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<h1 id="RunLoop内部实现"><a href="#RunLoop内部实现" class="headerlink" title="RunLoop内部实现"></a>RunLoop内部实现</h1><h2 id="内部逻辑"><a href="#内部逻辑" class="headerlink" title="内部逻辑"></a>内部逻辑</h2><p>根据苹果在文档里的说明，RunLoop 内部的逻辑大致如下:</p>
<p><img src="https://ws3.sinaimg.cn/large/006tNc79ly1g2bql5ppdrj30hz0dun06.jpg" alt=""></p>
<p>RunLoop的事件队列,官方描述<a href="https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Multithreading/RunLoopManagement/RunLoopManagement.html#//apple_ref/doc/uid/10000057i-CH16-SW23" target="_blank" rel="noopener">看这里</a></p>
<blockquote>
<ol>
<li>通知观察者run loop已经启动</li>
</ol>
<ul>
<li>通知观察者任何即将要开始的定时器</li>
<li>通知观察者任何即将启动的非基于端口的源</li>
<li>启动任何准备好的非基于端口的源</li>
<li>如果基于端口的源准备好并处于等待状态，立即启动；并进入步骤9。</li>
<li>通知观察者线程进入休眠</li>
<li>将线程置于休眠直到任一下面的事件发生：<ul>
<li>某一事件到达基于端口的源</li>
<li>定时器启动</li>
<li>Run loop设置的时间已经超时</li>
<li>run loop被显式唤醒</li>
</ul>
</li>
<li>通知观察者线程将被唤醒。</li>
<li>处理未处理的事件<ul>
<li>如果用户定义的定时器启动，处理定时器事件并重启run loop。进入步骤2</li>
<li>如果输入源启动，传递相应的消息</li>
<li>如果run loop被显式唤醒而且时间还没超时，重启run loop。进入步骤2</li>
</ul>
</li>
<li>通知观察者run loop结束。</li>
</ul>
</blockquote>
<p>其内部代码整理如下 ：<br><figure class="highlight c"><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></pre></td><td class="code"><pre><span class="line"><span class="comment">/// 用DefaultMode启动</span></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">CFRunLoopRun</span><span class="params">(<span class="keyword">void</span>)</span> </span>{</span><br><span class="line"> CFRunLoopRunSpecific(CFRunLoopGetCurrent(), kCFRunLoopDefaultMode, <span class="number">1.0e10</span>, <span class="literal">false</span>);</span><br><span class="line">}</span><br><span class="line"> </span><br><span class="line"><span class="comment">/// 用指定的Mode启动，允许设置RunLoop超时时间</span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">CFRunLoopRunInMode</span><span class="params">(CFStringRef modeName, CFTimeInterval seconds, Boolean stopAfterHandle)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> CFRunLoopRunSpecific(CFRunLoopGetCurrent(), modeName, seconds, returnAfterSourceHandled);</span><br><span class="line">}</span><br><span class="line"> </span><br><span class="line"><span class="comment">/// RunLoop的实现</span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">CFRunLoopRunSpecific</span><span class="params">(runloop, modeName, seconds, stopAfterHandle)</span> </span>{</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 首先根据modeName找到对应mode</span></span><br><span class="line"> CFRunLoopModeRef currentMode = __CFRunLoopFindMode(runloop, modeName, <span class="literal">false</span>);</span><br><span class="line"> <span class="comment">/// 如果mode里没有source/timer/observer, 直接返回。</span></span><br><span class="line"> <span class="keyword">if</span> (__CFRunLoopModeIsEmpty(currentMode)) <span class="keyword">return</span>;</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 1. 通知 Observers: RunLoop 即将进入 loop。</span></span><br><span class="line"> __CFRunLoopDoObservers(runloop, currentMode, kCFRunLoopEntry);</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 内部函数，进入loop</span></span><br><span class="line"> __CFRunLoopRun(runloop, currentMode, seconds, returnAfterSourceHandled) {</span><br><span class="line"> </span><br><span class="line"> Boolean sourceHandledThisLoop = NO;</span><br><span class="line"> <span class="keyword">int</span> retVal = <span class="number">0</span>;</span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 2. 通知 Observers: RunLoop 即将触发 Timer 回调。</span></span><br><span class="line"> __CFRunLoopDoObservers(runloop, currentMode, kCFRunLoopBeforeTimers);</span><br><span class="line"> <span class="comment">/// 3. 通知 Observers: RunLoop 即将触发 Source0 (非port) 回调。</span></span><br><span class="line"> __CFRunLoopDoObservers(runloop, currentMode, kCFRunLoopBeforeSources);</span><br><span class="line"> <span class="comment">/// 执行被加入的block</span></span><br><span class="line"> __CFRunLoopDoBlocks(runloop, currentMode);</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 4. RunLoop 触发 Source0 (非port) 回调。</span></span><br><span class="line"> sourceHandledThisLoop = __CFRunLoopDoSources0(runloop, currentMode, stopAfterHandle);</span><br><span class="line"> <span class="comment">/// 执行被加入的block</span></span><br><span class="line"> __CFRunLoopDoBlocks(runloop, currentMode);</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 5. 如果有 Source1 (基于port) 处于 ready 状态，直接处理这个 Source1 然后跳转去处理消息。</span></span><br><span class="line"> <span class="keyword">if</span> (__Source0DidDispatchPortLastTime) {</span><br><span class="line"> Boolean hasMsg = __CFRunLoopServiceMachPort(dispatchPort, &msg)</span><br><span class="line"> <span class="keyword">if</span> (hasMsg) <span class="keyword">goto</span> handle_msg;</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 通知 Observers: RunLoop 的线程即将进入休眠(sleep)。</span></span><br><span class="line"> <span class="keyword">if</span> (!sourceHandledThisLoop) {</span><br><span class="line"> __CFRunLoopDoObservers(runloop, currentMode, kCFRunLoopBeforeWaiting);</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 7. 调用 mach_msg 等待接受 mach_port 的消息。线程将进入休眠, 直到被下面某一个事件唤醒。</span></span><br><span class="line"> <span class="comment">/// 一个基于 port 的Source 的事件。</span></span><br><span class="line"> <span class="comment">/// 一个 Timer 到时间了</span></span><br><span class="line"> <span class="comment">/// RunLoop 自身的超时时间到了</span></span><br><span class="line"> <span class="comment">/// 被其他什么调用者手动唤醒</span></span><br><span class="line"> __CFRunLoopServiceMachPort(waitSet, &msg, <span class="keyword">sizeof</span>(msg_buffer), &livePort) {</span><br><span class="line"> mach_msg(msg, MACH_RCV_MSG, port); <span class="comment">// thread wait for receive msg</span></span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 8. 通知 Observers: RunLoop 的线程刚刚被唤醒了。</span></span><br><span class="line"> __CFRunLoopDoObservers(runloop, currentMode, kCFRunLoopAfterWaiting);</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 收到消息，处理消息。</span></span><br><span class="line"> handle_msg:</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 9.1 如果一个 Timer 到时间了，触发这个Timer的回调。</span></span><br><span class="line"> <span class="keyword">if</span> (msg_is_timer) {</span><br><span class="line"> __CFRunLoopDoTimers(runloop, currentMode, mach_absolute_time())</span><br><span class="line"> } </span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 9.2 如果有dispatch到main_queue的block，执行block。</span></span><br><span class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (msg_is_dispatch) {</span><br><span class="line"> __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(msg);</span><br><span class="line"> } </span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 9.3 如果一个 Source1 (基于port) 发出事件了，处理这个事件</span></span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> CFRunLoopSourceRef source1 = __CFRunLoopModeFindSourceForMachPort(runloop, currentMode, livePort);</span><br><span class="line"> sourceHandledThisLoop = __CFRunLoopDoSource1(runloop, currentMode, source1, msg);</span><br><span class="line"> <span class="keyword">if</span> (sourceHandledThisLoop) {</span><br><span class="line"> mach_msg(reply, MACH_SEND_MSG, reply);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 执行加入到Loop的block</span></span><br><span class="line"> __CFRunLoopDoBlocks(runloop, currentMode);</span><br><span class="line"> </span><br><span class="line"> </span><br><span class="line"> <span class="keyword">if</span> (sourceHandledThisLoop && stopAfterHandle) {</span><br><span class="line"> <span class="comment">/// 进入loop时参数说处理完事件就返回。</span></span><br><span class="line"> retVal = kCFRunLoopRunHandledSource;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (timeout) {</span><br><span class="line"> <span class="comment">/// 超出传入参数标记的超时时间了</span></span><br><span class="line"> retVal = kCFRunLoopRunTimedOut;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (__CFRunLoopIsStopped(runloop)) {</span><br><span class="line"> <span class="comment">/// 被外部调用者强制停止了</span></span><br><span class="line"> retVal = kCFRunLoopRunStopped;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (__CFRunLoopModeIsEmpty(runloop, currentMode)) {</span><br><span class="line"> <span class="comment">/// source/timer/observer一个都没有了</span></span><br><span class="line"> retVal = kCFRunLoopRunFinished;</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 如果没超时，mode里没空，loop也没被停止，那继续loop。</span></span><br><span class="line"> } <span class="keyword">while</span> (retVal == <span class="number">0</span>);</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/// 10. 通知 Observers: RunLoop 即将退出。</span></span><br><span class="line"> __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit);</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>可以看到，实际上 RunLoop 就是这样一个函数，其内部是一个 do-while 循环。当你调用 CFRunLoopRun() 时，线程就会一直停留在这个循环里；直到超时或被手动停止，该函数才会返回。</p>
<p>这张图更详细描述了上面Runloop的核心流程：<br><img src="https://ws2.sinaimg.cn/large/006tNc79ly1g2bql66rcsj30u00ul0xx.jpg" alt=""></p>
<blockquote>
<p>注意：</p>
<ul>
<li>是_黄色_区域的消息处理中并不包含source0，因为它在循环开始之初就会处理</li>
<li>CFRunLoopPerformBlock尽管在上图中作为唤醒机制有所体现，但事实上执行只是入队，等待下次RunLoop运行才会执行，而如果需要立即执行则必须调用CFRunLoopWakeUp。</li>
</ul>
</blockquote>
<h2 id="底层实现"><a href="#底层实现" class="headerlink" title="底层实现"></a>底层实现</h2><p>从上面代码第7步可以看到，RunLoop 的核心是基于 mach port 的，其进入休眠时调用的函数是 <code>mach_msg()</code>。</p>
<figure class="highlight less"><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></pre></td><td class="code"><pre><span class="line"><span class="comment">/// 7. 调用 mach_msg 等待接受 mach_port 的消息。线程将进入休眠, 直到被下面某一个事件唤醒。</span></span><br><span class="line"><span class="comment">/// 一个基于 port 的Source 的事件。</span></span><br><span class="line"><span class="comment">/// 一个 Timer 到时间了</span></span><br><span class="line"><span class="comment">/// RunLoop 自身的超时时间到了</span></span><br><span class="line"><span class="comment">/// 被其他什么调用者手动唤醒</span></span><br><span class="line"><span class="selector-tag">__CFRunLoopServiceMachPort</span>(waitSet, &msg, sizeof(msg_buffer), &livePort) {</span><br><span class="line"> <span class="selector-tag">mach_msg</span>(msg, MACH_RCV_MSG, port); <span class="comment">// thread wait for receive msg</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><img src="https://ws3.sinaimg.cn/large/006tNc79ly1g2bql73mjlj30ni0bct9b.jpg" alt="OSX/iOS 这个核心的架构"></p>
<ul>
<li><p>Mach 是 Darwin 的核心，可以说是内核的核心，提供了进程间通信（IPC）、处理器调度等基础服务。在 Mach 中，进程、线程间的通信是以消息的方式来完成的，消息在两个 Port 之间进行传递（这也正是 Source1 之所以称之为 Port-based Source 的原因，因为它就是依靠系统发送消息到指定的Port来触发的）。消息的发送和接收使用<mach/message.h>中的mach_msg()函数</p>
</li>
<li><p>为了实现消息的发送和接收，<code>mach_msg()</code> 函数实际上是调用了一个 Mach 陷阱 (trap)，即函数<code>mach_msg_trap()</code>，陷阱这个概念在 Mach 中等同于系统调用。当你在用户态调用 <code>mach_msg_trap()</code> 时会触发陷阱机制，切换到内核态；内核态中内核实现的 mach_msg() 函数会完成实际的工作，如下图：<br><img src="https://ws2.sinaimg.cn/large/006tNc79ly1g2bql7ymgfj306j05ejrf.jpg" alt=""><br>例如你在模拟器里跑起一个 iOS 的 App，然后在 App 静止时点击暂停，你会看到主线程调用栈是停留在 <code>mach_msg_trap()</code> 这个地方</p>
</li>
</ul>
<p>关于具体 mach port 发送信息可以查看：NSHipster这篇<a href="http://nshipster.com/inter-process-communication/" target="_blank" rel="noopener">文章</a>，或<a href="http://segmentfault.com/a/1190000002400329" target="_blank" rel="noopener">中文翻译</a> 。</p>
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<div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#RunLoop内部实现"><span class="nav-number">1.</span> <span class="nav-text">RunLoop内部实现</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#内部逻辑"><span class="nav-number">1.1.</span> <span class="nav-text">内部逻辑</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#底层实现"><span class="nav-number">1.2.</span> <span class="nav-text">底层实现</span></a></li></ol></li></ol></div>
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