPoolInfo);
}
}
...
}
class WorkerPoolInfo<T> implements ConsumerInfo {
private final WorkerPool<T> workerPool;
private final SequenceBarrier sequenceBarrier;
private boolean endOfChain = true;
WorkerPoolInfo(final WorkerPool<T> workerPool, final SequenceBarrier sequenceBarrier) {
this.workerPool = workerPool;
this.sequenceBarrier = sequenceBarrier;
}
@Override
public void start(Executor executor) {
workerPool.start(executor);
}
...
}
public final class WorkerPool<T> {
private final AtomicBoolean started = new AtomicBoolean(false);
private final Sequence workSequence = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
private final RingBuffer<T> ringBuffer;
//WorkProcessors are created to wrap each of the provided WorkHandlers
private final WorkProcessor<?>[] workProcessors;
//Create a worker pool to enable an array of WorkHandlers to consume published sequences.
//This option requires a pre-configured RingBuffer which must have RingBuffer#addGatingSequences(Sequence...) called before the work pool is started.
//@param ringBuffer of events to be consumed.
//@param sequenceBarrier on which the workers will depend.
//@param exceptionHandler to callback when an error occurs which is not handled by the {@link WorkHandler}s.
//@param workHandlers to distribute the work load across.
@SafeVarargs
public WorkerPool(final RingBuffer<T> ringBuffer, final SequenceBarrier sequenceBarrier, final ExceptionHandler<? super T> exceptionHandler, final WorkHandler<? super T>... workHandlers) {
this.ringBuffer = ringBuffer;
final int numWorkers = workHandlers.length;
//根据workHandlers创建WorkProcessor
workProcessors = new WorkProcessor[numWorkers];
for (int i = 0; i < numWorkers; i++) {
workProcessors[i] = new WorkProcessor<>(ringBuffer, sequenceBarrier, workHandlers[i], exceptionHandler, workSequence);
}
}
//Start the worker pool processing events in sequence.
//@param executor providing threads for running the workers.
//@return the {@link RingBuffer} used for the work queue.
//@throws IllegalStateException if the pool has already been started and not halted yet
public RingBuffer<T> start(final Executor executor) {
if (!started.compareAndSet(false, true)) {
throw new IllegalStateException("WorkerPool has already been started and cannot be restarted until halted.");
}
final long cursor = ringBuffer.getCursor();
workSequence.set(cursor);
for (WorkProcessor<?> processor : workProcessors) {
processor.getSequence().set(cursor);
//通过传入的线程池，执行WorkProcessor对象的run()方法
executor.execute(processor);
}
return ringBuffer;
}
...
}
public final class WorkProcessor<T> implements EventProcessor {
private final AtomicBoolean running = new AtomicBoolean(false);
private final Sequence sequence = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
private final RingBuffer<T> ringBuffer;
private final SequenceBarrier sequenceBarrier;
private final WorkHandler<? super T> workHandler;
private final ExceptionHandler<? super T> exceptionHandler;
private final Sequence workSequence;
private final EventReleaser eventReleaser = new EventReleaser() {
@Override
public void release() {
sequence.set(Long.MAX_VALUE);
}
};
private final TimeoutHandler timeoutHandler;
//Construct a {@link WorkProcessor}.
//@param ringBuffer to which events are published.
//@param sequenceBarrier on which it is waiting.
//@param workHandler is the delegate to which events are dispatched.
//@param exceptionHandler to be called back when an error occurs
//@param workSequence from which to claim the next event to be worked on. It should always be initialised as Sequencer#INITIAL_CURSOR_VALUE
public WorkProcessor(final RingBuffer<T> ringBuffer, final SequenceBarrier sequenceBarrier, final WorkHandler<? super T> workHandler, final ExceptionHandler<? super T> exceptionHandler, final Sequence workSequence) {
this.ringBuffer = ringBuffer;
this.sequenceBarrier = sequenceBarrier;
this.workHandler = workHandler;
this.exceptionHandler = exceptionHandler;
this.workSequence = workSequence;
if (this.workHandler instanceof EventReleaseAware) {
((EventReleaseAware) this.workHandler).setEventReleaser(eventReleaser);
}
timeoutHandler = (workHandler instanceof TimeoutHandler) ? (TimeoutHandler) workHandler : null;
}
//通过对sequence进行修改来实现消费RingBuffer里的数据
@Override
public void run() {
if (!running.compareAndSet(false, true)) {
throw new IllegalStateException("Thread is already running");
}
sequenceBarrier.clearAlert();
notifyStart();
boolean processedSequence = true;
long cachedAvailableSequence = Long.MIN_VALUE;
long nextSequence = sequence.get();
T event = null;
while (true) {
try {
if (processedSequence) {
processedSequence = false;
do {
nextSequence = workSequence.get() + 1L;
//设置消费者当前的消费进度
sequence.set(nextSequence - 1L);
} while (!workSequence.compareAndSet(nextSequence - 1L, nextSequence));
}
if (cachedAvailableSequence >= nextSequence) {
//从RingBuffer中获取要消费的数据
event = ringBuffer.get(nextSequence);
//执行消费者实现的onEvent()方法来消费数据
workHandler.onEvent(event);
processedSequence = true;
} else {
//通过sequenceBarrier.waitFor()方法看看消费者是否需要等待生产者投递消息
cachedAvailableSequence = sequenceBarrier.waitFor(nextSequence);
}
} catch (final TimeoutException e) {
notifyTimeout(sequence.get());
} catch (final AlertException ex) {
if (!running.get()) {
break;
}
} catch (final Throwable ex) {
//handle, mark as processed, unless the exception handler threw an exception
exceptionHandler.handleEventException(ex, nextSequence, event);
processedSequence = true;
}
}
notifyShutdown();
running.set(false);
}
...
}
public class Disruptor<T> {
private final RingBuffer<T> ringBuffer;
private void updateGatingSequencesForNextInChain(final Sequence[] barrierSequences, final Sequence[] processorSequences) {
if (processorSequences.length > 0) {
ringBuffer.addGatingSequences(processorSequences);
for (final Sequence barrierSequence : barrierSequences) {
ringBuffer.removeGatingSequence(barrierSequence);
}
consumerRepository.unMarkEventProcessorsAsEndOfChain(barrierSequences);
}
}
...
}
abstract class RingBufferPad {
protected long p1, p2, p3, p4, p5, p6, p7;
}
abstract class RingBufferFields<E> extends RingBufferPad {
...
private static final Unsafe UNSAFE = Util.getUnsafe();
private final long indexMask;
//环形数组存储事件消息
private final Object[] entries;
protected final int bufferSize;
//RingBuffer的sequencer属性代表了当前线程对应的生产者
protected final Sequencer sequencer;
RingBufferFields(EventFactory<E> eventFactory, Sequencer sequencer) {
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.indexMask = bufferSize - 1;
//初始化数组
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//内存预加载
fill(eventFactory);
}
private void fill(EventFactory<E> eventFactory) {
for (int i = 0; i < bufferSize; i++) {
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
protected final E elementAt(long sequence) {
return (E) UNSAFE.getObject(entries, REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT));
}
...
}
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
...
//Add the specified gating sequences to this instance of the Disruptor.
//They will safely and atomically added to the list of gating sequences.
//@param gatingSequences The sequences to add.
public void addGatingSequences(Sequence... gatingSequences) {
sequencer.addGatingSequences(gatingSequences);
}
...
}
public interface Sequencer extends Cursored, Sequenced {
...
//Add the specified gating sequences to this instance of the Disruptor.
//They will safely and atomically added to the list of gating sequences.
//@param gatingSequences The sequences to add.
void addGatingSequences(Sequence... gatingSequences);
...
}
public abstract class AbstractSequencer implements Sequencer {
private static final AtomicReferenceFieldUpdater<AbstractSequencer, Sequence[]> SEQUENCE_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(AbstractSequencer.class, Sequence[].class, "gatingSequences");
...
@Override
public final void addGatingSequences(Sequence... gatingSequences) {
SequenceGroups.addSequences(this, SEQUENCE_UPDATER, this, gatingSequences);
}
...
}
class SequenceGroups {
static <T> void addSequences(final T holder, final AtomicReferenceFieldUpdater<T, Sequence[]> updater, final Cursored cursor, final Sequence... sequencesToAdd) {
long cursorSequence;
Sequence[] updatedSequences;
Sequence[] currentSequences;
do {
currentSequences = updater.get(holder);
updatedSequences = copyOf(currentSequences, currentSequences.length + sequencesToAdd.length);
cursorSequence = cursor.getCursor();
int index = currentSequences.length;
for (Sequence sequence : sequencesToAdd) {
sequence.set(cursorSequence);
updatedSequences[index++] = sequence;
}
} while (!updater.compareAndSet(holder, currentSequences, updatedSequences));
cursorSequence = cursor.getCursor();
for (Sequence sequence : sequencesToAdd) {
sequence.set(cursorSequence);
}
}
...
}
3.Disruptor的WaitStrategy等待策略分析
在生产者发布消息时，会调用WaitStrategy的signalAllWhenBlocking()方法唤醒阻塞的消费者。在消费者消费消息时，会调用WaitStrategy的waitFor()方法阻塞消费过快的消费者。
当然，不同的策略不一定就是阻塞消费者，比如BlockingWaitStrategy会通过ReentrantLock来阻塞消费者，而YieldingWaitStrategy则通过yield切换线程来实现让消费者无锁等待，即通过Thread的yield()方法切换线程让另一个线程继续执行自旋判断操作。
所以YieldingWaitStrategy等待策略的效率是最高的 + 最耗费CPU资源，当然效率次高、比较耗费CPU资源的是BusySpinWaitStrategy等待策略。
Disruptor提供了如下几种等待策略：
一.完全阻塞的等待策略BlockingWaitStrategy 二.切换线程自旋的等待策略YieldingWaitStrategy 三.繁忙自旋的等待策略BusySpinWaitStrategy 四.轻微阻塞的等待策略LiteBlockingWaitStrategy 也就是唤醒阻塞线程时，通过GAS避免并发获取锁的等待策略 五.最小睡眠 + 切换线程的等待策略SleepingWaitStrategy
总结：
为了达到最高效率，有大量CPU资源，可切换线程让多个线程自旋判断 为了保证高效的同时兼顾CPU资源，可以让单个线程自旋判断 为了保证比较高效更加兼顾CPU资源，可以切换线程自旋 + 最少睡眠 为了完全兼顾CPU资源不考虑效率问题，可以采用重入锁实现阻塞唤醒 为了完全兼顾CPU资源但考虑一点效率，可以采用重入锁 + GAS唤醒
//完全阻塞的等待策略
//Blocking strategy that uses a lock and condition variable for EventProcessors waiting on a barrier.
//This strategy can be used when throughput and low-latency are not as important as CPU resource.
public final class BlockingWaitStrategy implements WaitStrategy {
private final Lock lock = new ReentrantLock();
private final Condition processorNotifyCondition = lock.newCondition();
@Override
public long waitFor(long sequence, Sequence cursorSequence, Sequence dependentSequence, SequenceBarrier barrier) throws AlertException, InterruptedException {
long availableSequence;
if ((availableSequence = cursorSequence.get()) < sequence) {
lock.lock();
try {
while ((availableSequence = cursorSequence.get()) < sequence) {
barrier.checkAlert();
processorNotifyCondition.await();
}
} finally {
lock.unlock();
}
}
while ((availableSequence = dependentSequence.get()) < sequence) {
barrier.checkAlert();
}
return availableSequence;
}
@Override
public void signalAllWhenBlocking() {
lock.lock();
try {
processorNotifyCondition.signalAll();
} finally {
lock.unlock();
}
}
}
//切换线程自旋的等待策略
//Yielding strategy that uses a Thread.yield() for EventProcessors waiting on a barrier after an initially spinning.
//This strategy is a good compromise between performance and CPU resource without incurring significant latency spikes.
public final class YieldingWaitStrategy implements WaitStrategy {
private static final int SPIN_TRIES = 100;
@Override
public long waitFor(final long sequence, Sequence cursor, final Sequence dependentSequence, final SequenceBarrier barrier) throws AlertException, InterruptedException {
long availableSequence;
int counter = SPIN_TRIES;
while ((availableSequence = dependentSequence.get()) < sequence) {
counter = applyWaitMethod(barrier, counter);
}
return availableSequence;
}
@Override
public void signalAllWhenBlocking() {
}
private int applyWaitMethod(final SequenceBarrier barrier, int counter) throws AlertException {
barrier.checkAlert();
if (0 == counter) {
//切换线程，让另一个线程继续执行自旋操作
Thread.yield();
} else {
--counter;
}
return counter;
}
}
//繁忙自旋的等待策略
//Busy Spin strategy that uses a busy spin loop for EventProcessors waiting on a barrier.
//This strategy will use CPU resource to avoid syscalls which can introduce latency jitter.
//It is best used when threads can be bound to specific CPU cores.
public final class BusySpinWaitStrategy implements WaitStrategy {
@Override
public long waitFor(final long sequence, Sequence cursor, final Sequence dependentSequence, final SequenceBarrier barrier) throws AlertException, InterruptedException {
long availableSequence;
while ((availableSequence = dependentSequence.get()) < sequence) {
barrier.checkAlert();
}
return availableSequence;
}
@Override
public void signalAllWhenBlocking() {
}
}
//轻微阻塞的等待策略(唤醒阻塞线程时避免了并发获取锁)
//Variation of the BlockingWaitStrategy that attempts to elide conditional wake-ups when the lock is uncontended.
//Shows performance improvements on microbenchmarks.
//However this wait strategy should be considered experimental as I have not full proved the correctness of the lock elision code.
public final class LiteBlockingWaitStrategy implements WaitStrategy {
private final Lock lock = new ReentrantLock();
private final Condition processorNotifyCondition = lock.newCondition();
private final AtomicBoolean signalNeeded = new AtomicBoolean(false);
@Override
public long waitFor(long sequence, Sequence cursorSequence, Sequence dependentSequence, SequenceBarrier barrier) throws AlertException, InterruptedException {
long availableSequence;
if ((availableSequence = cursorSequence.get()) < sequence) {
lock.lock();
try {
do {
signalNeeded.getAndSet(true);
if ((availableSequence = cursorSequence.get()) >= sequence) {
break;
}
barrier.checkAlert();
processorNotifyCondition.await();
} while ((availableSequence = cursorSequence.get()) < sequence);
} finally {
lock.unlock();
}
}
while ((availableSequence = dependentSequence.get()) < sequence) {
barrier.checkAlert();
}
return availableSequence;
}
@Override
public void signalAllWhenBlocking() {
if (signalNeeded.getAndSet(false)) {
lock.lock();
try {
processorNotifyCondition.signalAll();
} finally {
lock.unlock();
}
}
}
}
//最小睡眠 + 切换线程的等待策略SleepingWaitStrategy
//Sleeping strategy that initially spins, then uses a Thread.yield(),
//and eventually sleep LockSupport.parkNanos(1) for the minimum number of nanos the OS
//and JVM will allow while the EventProcessors are waiting on a barrier.
//This strategy is a good compromise between performance and CPU resource.
//Latency spikes can occur after quiet periods.
public final class SleepingWaitStrategy implements WaitStrategy {
private static final int DEFAULT_RETRIES = 200;
private final int retries;
public SleepingWaitStrategy() {
this(DEFAULT_RETRIES);
}
public SleepingWaitStrategy(int retries) {
this.retries = retries;
}
@Override
public long waitFor(final long sequence, Sequence cursor, final Sequence dependentSequence, final SequenceBarrier barrier) throws AlertException, InterruptedException {
long availableSequence;
int counter = retries;
while ((availableSequence = dependentSequence.get()) < sequence) {
counter = applyWaitMethod(barrier, counter);
}
return availableSequence;
}
@Override
public void signalAllWhenBlocking() {
}
private int applyWaitMethod(final SequenceBarrier barrier, int counter) throws AlertException {
barrier.checkAlert();
if (counter > 100) {
--counter;
} else if (counter > 0) {
--counter;
Thread.yield();
} else {
LockSupport.parkNanos(1L);
}
return counter;
}
}
4.Disruptor的高性能原因
一.使用了环形结构 + 数组 + 内存预加载
二.使用了单线程写的方式并配合内存屏障
三.消除伪共享(填充缓存行)
四.序号栅栏和序号配合使用来消除锁
五.提供了多种不同性能的等待策略
5.Disruptor高性能之数据结构(内存预加载机制)
(1)RingBuffer使用环形数组来存储元素
(2)采用了内存预加载机制
(1)RingBuffer使用环形数组来存储元素
环形数组可以避免数组扩容和缩容带来的性能损耗。
(2)RingBuffer采用了内存预加载机制
初始化RingBuffer时，会将entries数组里的每一个元素都先new出来。比如RingBuffer的大小设置为8，那么初始化RingBuffer时，就会先将entries数组的8个元素分别指向新new出来的空的Event对象。往RingBuffer填充元素时，只是将对应的Event对象进行赋值。所以RingBuffer中的Event对象是一直存活着的，也就是说它能最小程度减少系统GC频率，从而提升性能。
public class Main {
public static void main(String[] args) {
//参数准备
OrderEventFactory orderEventFactory = new OrderEventFactory();
int ringBufferSize = 4;
ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
//参数一：eventFactory，消息(Event)工厂对象
//参数二：ringBufferSize，容器的长度
//参数三：executor，线程池(建议使用自定义线程池)，RejectedExecutionHandler
//参数四：ProducerType，单生产者还是多生产者
//参数五：waitStrategy，等待策略
//1.实例化Disruptor对象
Disruptor<OrderEvent> disruptor = new Disruptor<OrderEvent>(
orderEventFactory,
ringBufferSize,
executor,
ProducerType.SINGLE,
new BlockingWaitStrategy()
);
//2.添加Event处理器，用于处理事件
//也就是构建Disruptor与消费者的一个关联关系
disruptor.handleEventsWith(new OrderEventHandler());
//3.启动disruptor
disruptor.start();
//4.获取实际存储数据的容器: RingBuffer
RingBuffer<OrderEvent> ringBuffer = disruptor.getRingBuffer();
OrderEventProducer producer = new OrderEventProducer(ringBuffer);
ByteBuffer bb = ByteBuffer.allocate(8);
for (long i = 0; i < 5; i++) {
bb.putLong(0, i);
//向容器中投递数据
producer.sendData(bb);
}
disruptor.shutdown();
executor.shutdown();
}
}
public class Disruptor<T> {
private final RingBuffer<T> ringBuffer;
private final Executor executor;
...
//Create a new Disruptor.
//@param eventFactory the factory to create events in the ring buffer.
//@param ringBufferSize the size of the ring buffer, must be power of 2.
//@param executor an Executor to execute event processors.
//@param producerType the claim strategy to use for the ring buffer.
//@param waitStrategy the wait strategy to use for the ring buffer.
public Disruptor(final EventFactory<T> eventFactory, final int ringBufferSize, final Executor executor, final ProducerType producerType, final WaitStrategy waitStrategy) {
this(RingBuffer.create(producerType, eventFactory, ringBufferSize, waitStrategy), executor);
}
//Private constructor helper
private Disruptor(final RingBuffer<T> ringBuffer, final Executor executor) {
this.ringBuffer = ringBuffer;
this.executor = executor;
}
...
}
//Ring based store of reusable entries containing the data representing an event being exchanged between event producer and EventProcessors.
//@param <E> implementation storing the data for sharing during exchange or parallel coordination of an event.
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
//值为-1
public static final long INITIAL_CURSOR_VALUE = Sequence.INITIAL_VALUE;
protected long p1, p2, p3, p4, p5, p6, p7;
...
//Create a new Ring Buffer with the specified producer type (SINGLE or MULTI)
public static <E> RingBuffer<E> create(ProducerType producerType, EventFactory<E> factory, int bufferSize, WaitStrategy waitStrategy) {
switch (producerType) {
case SINGLE:
return createSingleProducer(factory, bufferSize, waitStrategy);
case MULTI:
return createMultiProducer(factory, bufferSize, waitStrategy);
default:
throw new IllegalStateException(producerType.toString());
}
}
//Create a new single producer RingBuffer with the specified wait strategy.
public static <E> RingBuffer<E> createSingleProducer(EventFactory<E> factory, int bufferSize, WaitStrategy waitStrategy) {
SingleProducerSequencer sequencer = new SingleProducerSequencer(bufferSize, waitStrategy);
return new RingBuffer<E>(factory, sequencer);
}
//Construct a RingBuffer with the full option set.
//@param eventFactory to newInstance entries for filling the RingBuffer
//@param sequencer sequencer to handle the ordering of events moving through the RingBuffer.
RingBuffer(EventFactory<E> eventFactory, Sequencer sequencer) {
super(eventFactory, sequencer);
}
...
}
abstract class RingBufferFields<E> extends RingBufferPad {
private final long indexMask;
//环形数组存储事件消息
private final Object[] entries;
protected final int bufferSize;
//RingBuffer的sequencer属性代表了当前线程对应的生产者
protected final Sequencer sequencer;
...
RingBufferFields(EventFactory<E> eventFactory, Sequencer sequencer) {
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.indexMask = bufferSize - 1;
//初始化数组
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//内存预加载
fill(eventFactory);
}
private void fill(EventFactory<E> eventFactory) {
for (int i = 0; i < bufferSize; i++) {
//设置一个空的数据对象
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
...
}
abstract class RingBufferPad {
protected long p1, p2, p3, p4, p5, p6, p7;
}
6.Disruptor高性能之内核(使用单线程写)
Disruptor的RingBuffer之所以可以做到完全无锁是因为单线程写。离开单线程写，没有任何技术可以做到完全无锁。Redis和Netty等高性能技术框架也是利用单线程写来实现的。
具体就是：单生产者时，固然只有一个生产者线程在写。多生产者时，每个生产者线程都只会写各自获取到的Sequence序号对应的环形数组的元素，从而使得多个生产者线程相互之间不会产生写冲突。
7.Disruptor高性能之系统内存优化(内存屏障)
要正确实现无锁，还需要另外一个关键技术——内存屏障。对应到Java语言，就是valotile变量与Happens Before语义。
内存屏障：Linux的smp_wmb()/smp_rmb()。
8.Disruptor高性能之系统缓存优化(消除伪共享)
CPU缓存是以缓存行(Cache Line)为单位进行存储的。缓存行是2的整数幂个连续字节，一般为32-256个字节，最常见的缓存行大小是64个字节。
当多线程修改互相独立的变量时，如果这些变量共享同一个缓存行，就会对这个缓存行形成竞争，从而无意中影响彼此性能，这就是伪共享。
消除伪共享：利用了空间换时间的思想。
由于代表着一个序号的Sequence其核心字段value是一个long型变量(占8个字节)，所以有可能会出现多个Sequence对象的value变量共享同一个缓存行。因此，需要对Sequence对象的value变量消除伪共享。具体做法就是：对Sequence对象的value变量前后增加7个long型变量。
注意：伪共享与Sequence的静态变量无关，因为静态变量本身就是多个线程共享的，而不是多个线程隔离独立的。
class LhsPadding {
protected long p1, p2, p3, p4, p5, p6, p7;
}
class Value extends LhsPadding {
protected volatile long value;
}
class RhsPadding extends Value {
protected long p9, p10, p11, p12, p13, p14, p15;
}
public class Sequence extends RhsPadding {
static final long INITIAL_VALUE = -1L;
private static final Unsafe UNSAFE;
private static final long VALUE_OFFSET;
static {
UNSAFE = Util.getUnsafe();
try {
VALUE_OFFSET = UNSAFE.objectFieldOffset(Value.class.getDeclaredField("value"));
} catch (final Exception e) {
throw new RuntimeException(e);
}
}
//Create a sequence initialised to -1.
public Sequence() {
this(INITIAL_VALUE);
}
//Create a sequence with a specified initial value.
public Sequence(final long initialValue) {
UNSAFE.putOrderedLong(this, VALUE_OFFSET, initialValue);
}
//Perform a volatile read of this sequence's value.
public long get() {
return value;
}
//Perform an ordered write of this sequence.
//The intent is a Store/Store barrier between this write and any previous store.
public void set(final long value) {
UNSAFE.putOrderedLong(this, VALUE_OFFSET, value);
}
...
}
9.Disruptor高性能之序号获取优化(自旋 + CAS)
生产者投递Event时会使用"long sequence = ringBuffer.next()"获取序号，而序号栅栏SequenceBarrier和会序号Sequence搭配起来一起使用，用来协调和管理消费者和生产者的工作节奏，避免锁的使用。
各个消费者和生产者都持有自己的序号，这些序号需满足如下条件以避免生产者速度过快，将还没来得及消费的消息覆盖。
一.消费者序号数值必须小于生产者序号数值 二.消费者序号数值必须小于其前置消费者的序号数值 三.生产者序号数值不能大于消费者中最小的序号数值
高性能的序号获取优化：为避免生产者每次执行next()获取序号时，都要查询消费者的最小序号，Disruptor采取了自旋 + LockSupport挂起线程 + 缓存最小序号 + CAS来优化。既避免了锁，也尽量在不耗费CPU的情况下提升了性能。
单生产者的情况下，只有一个线程添加元素，此时没必要使用锁。多生产者的情况下，会有多个线程并发获取Sequence序号添加元素，此时会通过自旋 + CAS避免锁。
public class OrderEventProducer {
private RingBuffer<OrderEvent> ringBuffer;
public OrderEventProducer(RingBuffer<OrderEvent> ringBuffer) {
this.ringBuffer = ringBuffer;
}
public void sendData(ByteBuffer data) {
//1.在生产者发送消息时, 首先需要从ringBuffer里获取一个可用的序号
long sequence = ringBuffer.next();
try {
//2.根据这个序号, 找到具体的"OrderEvent"元素
//注意：此时获取的OrderEvent对象是一个没有被赋值的"空对象"
OrderEvent event = ringBuffer.get(sequence);
//3.进行实际的赋值处理
event.setValue(data.getLong(0));
} finally {
//4.提交发布操作
ringBuffer.publish(sequence);
}
}
}
//Ring based store of reusable entries containing the data representing an event being exchanged between event producer and EventProcessors.
//@param <E> implementation storing the data for sharing during exchange or parallel coordination of an event.
public final class RingBuffer<E> extends RingBufferFields<E> implements Cursored, EventSequencer<E>, EventSink<E> {
//值为-1
public static final long INITIAL_CURSOR_VALUE = Sequence.INITIAL_VALUE;
protected long p1, p2, p3, p4, p5, p6, p7;
...
//Increment and return the next sequence for the ring buffer.
//Calls of this method should ensure that they always publish the sequence afterward.
//E.g.
// long sequence = ringBuffer.next();
// try {
// Event e = ringBuffer.get(sequence);
// ...
// } finally {
// ringBuffer.publish(sequence);
// }
//@return The next sequence to publish to.
@Override
public long next() {
return sequencer.next();
}
//Publish the specified sequence.
//This action marks this particular message as being available to be read.
//@param sequence the sequence to publish.
@Override
public void publish(long sequence) {
sequencer.publish(sequence);
}
//Get the event for a given sequence in the RingBuffer.
//This call has 2 uses.
//Firstly use this call when publishing to a ring buffer.
//After calling RingBuffer#next() use this call to get hold of the preallocated event to fill with data before calling RingBuffer#publish(long).
//Secondly use this call when consuming data from the ring buffer.
//After calling SequenceBarrier#waitFor(long) call this method with any value greater than that
//your current consumer sequence and less than or equal to the value returned from the SequenceBarrier#waitFor(long) method.
//@param sequence for the event
//@return the event for the given sequence
@Override
public E get(long sequence) {
//调用父类RingBufferFields的elementAt()方法
return elementAt(sequence);
}
...
}
abstract class RingBufferPad {
protected long p1, p2, p3, p4, p5, p6, p7;
}
abstract class RingBufferFields<E> extends RingBufferPad {
...
private static final Unsafe UNSAFE = Util.getUnsafe();
private final long indexMask;
//环形数组存储事件消息
private final Object[] entries;
protected final int bufferSize;
//RingBuffer的sequencer属性代表了当前线程对应的生产者
protected final Sequencer sequencer;
RingBufferFields(EventFactory<E> eventFactory, Sequencer sequencer) {
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.indexMask = bufferSize - 1;
//初始化数组
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//内存预加载
fill(eventFactory);
}
private void fill(EventFactory<E> eventFactory) {
for (int i = 0; i < bufferSize; i++) {
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
protected final E elementAt(long sequence) {
return (E) UNSAFE.getObject(entries, REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT));
}
...
}
public abstract class AbstractSequencer implements Sequencer {
private static final AtomicReferenceFieldUpdater<AbstractSequencer, Sequence[]> SEQUENCE_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(AbstractSequencer.class, Sequence[].class, "gatingSequences");
//环形数组的大小
protected final int bufferSize;
//等待策略
protected final WaitStrategy waitStrategy;
//当前生产者的进度
protected final Sequence cursor = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
//每一个Sequence都对应着一个消费者(一个EventHandler或者一个WorkHandler)
//这些Sequence会通过SEQUENCE_UPDATER在执行Disruptor的handleEventsWith()等方法时，
//由RingBuffer的addGatingSequences()方法进行添加
protected volatile Sequence[] gatingSequences = new Sequence[0];
...
//Create with the specified buffer size and wait strategy.
//@param bufferSize The total number of entries, must be a positive power of 2.
//@param waitStrategy
public AbstractSequencer(int bufferSize, WaitStrategy waitStrategy) {
if (bufferSize < 1) {
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
if (Integer.bitCount(bufferSize) != 1) {
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
this.bufferSize = bufferSize;
this.waitStrategy = waitStrategy;
}
...
}
abstract class SingleProducerSequencerPad extends AbstractSequencer {
protected long p1, p2, p3, p4, p5, p6, p7;
public SingleProducerSequencerPad(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
}
abstract class SingleProducerSequencerFields extends SingleProducerSequencerPad {
public SingleProducerSequencerFields(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
//表示生产者的当前序号，值为-1
protected long nextValue = Sequence.INITIAL_VALUE;
//表示消费者的最小序号，值为-1
protected long cachedValue = Sequence.INITIAL_VALUE;
}
public final class SingleProducerSequencer extends SingleProducerSequencerFields {
protected long p1, p2, p3, p4, p5, p6, p7;
//Construct a Sequencer with the selected wait strategy and buffer size.
//@param bufferSize the size of the buffer that this will sequence over.
//@param waitStrategy for those waiting on sequences.
public SingleProducerSequencer(int bufferSize, WaitStrategy waitStrategy) {
super(bufferSize, waitStrategy);
}
...
@Override
public long next() {
return next(1);
}
@Override
public long next(int n) {
//Sequence的初始化值为-1
if (n < 1) {
throw new IllegalArgumentException("n must be > 0");
}
//nextValue指的是当前Sequence
//this.nextValue为SingleProducerSequencerFields的变量
//第一次调用next()方法时，nextValue = -1
//第二次调用next()方法时，nextValue = 0
//第三次调用next()方法时，nextValue = 1
//第四次调用next()方法时，nextValue = 2
//第五次调用next()方法时，nextValue = 3
long nextValue = this.nextValue;
//第一次调用next()方法时，nextSequence = -1 + 1 = 0
//第二次调用next()方法时，nextSequence = 0 + 1 = 1
//第三次调用next()方法时，nextSequence = 1 + 1 = 2
//第四次调用next()方法时，nextSequence = 2 + 1 = 3
//第五次调用next()方法时，nextSequence = 3 + 1 = 4
long nextSequence = nextValue + n;
//wrapPoint会用来判断生产者序号是否绕过RingBuffer的环
//如果wrapPoint是负数，则表示还没绕过RingBuffer的环
//如果wrapPoint是非负数，则表示已经绕过RingBuffer的环
//假设bufferSize = 3，那么：
//第一次调用next()方法时，wrapPoint = 0 - 3 = -3，还没绕过RingBuffer的环
//第二次调用next()方法时，wrapPoint = 1 - 3 = -2，还没绕过RingBuffer的环
//第三次调用next()方法时，wrapPoint = 2 - 3 = -1，还没绕过RingBuffer的环
//第四次调用next()方法时，wrapPoint = 3 - 3 = 0，已经绕过RingBuffer的环
//第五次调用next()方法时，wrapPoint = 4 - 3 = 1，已经绕过RingBuffer的环
long wrapPoint = nextSequence - bufferSize;
//cachedGatingSequence是用来将消费者的最小消费序号缓存起来
//这样就不用每次执行next()方法都要去获取消费者的最小消费序号
//第一次调用next()方法时，cachedGatingSequence = -1
//第二次调用next()方法时，cachedGatingSequence = -1
//第三次调用next()方法时，cachedGatingSequence = -1
//第四次调用next()方法时，cachedGatingSequence = -1
//第五次调用next()方法时，cachedGatingSequence = 1
long cachedGatingSequence = this.cachedValue;
//第四次调用next()方法时，wrapPoint大于cachedGatingSequence，执行条件中的逻辑
if (wrapPoint > cachedGatingSequence || cachedGatingSequence > nextValue) {
//最小的消费者序号
long minSequence;
//自旋操作：
//Util.getMinimumSequence(gatingSequences, nextValue)的含义就是找到消费者中最小的序号值
//如果wrapPoint > 消费者中最小的序号，那么生产者线程就需要进行阻塞
//即如果生产者序号 > 消费者中最小的序号，那么就挂起并进行自旋操作
//第四次调用next()方法时，nextValue = 2，wrapPoint = 0，gatingSequences里面的消费者序号如果还没消费(即-1)，则要挂起
while (wrapPoint > (minSequence = Util.getMinimumSequence(gatingSequences, nextValue))) {
//TODO: Use waitStrategy to spin?
LockSupport.parkNanos(1L);
}
//cachedValue接收了消费者的最小序号
//第四次调用next()方法时，假设消费者的最小序号minSequence为1，则cachedValue = 1
this.cachedValue = minSequence;
}
//第一次调用完next()方法时，nextValue会变为0
//第二次调用完next()方法时，nextValue会变为1
//第三次调用完next()方法时，nextValue会变为2
//第四次调用完next()方法时，nextValue会变为3
//第五次调用完next()方法时，nextValue会变为4
this.nextValue = nextSequence;
//第一次调用next()方法时，返回的nextSequence = 0
//第二次调用next()方法时，返回的nextSequence = 1
//第三次调用next()方法时，返回的nextSequence = 2
//第四次调用next()方法时，返回的nextSequence = 3
//第五次调用next()方法时，返回的nextSequence = 4
return nextSequence;
}
@Override
public void publish(long sequence) {
//设置当前生产者的sequence
cursor.set(sequence);
//通过等待策略通知阻塞的消费者
waitStrategy.signalAllWhenBlocking();
}
...
}
public final class Util {
...
//Get the minimum sequence from an array of {@link com.lmax.disruptor.Sequence}s.
//@param sequences to compare.
//@param minimum an initial default minimum. If the array is empty this value will be returned.
//@return the smaller of minimum sequence value found in sequences and minimum; minimum if sequences is empty
public static long getMinimumSequence(final Sequence[] sequences, long minimum) {
for (int i = 0, n = sequences.length; i < n; i++) {
long value = sequences[i].get();
minimum = Math.min(minimum, value);
}
return minimum;
}
...
}
public final class MultiProducerSequencer extends AbstractSequencer {
...
@Override
public long next() {
return next(1);
}
@Override
public long next(int n) {
if (n < 1) {
throw new IllegalArgumentException("n must be > 0");
}
long current;
long next;
do {
//获取当前生产者的序号
current = cursor.get();
next = current + n;
//wrapPoint会用来判断生产者序号是否绕过RingBuffer的环
//如果wrapPoint是负数，则表示还没绕过RingBuffer的环
//如果wrapPoint是非负数，则表示已经绕过RingBuffer的环
long wrapPoint = next - bufferSize;
//cachedGatingSequence是用来将消费者的最小消费序号缓存起来
//这样就不用每次执行next()方法都要去获取消费者的最小消费序号
long cachedGatingSequence = gatingSequenceCache.get();
if (wrapPoint > cachedGatingSequence || cachedGatingSequence > current) {
//gatingSequence表示的是消费者的最小序号
long gatingSequence = Util.getMinimumSequence(gatingSequences, current);
if (wrapPoint > gatingSequence) {
//TODO, should we spin based on the wait strategy?
LockSupport.parkNanos(1);
continue;
}
gatingSequenceCache.set(gatingSequence);
} else if (cursor.compareAndSet(current, next)) {
break;
}
} while (true);
return next;
}
...
}
后端技术栈的基础修养 文章被收录于专栏
详细介绍后端技术栈的基础内容，包括但不限于：MySQL原理和优化、Redis原理和应用、JVM和G1原理和优化、RocketMQ原理应用及源码、Kafka原理应用及源码、ElasticSearch原理应用及源码、JUC源码、Netty源码、zk源码、Dubbo源码、Spring源码、Spring Boot源码、SCA源码、分布式锁源码、分布式事务、分库分表和TiDB、大型商品系统、大型订单系统等
