RingBuffer类是Disruptor核心的数据结构类。它是一个环状的Buffer,上面的槽(slot)可以保存一个个Event。下面是Disruptor中RingBuffer类继承关系:
除了实现之前提到过的Sequenced和Cursored接口,这里还涉及到了DataProvider这个接口。
public interface DataProvider
{
T get(long sequence);
}
它只有一个方法get,这个方法就是获取某个sequence对应的对象,对象类型在这里是抽象的(T)。这个方法对于RingBuffer会在两个地方调用,第一个是在生产时,这个Event对象需要被生产者获取往里面填充数据。第二个是在消费时,获取这个Event对象用于消费。
EventSequencer接口没有自己的方法,只是为了将Sequencer和DataProvider合起来。
EventSink代表RingBuffer是一个以Event槽为基础的数据结构。同时实现EventSequencer和EventSink代表RingBuffer是一个以Event槽为基础元素保存的数据结构。
EventSink接口的主要方法都是发布Event,发布一个Event的流程是:申请下一个Sequence->申请成功则获取对应槽的Event->初始化并填充对应槽的Event->发布Event。这里,初始化,填充Event是通过实现EventTranslator,EventTranslatorOneArg,EventTranslatorTwoArg,EventTranslatorThreeArg,EventTranslatorVararg这些EventTranslator来做的。我们看下EventTranslator,EventTranslatorOneArg和EventTranslatorVararg的源码:
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(final T event, long sequence);
}
public interface EventTranslatorOneArg<T, A>
{
/**
* 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.
* @param arg0 The first user specified argument to the translator
*/
void translateTo(final T event, long sequence, final A arg0);
}
public interface EventTranslatorVararg<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.
* @param args The array of user arguments.
*/
void translateTo(final T event, long sequence, final Object... args);
}
他们由生产者用户实现,将Event初始化并填充。在发布一条Event的时候,这些Translator的translate方法会被调用。在translate方法初始化并填充Event。对于EventTranslator,translate方法只接受Event和Sequence作为参数,对于其他的,都还会接受一个或多个参数用来初始化并填充Event。
EventSink接口是用来发布Event的,在发布的同时,调用绑定的Translator来初始化并填充Event。EventSink接口的大部分方法接受不同的Translator来处理Event:
public interface EventSink<E> {
/**
* 申请下一个Sequence->申请成功则获取对应槽的Event->利用translator初始化并填充对应槽的Event->发布Event
* @param translator translator用户实现,用于初始化Event,这里是不带参数Translator
*/
void publishEvent(EventTranslator translator);
/**
* 尝试申请下一个Sequence->申请成功则获取对应槽的Event->利用translator初始化并填充对应槽的Event->发布Event
* 若空间不足,则立即失败返回
* @param translator translator用户实现,用于初始化Event,这里是不带参数Translator
* @return 成功true,失败false
*/
boolean tryPublishEvent(EventTranslator translator);
void publishEvent(EventTranslatorOneArg translator, A arg0);
boolean tryPublishEvent(EventTranslatorOneArg translator, A arg0);
void publishEvent(EventTranslatorTwoArg translator, A arg0, B arg1);
boolean tryPublishEvent(EventTranslatorTwoArg translator, A arg0, B arg1);
void publishEvent(EventTranslatorThreeArg translator, A arg0, B arg1, C arg2);
boolean tryPublishEvent(EventTranslatorThreeArg translator, A arg0, B arg1, C arg2);
void publishEvent(EventTranslatorVararg translator, Object... args);
boolean tryPublishEvent(EventTranslatorVararg translator, Object... args);
/**
* 包括申请多个Sequence->申请成功则获取对应槽的Event->利用每个translator初始化并填充每个对应槽的Event->发布Event
* @param translators
*/
void publishEvents(EventTranslator[] translators);
void publishEvents(EventTranslator[] translators, int batchStartsAt, int batchSize);
boolean tryPublishEvents(EventTranslator[] translators);
boolean tryPublishEvents(EventTranslator[] translators, int batchStartsAt, int batchSize);
void publishEvents(EventTranslatorOneArg translator, A[] arg0);
void publishEvents(EventTranslatorOneArg translator, int batchStartsAt, int batchSize, A[] arg0);
boolean tryPublishEvents(EventTranslatorOneArg translator, A[] arg0);
boolean tryPublishEvents(EventTranslatorOneArg translator, int batchStartsAt, int batchSize, A[] arg0);
void publishEvents(EventTranslatorTwoArg translator, A[] arg0, B[] arg1);
void publishEvents(
EventTranslatorTwoArg translator, int batchStartsAt, int batchSize, A[] arg0,
B[] arg1);
boolean tryPublishEvents(EventTranslatorTwoArg translator, A[] arg0, B[] arg1);
boolean tryPublishEvents(
EventTranslatorTwoArg translator, int batchStartsAt, int batchSize,
A[] arg0, B[] arg1);
void publishEvents(EventTranslatorThreeArg translator, A[] arg0, B[] arg1, C[] arg2);
void publishEvents(
EventTranslatorThreeArg translator, int batchStartsAt, int batchSize,
A[] arg0, B[] arg1, C[] arg2);
boolean tryPublishEvents(EventTranslatorThreeArg translator, A[] arg0, B[] arg1, C[] arg2);
boolean tryPublishEvents(
EventTranslatorThreeArg translator, int batchStartsAt,
int batchSize, A[] arg0, B[] arg1, C[] arg2);
void publishEvents(EventTranslatorVararg translator, Object[]... args);
void publishEvents(EventTranslatorVararg translator, int batchStartsAt, int batchSize, Object[]... args);
boolean tryPublishEvents(EventTranslatorVararg translator, Object[]... args);
boolean tryPublishEvents(EventTranslatorVararg translator, int batchStartsAt, int batchSize, Object[]... args);
}
接下来到我们的主要环节,RingBuffer类。与之前相似,RingBuffer也是做了缓冲行填充。
RingBuffer类中保存了整个RingBuffer每个槽(entry或者slot)的Event对象,对应的field是private final Object[] entries;
,这些对象只在RingBuffer初始化时被建立,之后就是修改这些对象(初始化Event和填充Event),并不会重新建立新的对象。RingBuffer可以有多生产者和消费者,所以这个entries会被多线程访问频繁的,但不会修改(因为不会重新建立新的对象,这个数组保存的是对对象的具体引用,所以不会变)。但是我们要避免他们和被修改的对象读取到同一个缓存行,避免缓存行失效重新读取。
我们看源代码:
abstract class RingBufferPad
{
protected long p1, p2, p3, p4, p5, p6, p7;
}
abstract class RingBufferFields extends RingBufferPad
{
//Buffer数组填充
private static final int BUFFER_PAD;
//Buffer数组起始基址
private static final long REF_ARRAY_BASE;
//2^n=每个数组对象引用所占空间,这个n就是REF_ELEMENT_SHIFT
private static final int REF_ELEMENT_SHIFT;
private static final Unsafe UNSAFE = Util.getUnsafe();
static
{
//Object数组引用长度,32位为4字节,64位为8字节
final int scale = UNSAFE.arrayIndexScale(Object[].class);
if (4 == scale)
{
REF_ELEMENT_SHIFT = 2;
}
else if (8 == scale)
{
REF_ELEMENT_SHIFT = 3;
}
else
{
throw new IllegalStateException("Unknown pointer size");
}
//需要填充128字节,缓存行长度一般是128字节
BUFFER_PAD = 128 / scale;
// Including the buffer pad in the array base offset
REF_ARRAY_BASE = UNSAFE.arrayBaseOffset(Object[].class) + (BUFFER_PAD << REF_ELEMENT_SHIFT);
}
private final long indexMask;
private final Object[] entries;
protected final int bufferSize;
protected final Sequencer sequencer;
RingBufferFields(
EventFactory eventFactory,
Sequencer sequencer)
{
this.sequencer = sequencer;
this.bufferSize = sequencer.getBufferSize();
//保证buffer大小不小于1
if (bufferSize < 1)
{
throw new IllegalArgumentException("bufferSize must not be less than 1");
}
//保证buffer大小为2的n次方
if (Integer.bitCount(bufferSize) != 1)
{
throw new IllegalArgumentException("bufferSize must be a power of 2");
}
//m % 2^n <=> m & (2^n - 1)
this.indexMask = bufferSize - 1;
/**
* 结构:缓存行填充,避免频繁访问的任一entry与另一被修改的无关变量写入同一缓存行
* --------------
* * 数组头 * BASE
* * Padding * 128字节
* * reference1 * SCALE
* * reference2 * SCALE
* * reference3 * SCALE
* ..........
* * Padding * 128字节
* --------------
*/
this.entries = new Object[sequencer.getBufferSize() + 2 * BUFFER_PAD];
//利用eventFactory初始化RingBuffer的每个槽
fill(eventFactory);
}
private void fill(EventFactory eventFactory)
{
for (int i = 0; i < bufferSize; i++)
{
entries[BUFFER_PAD + i] = eventFactory.newInstance();
}
}
@SuppressWarnings("unchecked")
protected final E elementAt(long sequence)
{
return (E) UNSAFE.getObject(entries, REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT));
}
}
注释中提到对于entries数组的缓存行填充,申请的数组大小为实际需要大小加上2 * BUFFER_PAD,所占空间就是2*128字节。由于数组中的元素经常访问,所以将数组中的实际元素两边各加上128字节的padding防止false sharing。
所以,初始化RingBuffer内所有对象时,从下标BUFFER_PAD开始,到BUFFER_PAD+bufferSize-1为止。取出某一sequence的对象,也是BUFFER_PAD开始算0,这里的:return (E) UNSAFE.getObject(entries, REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT));
代表取出entries对象,地址为REF_ARRAY_BASE + ((sequence & indexMask) << REF_ELEMENT_SHIFT)的对象。这里是个对象引用,地址是以REF_ARRAY_BASE 为基址(数组基址+数组头+引用偏移),每个引用占用2^REF_ELEMENT_SHIFT个字节,sequence 对bufferSize取模乘以2^REF_ELEMENT_SHIFT。
接下来看可以供用户调用的具体的构造方法,RingBuffer在Disruptor包外部不能直接调用其构造方法,用户只能用静态方法创建:
/**
* 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.
* @throws IllegalArgumentException if bufferSize is less than 1 or not a power of 2
*/
RingBuffer(
EventFactory eventFactory,
Sequencer sequencer)
{
super(eventFactory, sequencer);
}
/**
* Create a new multiple producer RingBuffer with the specified wait strategy.
*
* @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.
* @throws IllegalArgumentException if bufferSize is less than 1 or not a power of 2
* @see MultiProducerSequencer
*/
public static RingBuffer createMultiProducer(
EventFactory factory,
int bufferSize,
WaitStrategy waitStrategy)
{
MultiProducerSequencer sequencer = new MultiProducerSequencer(bufferSize, waitStrategy);
return new RingBuffer(factory, sequencer);
}
/**
* Create a new multiple producer RingBuffer using the default wait strategy {@link BlockingWaitStrategy}.
*
* @param factory used to create the events within the ring buffer.
* @param bufferSize number of elements to create within the ring buffer.
* @throws IllegalArgumentException if bufferSize is less than 1 or not a power of 2
* @see MultiProducerSequencer
*/
public static RingBuffer createMultiProducer(EventFactory factory, int bufferSize)
{
return createMultiProducer(factory, bufferSize, new BlockingWaitStrategy());
}
/**
* Create a new single producer RingBuffer with the specified wait strategy.
*
* @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.
* @throws IllegalArgumentException if bufferSize is less than 1 or not a power of 2
* @see SingleProducerSequencer
*/
public static RingBuffer createSingleProducer(
EventFactory factory,
int bufferSize,
WaitStrategy waitStrategy)
{
SingleProducerSequencer sequencer = new SingleProducerSequencer(bufferSize, waitStrategy);
return new RingBuffer(factory, sequencer);
}
/**
* Create a new single producer RingBuffer using the default wait strategy {@link BlockingWaitStrategy}.
*
* @param factory used to create the events within the ring buffer.
* @param bufferSize number of elements to create within the ring buffer.
* @throws IllegalArgumentException if bufferSize is less than 1 or not a power of 2
* @see MultiProducerSequencer
*/
public static RingBuffer createSingleProducer(EventFactory factory, int bufferSize)
{
return createSingleProducer(factory, bufferSize, new BlockingWaitStrategy());
}
/**
* Create a new Ring Buffer with the specified producer type (SINGLE or MULTI)
*
* @param producerType producer type to use {@link 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.
* @throws IllegalArgumentException if bufferSize is less than 1 or not a power of 2
*/
public static RingBuffer create(
ProducerType producerType,
EventFactory 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());
}
}
用户组装一个RingBuffer需要如下元素:实现EventFactory的Event的工厂,实现Sequencer的生产者,等待策略waitStrategy还有bufferSize。
接下来里面方法的实现都比较简单,这里不再赘述