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itemprop=name><meta content="Nicksxs 的技术博客,深入 Java 运行时与生产诊断、低成本大模型推理和 Agent 工程实践。" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="AQS篇一 | Nicksxs's Blog" itemprop=name><meta content=很多东西都是时看时新,而且时间长了也会忘,所以再来复习下,也会有一些新的角度看法这次来聊下AQS的内容,主要是这几个点, itemprop=description></span><header class=post-header><h1 itemprop="name headline" class=post-title>AQS篇一</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:2021-02-14 22:51:54" datetime=2021-02-14T22:51:54+08:00>2021-02-14</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-increment=true data-path=/2021/02/14/AQS%E7%AF%87%E4%B8%80/ data-title=AQS篇一 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>很多东西都是时看时新,而且时间长了也会忘,所以再来复习下,也会有一些新的角度看法这次来聊下AQS的内容,主要是这几个点,</div></div></header><div class=post-body itemprop=articleBody><p>很多东西都是时看时新,而且时间长了也会忘,所以再来复习下,也会有一些新的角度看法这次来聊下AQS的内容,主要是这几个点,<h2 id=第一个线程><a class=headerlink href=#第一个线程 title=第一个线程></a>第一个线程</h2><p>第一个线程抢到锁了,此时state跟阻塞队列是怎么样的,其实这里是之前没理解对的地方<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></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Fair version of tryAcquire. Don't grant access unless</span></span><br><span class=line><span class=comment> * recursive call or no waiters or is first.</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>boolean</span> <span class="title function_">tryAcquire</span><span class=params>(<span class=type>int</span> acquires)</span> {</span><br><span class=line> <span class=keyword>final</span> <span class=type>Thread</span> <span class=variable>current</span> <span class=operator>=</span> Thread.currentThread();</span><br><span class=line> <span class=type>int</span> <span class=variable>c</span> <span class=operator>=</span> getState();</span><br><span class=line> <span class=comment>// 这里如果state还是0说明锁还空着</span></span><br><span class=line> <span class=keyword>if</span> (c == <span class=number>0</span>) {</span><br><span class=line> <span class=comment>// 因为是公平锁版本的,先去看下是否阻塞队列里有排着队的</span></span><br><span class=line> <span class=keyword>if</span> (!hasQueuedPredecessors() &&</span><br><span class=line> compareAndSetState(<span class=number>0</span>, acquires)) {</span><br><span class=line> <span class=comment>// 没有排队的,并且state使用cas设置成功的就标记当前占有锁的线程是我</span></span><br><span class=line> setExclusiveOwnerThread(current);</span><br><span class=line> <span class=comment>// 然后其实就返回了,包括阻塞队列的head和tail节点和waitStatus都没有设置</span></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 class=keyword>else</span> <span class=keyword>if</span> (current == getExclusiveOwnerThread()) {</span><br><span class=line> <span class=type>int</span> <span class=variable>nextc</span> <span class=operator>=</span> c + acquires;</span><br><span class=line> <span class=keyword>if</span> (nextc < <span class=number>0</span>)</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">Error</span>(<span class=string>"Maximum lock count exceeded"</span>);</span><br><span class=line> setState(nextc);</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 class=comment>// 这里就是第二个线程会返回false</span></span><br><span class=line> <span class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> }</span><br><span class=line> }</span><br></pre></table></figure><h2 id=第二个线程><a class=headerlink href=#第二个线程 title=第二个线程></a>第二个线程</h2><p>当第二个线程进来的时候应该是怎么样,结合代码来看<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></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Acquires in exclusive mode, ignoring interrupts. Implemented</span></span><br><span class=line><span class=comment> * by invoking at least once {<span class=doctag>@link</span> #tryAcquire},</span></span><br><span class=line><span class=comment> * returning on success. Otherwise the thread is queued, possibly</span></span><br><span class=line><span class=comment> * repeatedly blocking and unblocking, invoking {<span class=doctag>@link</span></span></span><br><span class=line><span class=comment> * #tryAcquire} until success. This method can be used</span></span><br><span class=line><span class=comment> * to implement method {<span class=doctag>@link</span> Lock#lock}.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> arg the acquire argument. This value is conveyed to</span></span><br><span class=line><span class=comment> * {<span class=doctag>@link</span> #tryAcquire} but is otherwise uninterpreted and</span></span><br><span class=line><span class=comment> * can represent anything you like.</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_">acquire</span><span class=params>(<span class=type>int</span> arg)</span> {</span><br><span class=line> <span class=comment>// 前面第一种情况是tryAcquire直接成功了,这个if判断第一个条件就是false,就不往下执行了</span></span><br><span class=line> <span class=comment>// 如果是第二个线程,第一个条件获取锁不成功,条件判断!tryAcquire(arg) == true,就会走</span></span><br><span class=line> <span class=comment>// acquireQueued(addWaiter(Node.EXCLUSIVE), arg)</span></span><br><span class=line> <span class=keyword>if</span> (!tryAcquire(arg) &&</span><br><span class=line> acquireQueued(addWaiter(Node.EXCLUSIVE), arg))</span><br><span class=line> selfInterrupt();</span><br><span class=line> }</span><br></pre></table></figure><p>然后来看下addWaiter的逻辑<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> * Creates and enqueues node for current thread and given mode.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> the new 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_">addWaiter</span><span class=params>(Node mode)</span> {</span><br><span class=line> <span class=comment>// 这里是包装成一个node</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(), mode);</span><br><span class=line> <span class=comment>// Try the fast path of enq; backup to full enq on failure</span></span><br><span class=line> <span class=comment>// 最快的方式就是把当前线程的节点放在阻塞队列的最后</span></span><br><span class=line> <span class=type>Node</span> <span class=variable>pred</span> <span class=operator>=</span> tail;</span><br><span class=line> <span class=comment>// 只有当tail,也就是pred不为空的时候可以直接接上</span></span><br><span class=line> <span class=keyword>if</span> (pred != <span class=literal>null</span>) {</span><br><span class=line> node.prev = pred;</span><br><span class=line> <span class=comment>// 如果这里cas成功了,就直接接上返回了</span></span><br><span class=line> <span class=keyword>if</span> (compareAndSetTail(pred, node)) {</span><br><span class=line> pred.next = node;</span><br><span class=line> <span class=keyword>return</span> node;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> <span class=comment>// 不然就会继续走到这里</span></span><br><span class=line> enq(node);</span><br><span class=line> <span class=keyword>return</span> node;</span><br><span class=line> }</span><br></pre></table></figure><p>然后就是enq的逻辑了<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> * Inserts node into queue, initializing if necessary. See picture above.</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> node the node to insert</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> node's predecessor</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_">enq</span><span class=params>(<span class=keyword>final</span> Node node)</span> {</span><br><span class=line> <span class=keyword>for</span> (;;) {</span><br><span class=line> <span class=comment>// 如果状态没变化的话,tail这时还是null的</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=keyword>if</span> (t == <span class=literal>null</span>) { <span class=comment>// Must initialize</span></span><br><span class=line> <span class=comment>// 这里就会初始化头结点,就是个空节点</span></span><br><span class=line> <span class=keyword>if</span> (compareAndSetHead(<span class=keyword>new</span> <span class="title class_">Node</span>()))</span><br><span class=line> <span class=comment>// tail也赋值成head</span></span><br><span class=line> tail = head;</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=comment>// 这里就设置tail了</span></span><br><span class=line> node.prev = t;</span><br><span class=line> <span class=keyword>if</span> (compareAndSetTail(t, node)) {</span><br><span class=line> t.next = node;</span><br><span class=line> <span class=keyword>return</span> t;</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><p>所以从这里可以看出来,其实head头结点不是个真实的带有线程的节点,并且不是在第一个线程进来的时候设置的<h2 id=解锁><a class=headerlink href=#解锁 title=解锁></a>解锁</h2><p>通过代码来看下<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></pre><td class=code><pre><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Attempts to release this lock.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * &LTp>If the current thread is the holder of this lock then the hold</span></span><br><span class=line><span class=comment> * count is decremented. If the hold count is now zero then the lock</span></span><br><span class=line><span class=comment> * is released. If the current thread is not the holder of this</span></span><br><span class=line><span class=comment> * lock then {<span class=doctag>@link</span> IllegalMonitorStateException} is thrown.</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 the current thread does not</span></span><br><span class=line><span class=comment> * hold this lock</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line> <span class=keyword>public</span> <span class=keyword>void</span> <span class="title function_">unlock</span><span class=params>()</span> {</span><br><span class=line> <span class=comment>// 释放锁</span></span><br><span class=line> sync.release(<span class=number>1</span>);</span><br><span class=line> }</span><br><span class=line><span class=comment>/**</span></span><br><span class=line><span class=comment> * Releases in exclusive mode. Implemented by unblocking one or</span></span><br><span class=line><span class=comment> * more threads if {<span class=doctag>@link</span> #tryRelease} returns true.</span></span><br><span class=line><span class=comment> * This method can be used to implement method {<span class=doctag>@link</span> Lock#unlock}.</span></span><br><span class=line><span class=comment> *</span></span><br><span class=line><span class=comment> * <span class=doctag>@param</span> arg the release argument. This value is conveyed to</span></span><br><span class=line><span class=comment> * {<span class=doctag>@link</span> #tryRelease} but is otherwise uninterpreted and</span></span><br><span class=line><span class=comment> * can represent anything you like.</span></span><br><span class=line><span class=comment> * <span class=doctag>@return</span> the value returned from {<span class=doctag>@link</span> #tryRelease}</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=type>boolean</span> <span class="title function_">release</span><span class=params>(<span class=type>int</span> arg)</span> {</span><br><span class=line> <span class=comment>// 尝试去释放</span></span><br><span class=line> <span class=keyword>if</span> (tryRelease(arg)) {</span><br><span class=line> <span class=type>Node</span> <span class=variable>h</span> <span class=operator>=</span> head;</span><br><span class=line> <span class=keyword>if</span> (h != <span class=literal>null</span> && h.waitStatus != <span class=number>0</span>)</span><br><span class=line> unparkSuccessor(h);</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 class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> }</span><br><span class=line><span class=keyword>protected</span> <span class=keyword>final</span> <span class=type>boolean</span> <span class="title function_">tryRelease</span><span class=params>(<span class=type>int</span> releases)</span> {</span><br><span class=line> <span class=type>int</span> <span class=variable>c</span> <span class=operator>=</span> getState() - releases;</span><br><span class=line> <span class=keyword>if</span> (Thread.currentThread() != getExclusiveOwnerThread())</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=type>boolean</span> <span class=variable>free</span> <span class=operator>=</span> <span class=literal>false</span>;</span><br><span class=line> <span class=comment>// 判断是否完全释放锁,因为可重入</span></span><br><span class=line> <span class=keyword>if</span> (c == <span class=number>0</span>) {</span><br><span class=line> free = <span class=literal>true</span>;</span><br><span class=line> setExclusiveOwnerThread(<span class=literal>null</span>);</span><br><span class=line> }</span><br><span class=line> setState(c);</span><br><span class=line> <span class=keyword>return</span> free;</span><br><span class=line> }</span><br><span class=line><span class=comment>// 这段代码和上面的一致,只是为了顺序性,又拷下来看下</span></span><br><span class=line></span><br><span class=line><span class=keyword>public</span> <span class=keyword>final</span> <span class=type>boolean</span> <span class="title function_">release</span><span class=params>(<span class=type>int</span> arg)</span> {</span><br><span class=line> <span class=comment>// 尝试去释放,如果是完全释放,返回的就是true,否则是false</span></span><br><span class=line> <span class=keyword>if</span> (tryRelease(arg)) {</span><br><span class=line> <span class=type>Node</span> <span class=variable>h</span> <span class=operator>=</span> head;</span><br><span class=line> <span class=comment>// 这里判断头结点是否为空以及waitStatus的状态,前面说了head节点其实是</span></span><br><span class=line> <span class=comment>// 在第二个线程进来的时候初始化的,如果是空的话说明没后续节点,并且waitStatus</span></span><br><span class=line> <span class=comment>// 也表示了后续的等待状态</span></span><br><span class=line> <span class=keyword>if</span> (h != <span class=literal>null</span> && h.waitStatus != <span class=number>0</span>)</span><br><span class=line> unparkSuccessor(h);</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 class=keyword>return</span> <span class=literal>false</span>;</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> * Wakes up node's successor, if one exists.</span></span><br><span class=line><span class=comment> *</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></span><br><span class=line><span class=comment>// 唤醒后继节点</span></span><br><span class=line> <span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">unparkSuccessor</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 status is negative (i.e., possibly needing signal) try</span></span><br><span class=line><span class=comment> * to clear in anticipation of signalling. It is OK if this</span></span><br><span class=line><span class=comment> * fails or if status is changed by waiting thread.</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line> <span class=type>int</span> <span class=variable>ws</span> <span class=operator>=</span> node.waitStatus;</span><br><span class=line> <span class=keyword>if</span> (ws < <span class=number>0</span>)</span><br><span class=line> compareAndSetWaitStatus(node, ws, <span class=number>0</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>/*</span></span><br><span class=line><span class=comment> * Thread to unpark is held in successor, which is normally</span></span><br><span class=line><span class=comment> * just the next node. But if cancelled or apparently null,</span></span><br><span class=line><span class=comment> * traverse backwards from tail to find the actual</span></span><br><span class=line><span class=comment> * non-cancelled successor.</span></span><br><span class=line><span class=comment> */</span></span><br><span class=line> <span class=type>Node</span> <span class=variable>s</span> <span class=operator>=</span> node.next;</span><br><span class=line> <span class=comment>// 如果后继节点是空或者当前节点取消等待了</span></span><br><span class=line> <span class=keyword>if</span> (s == <span class=literal>null</span> || s.waitStatus > <span class=number>0</span>) {</span><br><span class=line> s = <span class=literal>null</span>;</span><br><span class=line> <span class=comment>// 从后往前找,找到非取消的节点,注意这里不是找到就退出,而是一直找到头</span></span><br><span class=line> <span class=comment>// 所以不必担心中间有取消的</span></span><br><span class=line> <span class=keyword>for</span> (<span class=type>Node</span> <span class=variable>t</span> <span class=operator>=</span> tail; t != <span class=literal>null</span> && t != node; t = t.prev)</span><br><span class=line> <span class=keyword>if</span> (t.waitStatus <= <span class=number>0</span>)</span><br><span class=line> s = t;</span><br><span class=line> }</span><br><span class=line> <span class=keyword>if</span> (s != <span class=literal>null</span>)</span><br><span class=line> <span class=comment>// 将其唤醒</span></span><br><span class=line> LockSupport.unpark(s.thread);</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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