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/**
 * Strategy employed for making {@link EventProcessor}s wait on a cursor {@link Sequence}.
 */
public interface WaitStrategy
{
    /**
     * Wait for the given sequence to be available.  It is possible for this method to return a value
     * less than the sequence number supplied depending on the implementation of the WaitStrategy.  A common
     * use for this is to signal a timeout.  Any EventProcessor that is using a WaitStrategy to get notifications
     * about message becoming available should remember to handle this case.  The {@link BatchEventProcessor} explicitly
     * handles this case and will signal a timeout if required.
     * 等待给定的序列可用。这个方法有可能返回一个小于所提供序列号的值，这取决于等待策略的实现。常用的方法是发出超时信号。
     * 任何正在使用"等待策略"的事件处理器都应该记得处理这种情况。 {@linkBatchEventProcessor}显式处理这种情况，如果需要，将会发出超时信号。
     *
     * @param sequence          to be waited on.
     * @param cursor            the main sequence from ringbuffer. Wait/notify strategies will
     *                          need this as it's the only sequence that is also notified upon update.
     * @param dependentSequence on which to wait.
     * @param barrier           the processor is waiting on.
     * @return the sequence that is available which may be greater than the requested sequence.
     * @throws AlertException       if the status of the Disruptor has changed.
     * @throws InterruptedException if the thread is interrupted.
     * @throws TimeoutException if a timeout occurs before waiting completes (not used by some strategies)
     */
    long waitFor(long sequence, Sequence cursor, Sequence dependentSequence, SequenceBarrier barrier)
        throws AlertException, InterruptedException, TimeoutException;

    /**
     * Implementations should signal the waiting {@link EventProcessor}s that the cursor has advanced.
     * 当发布事件成功后会调用这个方法来通知等待的事件处理者序列可用了。
     */
    void signalAllWhenBlocking();
}

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/**
 * Blocking strategy that uses a lock and condition variable for {@link EventProcessor}s waiting on a barrier.
 * 阻塞策略使用一个锁和条件变量的{@link EventProcessor}等待一个障碍。
 * <p>
 * This strategy can be used when throughput and low-latency are not as important as CPU resource.
 * 当吞吐量和低延迟不如CPU资源重要时，可以使用此策略。
 */
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 (cursorSequence.get() < sequence)
        {
            lock.lock();
            try
            {
                while (cursorSequence.get() < sequence)
                {
                    barrier.checkAlert();
                    processorNotifyCondition.await();
                }
            }
            finally
            {
                lock.unlock();
            }
        }
        //再次检测，避免事件处理器关闭的情况。
        while ((availableSequence = dependentSequence.get()) < sequence)
        {
            barrier.checkAlert();
            ThreadHints.onSpinWait();
        }

        return availableSequence;
    }

    @Override
    public void signalAllWhenBlocking()
    {
        lock.lock();
        try
        {
            processorNotifyCondition.signalAll();
        }
        finally
        {
            lock.unlock();
        }
    }

    @Override
    public String toString()
    {
        return "BlockingWaitStrategy{" +
            "processorNotifyCondition=" + processorNotifyCondition +
            '}';
    }
}

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/**
 * Busy Spin strategy that uses a busy spin loop for {@link com.lmax.disruptor.EventProcessor}s waiting on a barrier.
 * 繁忙的自旋策略，使用繁忙的自旋循环来等待屏障上的{@link com.lmax.disruptor.EventProcessor}。
 * <p>
 * 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.
 * 这个策略将使用CPU资源来避免引起延迟抖动的系统调用。当线程可以绑定到特定的CPU内核时，最好使用它。
 */
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();
            ThreadHints.onSpinWait();
        }

        return availableSequence;
    }

    @Override
    public void signalAllWhenBlocking()
    {
    }
}

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/**
 * Variation of the {@link 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.
 * 当锁被锁定时，尝试忽略条件唤醒的{@link BlockingWaitStrategy}的变化。显示microbenchmarks的性能改进。然而，
 * 这个等待策略应该被认为是实验性的，因为我没有充分证明锁码的正确性。
 */
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 (cursorSequence.get() < sequence)
        {
            lock.lock();

            try
            {
                do
                {
                    signalNeeded.getAndSet(true);

                    if (cursorSequence.get() >= sequence)
                    {
                        break;
                    }

                    barrier.checkAlert();
                    processorNotifyCondition.await();
                }
                while (cursorSequence.get() < sequence);
            }
            finally
            {
                lock.unlock();
            }
        }

        while ((availableSequence = dependentSequence.get()) < sequence)
        {
            barrier.checkAlert();
            ThreadHints.onSpinWait();
        }

        return availableSequence;
    }

    @Override
    public void signalAllWhenBlocking()
    {
        if (signalNeeded.getAndSet(false))
        {
            lock.lock();
            try
            {
                processorNotifyCondition.signalAll();
            }
            finally
            {
                lock.unlock();
            }
        }
    }

    @Override
    public String toString()
    {
        return "LiteBlockingWaitStrategy{" +
            "processorNotifyCondition=" + processorNotifyCondition +
            '}';
    }
}

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/**
 * Sleeping strategy that initially spins, then uses a Thread.yield(), and
 * eventually sleep (<code>LockSupport.parkNanos(1)</code>) for the minimum
 * number of nanos the OS and JVM will allow while the
 * {@link com.lmax.disruptor.EventProcessor}s are waiting on a barrier.
 *  睡眠策略,最初自旋转次数，然后使用Thread.yield（），最终睡眠（LockSupport.parkNanos（1））操作系统和
 *  JVM允许的最小*{@link com.lmax.disruptor.EventProcessor}正在等待屏障。
 * <p>
 * This strategy is a good compromise between performance and CPU resource.
 * Latency spikes can occur after quiet periods.
 * 这个策略是性能和CPU资源之间的一个很好的折中。可能会出现延迟峰值。
 */
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;
    }
}

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public class TimeoutBlockingWaitStrategy implements WaitStrategy
{
    private final Lock lock = new ReentrantLock();
    private final Condition processorNotifyCondition = lock.newCondition();
    private final long timeoutInNanos;

    public TimeoutBlockingWaitStrategy(final long timeout, final TimeUnit units)
    {
        timeoutInNanos = units.toNanos(timeout);
    }

    @Override
    public long waitFor(
        final long sequence,
        final Sequence cursorSequence,
        final Sequence dependentSequence,
        final SequenceBarrier barrier)
        throws AlertException, InterruptedException, TimeoutException
    {
        long nanos = timeoutInNanos;

        long availableSequence;
        if (cursorSequence.get() < sequence)
        {
            lock.lock();
            try
            {
                while (cursorSequence.get() < sequence)
                {
                    barrier.checkAlert();
                    nanos = processorNotifyCondition.awaitNanos(nanos);
                    if (nanos <= 0)
                    {
                        throw TimeoutException.INSTANCE;
                    }
                }
            }
            finally
            {
                lock.unlock();
            }
        }

        while ((availableSequence = dependentSequence.get()) < sequence)
        {
            barrier.checkAlert();
        }

        return availableSequence;
    }

    @Override
    public void signalAllWhenBlocking()
    {
        lock.lock();
        try
        {
            processorNotifyCondition.signalAll();
        }
        finally
        {
            lock.unlock();
        }
    }

    @Override
    public String toString()
    {
        return "TimeoutBlockingWaitStrategy{" +
            "processorNotifyCondition=" + processorNotifyCondition +
            '}';
    }
}

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/**
 * Yielding strategy that uses a Thread.yield() for {@link com.lmax.disruptor.EventProcessor}s waiting on a barrier
 * after an initially spinning.
 * 让出调度策略 在初始旋转之后，为使用Thread.yield（）的{@link com.lmax.disruptor.EventProcessor}等待障碍的产生策略。
 * <p>
 * This strategy is a good compromise between performance and CPU resource without incurring significant latency spikes.
 * 这一策略是性能和CPU资源之间的一个很好的折中，不会引起显著的延迟峰值。
 */
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)
        {
            Thread.yield();
        }
        else
        {
            --counter;
        }

        return counter;
    }
}

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/**
 * <p>Phased wait strategy for waiting {@link EventProcessor}s on a barrier.</p>
 * 分阶段等策略
 *
 * <p>This strategy can be used when throughput and low-latency are not as important as CPU resource.
 * Spins, then yields, then waits using the configured fallback WaitStrategy.</p>
 * 当吞吐量和低延迟不如CPU资源重要时，可以使用此策略。然后旋转，然后yields，然后使用配置的回退等待策略等待
 */
public final class PhasedBackoffWaitStrategy implements WaitStrategy
{
    private static final int SPIN_TRIES = 10000;
    private final long spinTimeoutNanos;
    private final long yieldTimeoutNanos;
    private final WaitStrategy fallbackStrategy;

    public PhasedBackoffWaitStrategy(
        long spinTimeout,
        long yieldTimeout,
        TimeUnit units,
        WaitStrategy fallbackStrategy)
    {
        this.spinTimeoutNanos = units.toNanos(spinTimeout);
        this.yieldTimeoutNanos = spinTimeoutNanos + units.toNanos(yieldTimeout);
        this.fallbackStrategy = fallbackStrategy;
    }

    /**
     * Construct {@link PhasedBackoffWaitStrategy} with fallback to {@link BlockingWaitStrategy}
     *
     * @param spinTimeout The maximum time in to busy spin for.
     * @param yieldTimeout The maximum time in to yield for.
     * @param units Time units used for the timeout values.
     * @return The constructed wait strategy.
     */
    public static PhasedBackoffWaitStrategy withLock(
        long spinTimeout,
        long yieldTimeout,
        TimeUnit units)
    {
        return new PhasedBackoffWaitStrategy(
            spinTimeout, yieldTimeout,
            units, new BlockingWaitStrategy());
    }

    /**
     * Construct {@link PhasedBackoffWaitStrategy} with fallback to {@link LiteBlockingWaitStrategy}
     *
     * @param spinTimeout The maximum time in to busy spin for.
     * @param yieldTimeout The maximum time in to yield for.
     * @param units Time units used for the timeout values.
     * @return The constructed wait strategy.
     */
    public static PhasedBackoffWaitStrategy withLiteLock(
        long spinTimeout,
        long yieldTimeout,
        TimeUnit units)
    {
        return new PhasedBackoffWaitStrategy(
            spinTimeout, yieldTimeout,
            units, new LiteBlockingWaitStrategy());
    }

    /**
     * Construct {@link PhasedBackoffWaitStrategy} with fallback to {@link SleepingWaitStrategy}
     *
     * @param spinTimeout The maximum time in to busy spin for.
     * @param yieldTimeout The maximum time in to yield for.
     * @param units Time units used for the timeout values.
     * @return The constructed wait strategy.
     */
    public static PhasedBackoffWaitStrategy withSleep(
        long spinTimeout,
        long yieldTimeout,
        TimeUnit units)
    {
        return new PhasedBackoffWaitStrategy(
            spinTimeout, yieldTimeout,
            units, new SleepingWaitStrategy(0));
    }

    @Override
    public long waitFor(long sequence, Sequence cursor, Sequence dependentSequence, SequenceBarrier barrier)
        throws AlertException, InterruptedException, TimeoutException
    {
        long availableSequence;
        long startTime = 0;
        int counter = SPIN_TRIES;

        do
        {
            if ((availableSequence = dependentSequence.get()) >= sequence)
            {
                return availableSequence;
            }

            if (0 == --counter)
            {
                if (0 == startTime)
                {
                    startTime = System.nanoTime();
                }
                else
                {
                    long timeDelta = System.nanoTime() - startTime;
                    if (timeDelta > yieldTimeoutNanos)
                    {
                        return fallbackStrategy.waitFor(sequence, cursor, dependentSequence, barrier);
                    }
                    else if (timeDelta > spinTimeoutNanos)
                    {
                        Thread.yield();
                    }
                }
                counter = SPIN_TRIES;
            }
        }
        while (true);
    }

    @Override
    public void signalAllWhenBlocking()
    {
        fallbackStrategy.signalAllWhenBlocking();
    }
}