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中很重要的一块内容,可以先看段示例代码,这段代码应该来自于Doug Lea大大,可以在 javadoc 中的 condition 部分找到,其实大大原来写过基于 synchronized 实现的,后面我也贴下代码" itemprop=description></span><header class=post-header><h1 itemprop="name headline" class=post-title>AQS篇二 之 Condition 浅析笔记</h1><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间:2021-02-21 21:27:06" datetime=2021-02-21T21:27:06+08:00>2021-02-21</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/%E5%B9%B6%E5%8F%91/ itemprop=url rel=index><span itemprop=name>并发</span></a> </span></span><span class="post-meta-item cloudflare-page-counter" data-title="AQS篇二 之 Condition 浅析笔记" data-increment=true data-path=/2021/02/21/AQS-%E4%B9%8B-Condition-%E6%B5%85%E6%9E%90%E7%AC%94%E8%AE%B0/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数:</span> <span class=cloudflare-page-counter-count></span></span></div><div class=post-description>Condition也是 AQS 中很重要的一块内容,可以先看段示例代码,这段代码应该来自于Doug Lea大大,可以在 javadoc 中的 condition 部分找到,其实大大原来写过基于 synchronized 实现的,后面我也贴下代码</div></div></header><div class=post-body itemprop=articleBody><p>Condition也是 AQS 中很重要的一块内容,可以先看段示例代码,这段代码应该来自于Doug Lea大大,可以在 javadoc 中的 <a href=https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/Condition.html rel=noopener target=_blank>condition</a> 部分找到,其实大大原来写过基于 <code>synchronized</code> 实现的,后面我也贴下代码<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br></pre><td class=code><pre><span class=line><span class=keyword>import</span> java.util.concurrent.locks.Condition;</span><br><span class=line><span class=keyword>import</span> java.util.concurrent.locks.Lock;</span><br><span class=line><span class=keyword>import</span> java.util.concurrent.locks.ReentrantLock;</span><br><span class=line></span><br><span class=line><span class=keyword>class</span> <span class="title class_">BoundedBuffer</span> {</span><br><span class=line> <span class=keyword>final</span> <span class=type>Lock</span> <span class=variable>lock</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">ReentrantLock</span>();</span><br><span class=line> <span class=comment>// condition 依赖于 lock 来产生</span></span><br><span class=line> <span class=keyword>final</span> <span class=type>Condition</span> <span class=variable>notFull</span> <span class=operator>=</span> lock.newCondition();</span><br><span class=line> <span class=keyword>final</span> <span class=type>Condition</span> <span class=variable>notEmpty</span> <span class=operator>=</span> lock.newCondition();</span><br><span class=line></span><br><span class=line> <span class=comment>// 对象池子,put 跟 take 的就是这里的</span></span><br><span class=line> <span class=keyword>final</span> Object[] items = <span class=keyword>new</span> <span class="title class_">Object</span>[<span class=number>100</span>];</span><br><span class=line> <span class=type>int</span> putptr, takeptr, count;</span><br><span class=line></span><br><span class=line> <span class=comment>// 生产</span></span><br><span class=line> <span class=keyword>public</span> <span class=keyword>void</span> <span class="title function_">put</span><span class=params>(Object x)</span> <span class=keyword>throws</span> InterruptedException {</span><br><span class=line> <span class=comment>// 这里也说明了,需要先拥有锁</span></span><br><span class=line> lock.lock();</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=keyword>while</span> (count == items.length)</span><br><span class=line> notFull.await(); <span class=comment>// 队列已满,等待,直到 not full 才能继续生产</span></span><br><span class=line> items[putptr] = x;</span><br><span class=line> <span class=keyword>if</span> (++putptr == items.length) putptr = <span class=number>0</span>;</span><br><span class=line> ++count;</span><br><span class=line> notEmpty.signal(); <span class=comment>// 生产成功,队列已经 not empty 了,发个通知出去</span></span><br><span class=line> } <span class=keyword>finally</span> {</span><br><span class=line> lock.unlock();</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// 消费</span></span><br><span class=line> <span class=keyword>public</span> Object <span class="title function_">take</span><span class=params>()</span> <span class=keyword>throws</span> InterruptedException {</span><br><span class=line> lock.lock();</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=keyword>while</span> (count == <span class=number>0</span>)</span><br><span class=line> notEmpty.await(); <span class=comment>// 队列为空,等待,直到队列 not empty,才能继续消费</span></span><br><span class=line> <span class=type>Object</span> <span class=variable>x</span> <span class=operator>=</span> items[takeptr];</span><br><span class=line> <span class=keyword>if</span> (++takeptr == items.length) takeptr = <span class=number>0</span>;</span><br><span class=line> --count;</span><br><span class=line> notFull.signal(); <span class=comment>// 被我消费掉一个,队列 not full 了,发个通知出去</span></span><br><span class=line> <span class=keyword>return</span> x;</span><br><span class=line> } <span class=keyword>finally</span> {</span><br><span class=line> lock.unlock();</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>介绍下 Condition 的结构<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <span class=keyword>class</span> <span class="title class_">ConditionObject</span> <span class=keyword>implements</span> <span class="title class_">Condition</span>, java.io.Serializable {</span><br><span class=line> <span class=keyword>private</span> <span class=keyword>static</span> <span class=keyword>final</span> <span class=type>long</span> <span class=variable>serialVersionUID</span> <span class=operator>=</span> <span class=number>1173984872572414699L</span>;</span><br><span class=line> <span class=comment>/** First node of condition queue. */</span></span><br><span class=line> <span class=keyword>private</span> <span class=keyword>transient</span> Node firstWaiter;</span><br><span class=line> <span class=comment>/** Last node of condition queue. */</span></span><br><span class=line> <span class=keyword>private</span> <span class=keyword>transient</span> Node lastWaiter;</span><br></pre></table></figure><p>主要的就这么点,而且也复用了 AQS 阻塞队列或者大大叫 <code>lock queue</code>中同样的 Node 节点,只不过它没有使用其中的双向队列,也就是prev 和 next,而是在 Node 中的 nextWaiter,所以只是个单向的队列,没使用 next 其实还有个用处,后面会提到,看下结构的示意图<br><img loading=lazy src=https://img.nicksxs.me/uPic/Ss9oFX.png><br>然后主要是看两个方法,<code>await</code> 和 <code>signal</code>,<br>先来看下 await<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Implements interruptible condition wait.</span></span><br><span class=line><span class=comment> * &LTol></span></span><br><span class=line><span class=comment> * &LTli> If current thread is interrupted, throw InterruptedException.</span></span><br><span class=line><span class=comment> * &LTli> Save lock state returned by {<span class=doctag>@link</span> #getState}.</span></span><br><span class=line><span class=comment> * &LTli> Invoke {<span class=doctag>@link</span> #release} with saved state as argument,</span></span><br><span class=line><span class=comment> * throwing IllegalMonitorStateException if it fails.</span></span><br><span class=line><span class=comment> * &LTli> Block until signalled or interrupted.</span></span><br><span class=line><span class=comment> * &LTli> Reacquire by invoking specialized version of</span></span><br><span class=line><span class=comment> * {<span class=doctag>@link</span> #acquire} with saved state as argument.</span></span><br><span class=line><span class=comment> * &LTli> If interrupted while blocked in step 4, throw InterruptedException.</span></span><br><span class=line><span class=comment> * &LT/ol></span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>public</span> <span class=keyword>final</span> <span class=keyword>void</span> <span class="title function_">await</span><span class=params>()</span> <span class=keyword>throws</span> InterruptedException {</span><br><span class=line> <span class=keyword>if</span> (Thread.interrupted())</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">InterruptedException</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// 将当前节点包装成一个 condition waiter node 节点</span></span><br><span class=line> <span class=type>Node</span> <span class=variable>node</span> <span class=operator>=</span> addConditionWaiter();</span><br><span class=line></span><br><span class=line> <span class=comment>// 完全释放占有的锁,这里需要是占有锁的线程</span></span><br><span class=line> <span class=type>int</span> <span class=variable>savedState</span> <span class=operator>=</span> fullyRelease(node);</span><br><span class=line> <span class=type>int</span> <span class=variable>interruptMode</span> <span class=operator>=</span> <span class=number>0</span>;</span><br><span class=line></span><br><span class=line> <span class=comment>// 判断下是否在阻塞队列中,因为有可能被其他节点从等待队列移动到阻塞队列</span></span><br><span class=line> <span class=keyword>while</span> (!isOnSyncQueue(node)) {</span><br><span class=line> <span class=comment>// park等待,等待被唤醒</span></span><br><span class=line> LockSupport.park(<span class=built_in>this</span>);</span><br><span class=line> <span class=keyword>if</span> ((interruptMode = checkInterruptWhileWaiting(node)) != <span class=number>0</span>)</span><br><span class=line> <span class=keyword>break</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// 被唤醒后进入阻塞队列,等待获取锁,这里继续用了fullyRelease返回的 state</span></span><br><span class=line> <span class=keyword>if</span> (acquireQueued(node, savedState) && interruptMode != THROW_IE)</span><br><span class=line> interruptMode = REINTERRUPT;</span><br><span class=line> <span class=keyword>if</span> (node.nextWaiter != <span class=literal>null</span>) <span class=comment>// clean up if cancelled</span></span><br><span class=line> unlinkCancelledWaiters();</span><br><span class=line> <span class=keyword>if</span> (interruptMode != <span class=number>0</span>)</span><br><span class=line> reportInterruptAfterWait(interruptMode);</span><br><span class=line>}</span><br></pre></table></figure><p>添加条件队列节点<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Adds a new waiter to wait queue.</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> its new wait node</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>private</span> Node <span class="title function_">addConditionWaiter</span><span class=params>()</span> {</span><br><span class=line> <span class=type>Node</span> <span class=variable>t</span> <span class=operator>=</span> lastWaiter;</span><br><span class=line> <span class=comment>// If lastWaiter is cancelled, clean out.</span></span><br><span class=line> <span class=comment>// 如果节点已经不是 CONDITION 状态了,表示已经取消了</span></span><br><span class=line> <span class=keyword>if</span> (t != <span class=literal>null</span> && t.waitStatus != Node.CONDITION) {</span><br><span class=line> <span class=comment>// 把等待队列中取消的节点清理出去</span></span><br><span class=line> unlinkCancelledWaiters();</span><br><span class=line> t = lastWaiter;</span><br><span class=line> }</span><br><span class=line> <span class=comment>// 把当前线程包装成waitStatus=CONDITION 的节点</span></span><br><span class=line> <span class=type>Node</span> <span class=variable>node</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">Node</span>(Thread.currentThread(), Node.CONDITION);</span><br><span class=line> <span class=comment>// 没有 lastWaiter 节点,直接是 firstWaiter</span></span><br><span class=line> <span class=keyword>if</span> (t == <span class=literal>null</span>)</span><br><span class=line> firstWaiter = node;</span><br><span class=line> <span class=keyword>else</span></span><br><span class=line> <span class=comment>// 不然就接在 lastWaiter 后面</span></span><br><span class=line> t.nextWaiter = node;</span><br><span class=line> <span class=comment>// 当前节点就会变成新的 lastWaiter</span></span><br><span class=line> lastWaiter = node;</span><br><span class=line> <span class=keyword>return</span> node;</span><br><span class=line>}</span><br></pre></table></figure><p>清理取消的节点<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Unlinks cancelled waiter nodes from condition queue.</span></span><br><span class=line><span class=comment> * Called only while holding lock. This is called when</span></span><br><span class=line><span class=comment> * cancellation occurred during condition wait, and upon</span></span><br><span class=line><span class=comment> * insertion of a new waiter when lastWaiter is seen to have</span></span><br><span class=line><span class=comment> * been cancelled. This method is needed to avoid garbage</span></span><br><span class=line><span class=comment> * retention in the absence of signals. So even though it may</span></span><br><span class=line><span class=comment> * require a full traversal, it comes into play only when</span></span><br><span class=line><span class=comment> * timeouts or cancellations occur in the absence of</span></span><br><span class=line><span class=comment> * signals. It traverses all nodes rather than stopping at a</span></span><br><span class=line><span class=comment> * particular target to unlink all pointers to garbage nodes</span></span><br><span class=line><span class=comment> * without requiring many re-traversals during cancellation</span></span><br><span class=line><span class=comment> * storms.</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">unlinkCancelledWaiters</span><span class=params>()</span> {</span><br><span class=line> <span class=type>Node</span> <span class=variable>t</span> <span class=operator>=</span> firstWaiter;</span><br><span class=line> <span class=type>Node</span> <span class=variable>trail</span> <span class=operator>=</span> <span class=literal>null</span>;</span><br><span class=line> <span class=comment>// 循环遍历单向链表的节点,如果状态不是 CONDITION 就清出去</span></span><br><span class=line> <span class=keyword>while</span> (t != <span class=literal>null</span>) {</span><br><span class=line> <span class=type>Node</span> <span class=variable>next</span> <span class=operator>=</span> t.nextWaiter;</span><br><span class=line> <span class=comment>// 循环链表操作,清掉取消的节点</span></span><br><span class=line> <span class=keyword>if</span> (t.waitStatus != Node.CONDITION) {</span><br><span class=line> t.nextWaiter = <span class=literal>null</span>;</span><br><span class=line> <span class=keyword>if</span> (trail == <span class=literal>null</span>)</span><br><span class=line> firstWaiter = next;</span><br><span class=line> <span class=keyword>else</span></span><br><span class=line> trail.nextWaiter = next;</span><br><span class=line> <span class=keyword>if</span> (next == <span class=literal>null</span>)</span><br><span class=line> lastWaiter = trail;</span><br><span class=line> }</span><br><span class=line> <span class=keyword>else</span></span><br><span class=line> trail = t;</span><br><span class=line> t = next;</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>完全释放锁<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Invokes release with current state value; returns saved state.</span></span><br><span class=line><span class=comment> * Cancels node and throws exception on failure.</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> node the condition node for this wait</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> previous sync state</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>final</span> <span class=type>int</span> <span class="title function_">fullyRelease</span><span class=params>(Node node)</span> {</span><br><span class=line> <span class=type>boolean</span> <span class=variable>failed</span> <span class=operator>=</span> <span class=literal>true</span>;</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=comment>// 获取下当前的 state 值,因为是可重入的,所以这个值要保存下来</span></span><br><span class=line> <span class=type>int</span> <span class=variable>savedState</span> <span class=operator>=</span> getState();</span><br><span class=line> <span class=comment>// 这里还包含比较多操作,不过跟前面分析 AQS 的释放比较类似,不深入了</span></span><br><span class=line> <span class=keyword>if</span> (release(savedState)) {</span><br><span class=line> failed = <span class=literal>false</span>;</span><br><span class=line> <span class=comment>// 返回这个值</span></span><br><span class=line> <span class=keyword>return</span> savedState;</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">IllegalMonitorStateException</span>();</span><br><span class=line> }</span><br><span class=line> } <span class=keyword>finally</span> {</span><br><span class=line> <span class=keyword>if</span> (failed)</span><br><span class=line> node.waitStatus = Node.CANCELLED;</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>判断是否在阻塞队列中<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Returns true if a node, always one that was initially placed on</span></span><br><span class=line><span class=comment> * a condition queue, is now waiting to reacquire on sync queue.</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> node the node</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> true if is reacquiring</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>final</span> <span class=type>boolean</span> <span class="title function_">isOnSyncQueue</span><span class=params>(Node node)</span> {</span><br><span class=line> <span class=comment>// 如果waitStatus 是 CONDITION 或者没有 prev 前置节点肯定就不在</span></span><br><span class=line> <span class=keyword>if</span> (node.waitStatus == Node.CONDITION || node.prev == <span class=literal>null</span>)</span><br><span class=line> <span class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> <span class=comment>// 这里就是我前面提到的 next 的作用</span></span><br><span class=line> <span class=keyword>if</span> (node.next != <span class=literal>null</span>) <span class=comment>// If has successor, it must be on queue</span></span><br><span class=line> <span class=keyword>return</span> <span class=literal>true</span>;</span><br><span class=line> <span class=comment>// 从 tail 开始找,是否在阻塞队列中</span></span><br><span class=line> <span class=comment>/*</span></span><br><span class=line><span class=comment> * node.prev can be non-null, but not yet on queue because</span></span><br><span class=line><span class=comment> * the CAS to place it on queue can fail. So we have to</span></span><br><span class=line><span class=comment> * traverse from tail to make sure it actually made it. It</span></span><br><span class=line><span class=comment> * will always be near the tail in calls to this method, and</span></span><br><span class=line><span class=comment> * unless the CAS failed (which is unlikely), it will be</span></span><br><span class=line><span class=comment> * there, so we hardly ever traverse much.</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line> <span class=keyword>return</span> findNodeFromTail(node);</span><br><span class=line>}</span><br><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Returns true if node is on sync queue by searching backwards from tail.</span></span><br><span class=line><span class=comment> * Called only when needed by isOnSyncQueue.</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> true if present</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>private</span> <span class=type>boolean</span> <span class="title function_">findNodeFromTail</span><span class=params>(Node node)</span> {</span><br><span class=line> <span class=type>Node</span> <span class=variable>t</span> <span class=operator>=</span> tail;</span><br><span class=line> <span class=comment>// 从 tail 开始,从后往前找</span></span><br><span class=line> <span class=keyword>for</span> (;;) {</span><br><span class=line> <span class=keyword>if</span> (t == node)</span><br><span class=line> <span class=keyword>return</span> <span class=literal>true</span>;</span><br><span class=line> <span class=keyword>if</span> (t == <span class=literal>null</span>)</span><br><span class=line> <span class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> t = t.prev;</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>await 的逻辑差不多就是这样子,主要的就是把自己包成一个 Node 节点,waitStatus 的状态是 CONDITION,挂在等待队列的最后,然后完全释放锁,park 等待<h2 id=signal><a class=headerlink href=#signal title=signal></a>signal</h2><figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Moves the longest-waiting thread, if one exists, from the</span></span><br><span class=line><span class=comment> * wait queue for this condition to the wait queue for the</span></span><br><span class=line><span class=comment> * owning lock.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * <span class=doctag>@throws</span> IllegalMonitorStateException if {<span class=doctag>@link</span> #isHeldExclusively}</span></span><br><span class=line><span class=comment> * returns {<span class=doctag>@code</span> false}</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>public</span> <span class=keyword>final</span> <span class=keyword>void</span> <span class="title function_">signal</span><span class=params>()</span> {</span><br><span class=line> <span class=keyword>if</span> (!isHeldExclusively())</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">IllegalMonitorStateException</span>();</span><br><span class=line> <span class=comment>// firstWaiter 肯定是最早开始等待的</span></span><br><span class=line> <span class=type>Node</span> <span class=variable>first</span> <span class=operator>=</span> firstWaiter;</span><br><span class=line> <span class=comment>// 如果不为空就唤醒</span></span><br><span class=line> <span class=keyword>if</span> (first != <span class=literal>null</span>)</span><br><span class=line> doSignal(first);</span><br><span class=line>}</span><br><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Removes and transfers nodes until hit non-cancelled one or</span></span><br><span class=line><span class=comment> * null. Split out from signal in part to encourage compilers</span></span><br><span class=line><span class=comment> * to inline the case of no waiters.</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> first (non-null) the first node on condition queue</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">doSignal</span><span class=params>(Node first)</span> {</span><br><span class=line> <span class=keyword>do</span> {</span><br><span class=line> <span class=comment>// 因为要去唤醒 first 节点了,firstWaiter 需要再从后面找一个</span></span><br><span class=line> <span class=comment>// 并且判断是否为空,如果是空的话就直接可以把 lastWaiter 设置成空了</span></span><br><span class=line> <span class=keyword>if</span> ( (firstWaiter = first.nextWaiter) == <span class=literal>null</span>)</span><br><span class=line> lastWaiter = <span class=literal>null</span>;</span><br><span class=line> <span class=comment>// first 不需要继续保存后面的 waiter 了,因为 firstWaiter 已经是 first 的后置节点了</span></span><br><span class=line> first.nextWaiter = <span class=literal>null</span>;</span><br><span class=line> <span class=comment>// 如果 first 节点转移不成功,并且 firstWaiter 节点不为空,则继续进入循环</span></span><br><span class=line> } <span class=keyword>while</span> (!transferForSignal(first) &&</span><br><span class=line> (first = firstWaiter) != <span class=literal>null</span>);</span><br><span class=line>}</span><br><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Transfers a node from a condition queue onto sync queue.</span></span><br><span class=line><span class=comment> * Returns true if successful.</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> node the node</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> true if successfully transferred (else the node was</span></span><br><span class=line><span class=comment> * cancelled before signal)</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line><span class=keyword>final</span> <span class=type>boolean</span> <span class="title function_">transferForSignal</span><span class=params>(Node node)</span> {</span><br><span class=line> <span class=comment>/*</span></span><br><span class=line><span class=comment> * If cannot change waitStatus, the node has been cancelled.</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line> <span class=comment>// 如果状态已经不是 CONDITION 就不会设置成功,返回 false</span></span><br><span class=line> <span class=keyword>if</span> (!compareAndSetWaitStatus(node, Node.CONDITION, <span class=number>0</span>))</span><br><span class=line> <span class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> <span class=comment>/*</span></span><br><span class=line><span class=comment> * Splice onto queue and try to set waitStatus of predecessor to</span></span><br><span class=line><span class=comment> * indicate that thread is (probably) waiting. If cancelled or</span></span><br><span class=line><span class=comment> * attempt to set waitStatus fails, wake up to resync (in which</span></span><br><span class=line><span class=comment> * case the waitStatus can be transiently and harmlessly wrong).</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line> <span class=comment>// 调用跟aqs 第一篇中一样的 enq 方法进入阻塞队列,返回入队后的前一节点</span></span><br><span class=line> <span class=type>Node</span> <span class=variable>p</span> <span class=operator>=</span> enq(node);</span><br><span class=line> <span class=type>int</span> <span class=variable>ws</span> <span class=operator>=</span> p.waitStatus;</span><br><span class=line> <span class=comment>// 将前置节点状态设置成SIGNAL,表示后面有节点在等了</span></span><br><span class=line> <span class=keyword>if</span> (ws > <span class=number>0</span> || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))</span><br><span class=line> LockSupport.unpark(node.thread);</span><br><span class=line> <span class=comment>// 返回 true,上一个方法的循环就退出了</span></span><br><span class=line> <span class=keyword>return</span> <span class=literal>true</span>;</span><br><span class=line>}</span><br></pre></table></figure><p>这里其实就是把 condition 等待队列的第一个未取消的节点入队到阻塞队列去争锁<h2 id=附录><a class=headerlink href=#附录 title=附录></a>附录</h2><p><code>synchronized</code> 版的 BoundedBuffer<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br><span class=line>65</span><br><span class=line>66</span><br><span class=line>67</span><br><span class=line>68</span><br><span class=line>69</span><br><span class=line>70</span><br><span class=line>71</span><br><span class=line>72</span><br><span class=line>73</span><br><span class=line>74</span><br><span class=line>75</span><br><span class=line>76</span><br><span class=line>77</span><br><span class=line>78</span><br><span class=line>79</span><br><span class=line>80</span><br><span class=line>81</span><br><span class=line>82</span><br><span class=line>83</span><br><span class=line>84</span><br><span class=line>85</span><br><span class=line>86</span><br><span class=line>87</span><br><span class=line>88</span><br><span class=line>89</span><br><span class=line>90</span><br><span class=line>91</span><br><span class=line>92</span><br><span class=line>93</span><br><span class=line>94</span><br><span class=line>95</span><br><span class=line>96</span><br><span class=line>97</span><br><span class=line>98</span><br><span class=line>99</span><br><span class=line>100</span><br><span class=line>101</span><br><span class=line>102</span><br><span class=line>103</span><br><span class=line>104</span><br><span class=line>105</span><br><span class=line>106</span><br><span class=line>107</span><br><span class=line>108</span><br><span class=line>109</span><br><span class=line>110</span><br><span class=line>111</span><br><span class=line>112</span><br><span class=line>113</span><br><span class=line>114</span><br><span class=line>115</span><br><span class=line>116</span><br><span class=line>117</span><br><span class=line>118</span><br><span class=line>119</span><br><span class=line>120</span><br><span class=line>121</span><br><span class=line>122</span><br><span class=line>123</span><br><span class=line>124</span><br><span class=line>125</span><br><span class=line>126</span><br><span class=line>127</span><br><span class=line>128</span><br><span class=line>129</span><br><span class=line>130</span><br><span class=line>131</span><br><span class=line>132</span><br><span class=line>133</span><br><span class=line>134</span><br><span class=line>135</span><br><span class=line>136</span><br><span class=line>137</span><br><span class=line>138</span><br><span class=line>139</span><br><span class=line>140</span><br><span class=line>141</span><br><span class=line>142</span><br><span class=line>143</span><br><span class=line>144</span><br><span class=line>145</span><br><span class=line>146</span><br><span class=line>147</span><br><span class=line>148</span><br><span class=line>149</span><br><span class=line>150</span><br><span class=line>151</span><br><span class=line>152</span><br><span class=line>153</span><br><span class=line>154</span><br><span class=line>155</span><br><span class=line>156</span><br><span class=line>157</span><br><span class=line>158</span><br><span class=line>159</span><br><span class=line>160</span><br><span class=line>161</span><br><span class=line>162</span><br><span class=line>163</span><br><span class=line>164</span><br><span class=line>165</span><br><span class=line>166</span><br><span class=line>167</span><br><span class=line>168</span><br><span class=line>169</span><br><span class=line>170</span><br><span class=line>171</span><br><span class=line>172</span><br><span class=line>173</span><br><span class=line>174</span><br><span class=line>175</span><br><span class=line>176</span><br><span class=line>177</span><br><span class=line>178</span><br><span class=line>179</span><br><span class=line>180</span><br><span class=line>181</span><br><span class=line>182</span><br><span class=line>183</span><br><span class=line>184</span><br><span class=line>185</span><br></pre><td class=code><pre><span class=line><span class=comment>/*</span></span><br><span class=line><span class=comment> File: BoundedBuffer.java</span></span><br><span class=line><span class=comment></span></span><br><span class=line><span class=comment> Originally written by Doug Lea and released into the public domain.</span></span><br><span class=line><span class=comment> This may be used for any purposes whatsoever without acknowledgment.</span></span><br><span class=line><span class=comment> Thanks for the assistance and support of Sun Microsystems Labs,</span></span><br><span class=line><span class=comment> and everyone contributing, testing, and using this code.</span></span><br><span class=line><span class=comment></span></span><br><span class=line><span class=comment> History:</span></span><br><span class=line><span class=comment> Date Who What</span></span><br><span class=line><span class=comment> 11Jun1998 dl Create public version</span></span><br><span class=line><span class=comment> 17Jul1998 dl Simplified by eliminating wait counts</span></span><br><span class=line><span class=comment> 25aug1998 dl added peek</span></span><br><span class=line><span class=comment> 5May1999 dl replace % with conditional (slightly faster)</span></span><br><span class=line><span class=comment>*/</span></span><br><span class=line></span><br><span class=line><span class=keyword>package</span> EDU.oswego.cs.dl.util.concurrent;</span><br><span class=line></span><br><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Efficient array-based bounded buffer class.</span></span><br><span class=line><span class=comment> * Adapted from CPJ, chapter 8, which describes design.</span></span><br><span class=line><span class=comment> * &LTp>[&LTa href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. &LT/a>] &LTp></span></span><br><span class=line><span class=comment> **/</span></span><br><span class=line></span><br><span class=line><span class=keyword>public</span> <span class=keyword>class</span> <span class="title class_">BoundedBuffer</span> <span class=keyword>implements</span> <span class="title class_">BoundedChannel</span> {</span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>final</span> Object[] array_; <span class=comment>// the elements</span></span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=type>int</span> <span class=variable>takePtr_</span> <span class=operator>=</span> <span class=number>0</span>; <span class=comment>// circular indices</span></span><br><span class=line> <span class=keyword>protected</span> <span class=type>int</span> <span class=variable>putPtr_</span> <span class=operator>=</span> <span class=number>0</span>; </span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=type>int</span> <span class=variable>usedSlots_</span> <span class=operator>=</span> <span class=number>0</span>; <span class=comment>// length</span></span><br><span class=line> <span class=keyword>protected</span> <span class=type>int</span> emptySlots_; <span class=comment>// capacity - length</span></span><br><span class=line></span><br><span class=line> <span class=comment>/**</span></span><br><span class=line><span class=comment> * Helper monitor to handle puts. </span></span><br><span class=line><span class=comment> **/</span></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>final</span> <span class=type>Object</span> <span class=variable>putMonitor_</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">Object</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>/**</span></span><br><span class=line><span class=comment> * Create a BoundedBuffer with the given capacity.</span></span><br><span class=line><span class=comment> * <span class=doctag>@exception</span> IllegalArgumentException if capacity less or equal to zero</span></span><br><span class=line><span class=comment> **/</span></span><br><span class=line> <span class=keyword>public</span> <span class="title function_">BoundedBuffer</span><span class=params>(<span class=type>int</span> capacity)</span> <span class=keyword>throws</span> IllegalArgumentException {</span><br><span class=line> <span class=keyword>if</span> (capacity <= <span class=number>0</span>) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">IllegalArgumentException</span>();</span><br><span class=line> array_ = <span class=keyword>new</span> <span class="title class_">Object</span>[capacity];</span><br><span class=line> emptySlots_ = capacity;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/**</span></span><br><span class=line><span class=comment> * Create a buffer with the current default capacity</span></span><br><span class=line><span class=comment> **/</span></span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> <span class="title function_">BoundedBuffer</span><span class=params>()</span> { </span><br><span class=line> <span class=built_in>this</span>(DefaultChannelCapacity.get()); </span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>/** </span></span><br><span class=line><span class=comment> * Return the number of elements in the buffer.</span></span><br><span class=line><span class=comment> * This is only a snapshot value, that may change</span></span><br><span class=line><span class=comment> * immediately after returning.</span></span><br><span class=line><span class=comment> **/</span></span><br><span class=line> <span class=keyword>public</span> <span class=keyword>synchronized</span> <span class=type>int</span> <span class="title function_">size</span><span class=params>()</span> { <span class=keyword>return</span> usedSlots_; }</span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> <span class=type>int</span> <span class="title function_">capacity</span><span class=params>()</span> { <span class=keyword>return</span> array_.length; }</span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>void</span> <span class="title function_">incEmptySlots</span><span class=params>()</span> {</span><br><span class=line> <span class=keyword>synchronized</span>(putMonitor_) {</span><br><span class=line> ++emptySlots_;</span><br><span class=line> putMonitor_.notify();</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>synchronized</span> <span class=keyword>void</span> <span class="title function_">incUsedSlots</span><span class=params>()</span> {</span><br><span class=line> ++usedSlots_;</span><br><span class=line> notify();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>final</span> <span class=keyword>void</span> <span class="title function_">insert</span><span class=params>(Object x)</span> { <span class=comment>// mechanics of put</span></span><br><span class=line> --emptySlots_;</span><br><span class=line> array_[putPtr_] = x;</span><br><span class=line> <span class=keyword>if</span> (++putPtr_ >= array_.length) putPtr_ = <span class=number>0</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>final</span> Object <span class="title function_">extract</span><span class=params>()</span> { <span class=comment>// mechanics of take</span></span><br><span class=line> --usedSlots_;</span><br><span class=line> <span class=type>Object</span> <span class=variable>old</span> <span class=operator>=</span> array_[takePtr_];</span><br><span class=line> array_[takePtr_] = <span class=literal>null</span>;</span><br><span class=line> <span class=keyword>if</span> (++takePtr_ >= array_.length) takePtr_ = <span class=number>0</span>;</span><br><span class=line> <span class=keyword>return</span> old;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> Object <span class="title function_">peek</span><span class=params>()</span> {</span><br><span class=line> <span class=keyword>synchronized</span>(<span class=built_in>this</span>) {</span><br><span class=line> <span class=keyword>if</span> (usedSlots_ > <span class=number>0</span>)</span><br><span class=line> <span class=keyword>return</span> array_[takePtr_];</span><br><span class=line> <span class=keyword>else</span></span><br><span class=line> <span class=keyword>return</span> <span class=literal>null</span>;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> <span class=keyword>void</span> <span class="title function_">put</span><span class=params>(Object x)</span> <span class=keyword>throws</span> InterruptedException {</span><br><span class=line> <span class=keyword>if</span> (x == <span class=literal>null</span>) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">IllegalArgumentException</span>();</span><br><span class=line> <span class=keyword>if</span> (Thread.interrupted()) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">InterruptedException</span>();</span><br><span class=line></span><br><span class=line> <span class=keyword>synchronized</span>(putMonitor_) {</span><br><span class=line> <span class=keyword>while</span> (emptySlots_ <= <span class=number>0</span>) {</span><br><span class=line> <span class=keyword>try</span> { putMonitor_.wait(); }</span><br><span class=line> <span class=keyword>catch</span> (InterruptedException ex) {</span><br><span class=line> putMonitor_.notify();</span><br><span class=line> <span class=keyword>throw</span> ex;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> insert(x);</span><br><span class=line> }</span><br><span class=line> incUsedSlots();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> <span class=type>boolean</span> <span class="title function_">offer</span><span class=params>(Object x, <span class=type>long</span> msecs)</span> <span class=keyword>throws</span> InterruptedException {</span><br><span class=line> <span class=keyword>if</span> (x == <span class=literal>null</span>) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">IllegalArgumentException</span>();</span><br><span class=line> <span class=keyword>if</span> (Thread.interrupted()) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">InterruptedException</span>();</span><br><span class=line></span><br><span class=line> <span class=keyword>synchronized</span>(putMonitor_) {</span><br><span class=line> <span class=type>long</span> <span class=variable>start</span> <span class=operator>=</span> (msecs <= <span class=number>0</span>)? <span class=number>0</span> : System.currentTimeMillis();</span><br><span class=line> <span class=type>long</span> <span class=variable>waitTime</span> <span class=operator>=</span> msecs;</span><br><span class=line> <span class=keyword>while</span> (emptySlots_ <= <span class=number>0</span>) {</span><br><span class=line> <span class=keyword>if</span> (waitTime <= <span class=number>0</span>) <span class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> <span class=keyword>try</span> { putMonitor_.wait(waitTime); }</span><br><span class=line> <span class=keyword>catch</span> (InterruptedException ex) {</span><br><span class=line> putMonitor_.notify();</span><br><span class=line> <span class=keyword>throw</span> ex;</span><br><span class=line> }</span><br><span class=line> waitTime = msecs - (System.currentTimeMillis() - start);</span><br><span class=line> }</span><br><span class=line> insert(x);</span><br><span class=line> }</span><br><span class=line> incUsedSlots();</span><br><span class=line> <span class=keyword>return</span> <span class=literal>true</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line></span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> Object <span class="title function_">take</span><span class=params>()</span> <span class=keyword>throws</span> InterruptedException { </span><br><span class=line> <span class=keyword>if</span> (Thread.interrupted()) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">InterruptedException</span>();</span><br><span class=line> <span class=type>Object</span> <span class=variable>old</span> <span class=operator>=</span> <span class=literal>null</span>; </span><br><span class=line> <span class=keyword>synchronized</span>(<span class=built_in>this</span>) { </span><br><span class=line> <span class=keyword>while</span> (usedSlots_ <= <span class=number>0</span>) {</span><br><span class=line> <span class=keyword>try</span> { wait(); }</span><br><span class=line> <span class=keyword>catch</span> (InterruptedException ex) {</span><br><span class=line> notify();</span><br><span class=line> <span class=keyword>throw</span> ex; </span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> old = extract();</span><br><span class=line> }</span><br><span class=line> incEmptySlots();</span><br><span class=line> <span class=keyword>return</span> old;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> Object <span class="title function_">poll</span><span class=params>(<span class=type>long</span> msecs)</span> <span class=keyword>throws</span> InterruptedException { </span><br><span class=line> <span class=keyword>if</span> (Thread.interrupted()) <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">InterruptedException</span>();</span><br><span class=line> <span class=type>Object</span> <span class=variable>old</span> <span class=operator>=</span> <span class=literal>null</span>; </span><br><span class=line> <span class=keyword>synchronized</span>(<span class=built_in>this</span>) { </span><br><span class=line> <span class=type>long</span> <span class=variable>start</span> <span class=operator>=</span> (msecs <= <span class=number>0</span>)? <span class=number>0</span> : System.currentTimeMillis();</span><br><span class=line> <span class=type>long</span> <span class=variable>waitTime</span> <span class=operator>=</span> msecs;</span><br><span class=line> </span><br><span class=line> <span class=keyword>while</span> (usedSlots_ <= <span class=number>0</span>) {</span><br><span class=line> <span class=keyword>if</span> (waitTime <= <span class=number>0</span>) <span class=keyword>return</span> <span class=literal>null</span>;</span><br><span class=line> <span class=keyword>try</span> { wait(waitTime); }</span><br><span class=line> <span class=keyword>catch</span> (InterruptedException ex) {</span><br><span class=line> notify();</span><br><span class=line> <span class=keyword>throw</span> ex; </span><br><span class=line> }</span><br><span class=line> waitTime = msecs - (System.currentTimeMillis() - start);</span><br><span class=line></span><br><span class=line> }</span><br><span class=line> old = extract();</span><br><span class=line> }</span><br><span class=line> incEmptySlots();</span><br><span class=line> <span class=keyword>return</span> old;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line>}</span><br><span class=line></span><br></pre></table></figure></div><footer class=post-footer><div class="affiliate-creative affiliate-creative--post-end" data-affiliate-id=tencent-cloud-general><a rel="sponsored noopener" aria-label=腾讯云产品优惠 href=https://cloud.tencent.com/act/cps/redirect?redirect=2446&cps_key=2e33a1eedb380997d03618b4a5ba6ca7&from=console target=_blank><img alt=腾讯云服务器、数据库和云产品优惠 decoding=async height=419 loading=lazy src=/uploads/affiliate/tencent-cloud-general.webp width=690> </a><span 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