JDK1.8中CountDownLatch 源码(注释已经翻译成中文)
JDK1.8中CountDownLatch 源码(注释已经翻译成中文)
凯哥Java
发布于 2022-12-16 13:51:05
发布于 2022-12-16 13:51:05
以下是countdownlatch源码。注释已经翻译成中文：
package?java.util.concurrent;
import?java.util.concurrent.locks.AbstractQueuedSynchronizer;
/**
?*?A?synchronization?aid?that?allows?one?or?more?threads?to?wait?until??a?set?of?operations?being?performed?in?other?threads?completes.
?*一种同步辅助程序，允许一个或多个线程等待在其它线程中执行的一组操作完成。
?*
?*?<p>A?{@code?CountDownLatch}?is?initialized?with?a?given?<em>count</em>.
?*?The?{@link?#await?await}?methods?block?until?the?current?count?reaches
?*?zero?due?to?invocations?of?the?{@link?#countDown}?method,?after?which
?*?all?waiting?threads?are?released?and?any?subsequent?invocations?of
?*?{@link?#await?await}?return?immediately.??This?is?a?one-shot?phenomenon
?*?--?the?count?cannot?be?reset.??If?you?need?a?version?that?resets?the
?*?count,?consider?using?a?{@link?CyclicBarrier}.
?*?用给定的count之来初始化countDownLatch对象。调用?countDown方法直到当前count减少到0的时候，await方法就会被释放掉(不在阻塞)
?*?这是一次性的倒计时器，无法重置(reset)计数器.如果你需要重置count的话，可以使用CyclicBarrier这个对象
?*
?*?<p>A?{@code?CountDownLatch}?is?a?versatile?synchronization?tool
?*?and?can?be?used?for?a?number?of?purposes.??A
?*?{@code?CountDownLatch}?initialized?with?a?count?of?one?serves?as?a
?*?simple?on/off?latch,?or?gate:?all?threads?invoking?{@link?#await?await}
?*?wait?at?the?gate?until?it?is?opened?by?a?thread?invoking?{@link
?*?#countDown}.??A?{@code?CountDownLatch}?initialized?to?<em>N</em>
?*?can?be?used?to?make?one?thread?wait?until?<em>N</em>?threads?have
?*?completed?some?action,?or?some?action?has?been?completed?N?times.
?*CountDownLatch是一个通用的同步工具，适用于很多场景。
?*CountDownLatch在初始化的时候，计数器设置为1的时候，可以作为一个简单的开关。
?*所有调用await方法的线程都在等待着。直到调用countDown方法的时候，线程才不会继续等待。
?*初始化一个计数器为N的CountDownLatch对象的含义：有可能是一个线程在等待其他N个线程完成某一个操作
?*或者是某个操作完成N次
?*
?*?<p>A?useful?property?of?a?{@code?CountDownLatch}?is?that?it
?*?doesn't?require?that?threads?calling?{@code?countDown}?wait?for
?*?the?count?to?reach?zero?before?proceeding,?it?simply?prevents?any
?*?thread?from?proceeding?past?an?{@link?#await?await}?until?all
?*?threads?could?pass.
?*
?*?<p><b>Sample?usage:</b>?Here?is?a?pair?of?classes?in?which?a?group
?*?of?worker?threads?use?two?countdown?latches:
?*?<ul>
?*?<li>The?first?is?a?start?signal?that?prevents?any?worker?from?proceeding
?*?until?the?driver?is?ready?for?them?to?proceed;
?*?<li>The?second?is?a?completion?signal?that?allows?the?driver?to?wait
?*?until?all?workers?have?completed.
?*?</ul>
?*
?*??<pre>?{@code
?*?class?Driver?{?//?...
?*???void?main()?throws?InterruptedException?{
?*?????CountDownLatch?startSignal?=?new?CountDownLatch(1);
?*?????CountDownLatch?doneSignal?=?new?CountDownLatch(N);
?*
?*?????for?(int?i?=?0;?i?<?N;?++i)?//?create?and?start?threads
?*???????new?Thread(new?Worker(startSignal,?doneSignal)).start();
?*
?*?????doSomethingElse();????????????//?don't?let?run?yet
?*?????startSignal.countDown();??????//?let?all?threads?proceed
?*?????doSomethingElse();
?*?????doneSignal.await();???????????//?wait?for?all?to?finish
?*???}
?*?}
?*
?*?class?Worker?implements?Runnable?{
?*???private?final?CountDownLatch?startSignal;
?*???private?final?CountDownLatch?doneSignal;
?*???Worker(CountDownLatch?startSignal,?CountDownLatch?doneSignal)?{
?*?????this.startSignal?=?startSignal;
?*?????this.doneSignal?=?doneSignal;
?*???}
?*???public?void?run()?{
?*?????try?{
?*???????startSignal.await();
?*???????doWork();
?*???????doneSignal.countDown();
?*?????}?catch?(InterruptedException?ex)?{}?//?return;
?*???}
?*
?*???void?doWork()?{?...?}
?*?}}</pre>
?*
?*?<p>Another?typical?usage?would?be?to?divide?a?problem?into?N?parts,
?*?describe?each?part?with?a?Runnable?that?executes?that?portion?and
?*?counts?down?on?the?latch,?and?queue?all?the?Runnables?to?an
?*?Executor.??When?all?sub-parts?are?complete,?the?coordinating?thread
?*?will?be?able?to?pass?through?await.?(When?threads?must?repeatedly
?*?count?down?in?this?way,?instead?use?a?{@link?CyclicBarrier}.)
?*
?*??<pre>?{@code
?*?class?Driver2?{?//?...
?*???void?main()?throws?InterruptedException?{
?*?????CountDownLatch?doneSignal?=?new?CountDownLatch(N);
?*?????Executor?e?=?...
?*
?*?????for?(int?i?=?0;?i?<?N;?++i)?//?create?and?start?threads
?*???????e.execute(new?WorkerRunnable(doneSignal,?i));
?*
?*?????doneSignal.await();???????????//?wait?for?all?to?finish
?*???}
?*?}
?*
?*?class?WorkerRunnable?implements?Runnable?{
?*???private?final?CountDownLatch?doneSignal;
?*???private?final?int?i;
?*???WorkerRunnable(CountDownLatch?doneSignal,?int?i)?{
?*?????this.doneSignal?=?doneSignal;
?*?????this.i?=?i;
?*???}
?*???public?void?run()?{
?*?????try?{
?*???????doWork(i);
?*???????doneSignal.countDown();
?*?????}?catch?(InterruptedException?ex)?{}?//?return;
?*???}
?*
?*???void?doWork()?{?...?}
?*?}}</pre>
?*
?*?<p>Memory?consistency?effects:?Until?the?count?reaches
?*?zero,?actions?in?a?thread?prior?to?calling
?*?{@code?countDown()}
?*?<a?href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
?*?actions?following?a?successful?return?from?a?corresponding
?*?{@code?await()}?in?another?thread.
?*
?*?@since?1.5
?*?@author?Doug?Lea
?*/
public?class?CountDownLatch?{
????/**
?*?CountDownLatch??内部类
?????*?Synchronization?control?For?CountDownLatch.
?*倒计时锁存器的同步控制。
?????*?Uses?AQS?state?to?represent?count.
?*采用AQS状来代表计数的。
?????*/
????private?static?final?class?Sync?extends?AbstractQueuedSynchronizer?{
????????private?static?final?long?serialVersionUID?=?4982264981922014374L;
????????Sync(int?count)?{
????????????setState(count);
????????}
????????int?getCount()?{
????????????return?getState();
????????}
????????protected?int?tryAcquireShared(int?acquires)?{
????????????return?(getState()?==?0)???1?:?-1;
????????}
????????protected?boolean?tryReleaseShared(int?releases)?{
????????????//?Decrement?count;?signal?when?transition?to?zero
//操作递减计数；转换为零时的信号
????????????for?(;;)?{
????????????????int?c?=?getState();
????????????????if?(c?==?0)
????????????????????return?false;
????????????????int?nextc?=?c-1;
????????????????if?(compareAndSetState(c,?nextc))
????????????????????return?nextc?==?0;
????????????}
????????}
????}
????private?final?Sync?sync;
????/**
?????*?Constructs?a?{@code?CountDownLatch}?initialized?with?the?given?count.
?????*基于给定的count来初始化CountDownLatch对象
?????*?@param?count?the?number?of?times?{@link?#countDown}?must?be?invoked
?????*????????before?threads?can?pass?through?{@link?#await}
?*?参数说明：在调用await之前需要调用的次数
?????*?@throws?IllegalArgumentException?if?{@code?count}?is?negative
?????*/
????public?CountDownLatch(int?count)?{
????????if?(count?<?0)?throw?new?IllegalArgumentException("count?<?0");
????????this.sync?=?new?Sync(count);
????}
????/**
?????*?Causes?the?current?thread?to?wait?until?the?latch?has?counted?down?to
?????*?zero,?unless?the?thread?is?{@linkplain?Thread#interrupt?interrupted}.
?????*
?????*?<p>If?the?current?count?is?zero?then?this?method?returns?immediately.
?????*
?????*?<p>If?the?current?count?is?greater?than?zero?then?the?current
?????*?thread?becomes?disabled?for?thread?scheduling?purposes?and?lies
?????*?dormant?until?one?of?two?things?happen:
?????*?<ul>
?????*?<li>The?count?reaches?zero?due?to?invocations?of?the
?????*?{@link?#countDown}?method;?or
?????*?<li>Some?other?thread?{@linkplain?Thread#interrupt?interrupts}
?????*?the?current?thread.
?????*?</ul>
?????*
?????*?<p>If?the?current?thread:
?????*?<ul>
?????*?<li>has?its?interrupted?status?set?on?entry?to?this?method;?or
?????*?<li>is?{@linkplain?Thread#interrupt?interrupted}?while?waiting,
?????*?</ul>
?????*?then?{@link?InterruptedException}?is?thrown?and?the?current?thread's
?????*?interrupted?status?is?cleared.
?????*
?????*?@throws?InterruptedException?if?the?current?thread?is?interrupted
?????*?????????while?waiting
?????*/
????public?void?await()?throws?InterruptedException?{
????????sync.acquireSharedInterruptibly(1);
????}
????/**
?*?是否可以唤起其他线程方法
?????*?Causes?the?current?thread?to?wait?until?the?latch?has?counted?down?to
?????*?zero,?unless?the?thread?is?{@linkplain?Thread#interrupt?interrupted},
?????*?or?the?specified?waiting?time?elapses.
?*使当前线程等待，直到计时器已倒计时为零，除非线程抛出interrupted异常或者指定的等待时间已过。
?????*
?????*?<p>If?the?current?count?is?zero?then?this?method?returns?immediately
?????*?with?the?value?{@code?true}.
?*?如果当前计数器count是零的话，这个方法立马返回ture
?????*
?????*?<p>If?the?current?count?is?greater?than?zero?then?the?current
?????*?thread?becomes?disabled?for?thread?scheduling?purposes?and?lies
?????*?dormant?until?one?of?three?things?happen:
?*如果当前计数大于零，则当前由于线程调度的目的，线程被禁用，并且存在在以下三种情况发生之前休眠：
?????*?<ul>
?????*?<li>The?count?reaches?zero?due?to?invocations?of?the
?????*?{@link?#countDown}?method;?or
?????*?<li>Some?other?thread?{@linkplain?Thread#interrupt?interrupts}
?????*?the?current?thread;?or
?????*?<li>The?specified?waiting?time?elapses.
?*?1：由于调用了countDown方法是的count的值为零;
?*?2：或由于当前线程中其他线程抛出了?interrupts异常(中断异常);
?*?3：或指定的等待时间已过。
?????*?</ul>
?????*
?????*?<p>If?the?count?reaches?zero?then?the?method?returns?with?the
?????*?value?{@code?true}.
?*?如果计数为零，则方法返回值
?????*
?????*?<p>If?the?current?thread:
?????*?<ul>
?????*?<li>has?its?interrupted?status?set?on?entry?to?this?method;?or
?????*?<li>is?{@linkplain?Thread#interrupt?interrupted}?while?waiting,
?????*?</ul>
?????*?then?{@link?InterruptedException}?is?thrown?and?the?current?thread's
?????*?interrupted?status?is?cleared.
?*?如果当前线程出现以下情况，当前线程中断的状态将会被清除掉
?*?1：在调用await此方法的时候，线程被标记为中断状态的;
?*?2：或者在等待的过程中抛出了中断异常的时候。
?????*
?????*?<p>If?the?specified?waiting?time?elapses?then?the?value?{@code?false}
?????*?is?returned.??If?the?time?is?less?than?or?equal?to?zero,?the?method
?????*?will?not?wait?at?all.
?*?如果设置等待的时间超时，返回false.
?*?如果运行次数小于或者是等于0，这个方法就不会再等待了
?????*
?????*?@param?timeout?the?maximum?time?to?wait：超时等待的最长时间
?????*?@param?unit?the?time?unit?of?the?{@code?timeout}?argument?超时等待时间单位
?????*?@return?{@code?true}?if?the?count?reached?zero?and?{@code?false}
?????*?????????if?the?waiting?time?elapsed?before?the?count?reached?zero
?????*?@throws?InterruptedException?if?the?current?thread?is?interrupted
?????*?????????while?waiting
?????*/
????public?boolean?await(long?timeout,?TimeUnit?unit)
????????throws?InterruptedException?{
????????return?sync.tryAcquireSharedNanos(1,?unit.toNanos(timeout));
????}
????/**
?*?计数器减少1的方法。
?????*?Decrements?the?count?of?the?latch,?releasing?all?waiting?threads?if
?????*?the?count?reaches?zero.
?????*?计数器减少1的方法，如果计数达到零，则释放所有等待的线程。
?????*?<p>If?the?current?count?is?greater?than?zero?then?it?is?decremented.
?*如果当前计数大于零，则将其递减。
?????*?If?the?new?count?is?zero?then?all?waiting?threads?are?re-enabled?for
?????*?thread?scheduling?purposes.
?*?如果新计数为零，则所有等待的线程都将重新启用以进行线程调度。
?????*
?????*?<p>If?the?current?count?equals?zero?then?nothing?happens.
?*如果当前计数等于零，则不会发生任何事情。
?????*/
????public?void?countDown()?{
????????sync.releaseShared(1);
????}
????/**
?????*?Returns?the?current?count.
?????*
?????*?<p>This?method?is?typically?used?for?debugging?and?testing?purposes.
?????*
?????*?@return?the?current?count
?????*/
????public?long?getCount()?{
????????return?sync.getCount();
????}
????/**
?????*?Returns?a?string?identifying?this?latch,?as?well?as?its?state.
?????*?The?state,?in?brackets,?includes?the?String?{@code?"Count?="}
?????*?followed?by?the?current?count.
?????*
?????*?@return?a?string?identifying?this?latch,?as?well?as?its?state
?????*/
????public?String?toString()?{
????????return?super.toString()?+?"[Count?=?"?+?sync.getCount()?+?"]";
????}
}本文参与?腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。
原始发表：2020-03-17 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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