Chromium中多线程及并发技术要点(C/C++)

﹏ヽ暗。殇╰゛Y 2022-08-19 08:52 9阅读 0赞

<table> 
 <tbody> 
  <tr> 
   <th colspan="1">类别</th> 
   <th colspan="1">类</th> 
   <th colspan="1">说明</th> 
   <th colspan="1">示例</th> 
  </tr> 
  <tr> 
   <td colspan="1"><p>线程机制</p></td> 
   <td colspan="1">Thread</td> 
   <td colspan="1">(参考:<a href="http://blog.csdn.net/horkychen/article/details/50486062" rel="nofollow">线程模型及应用指南</a>)<br><img src="https://img-blog.csdn.net/20160109004418670?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" width="300" height="150"><br></td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">MessagePump</td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">MessageQueue</td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">SequencedWorkerPool</td> 
   <td colspan="1"> 
    <div>
      它是一个线程池，用于执行需要串行执行的任务请求，这些请求依据不同的Token分组，只在相同组内保证执行顺序。 
    </div> 
    <div>
      这样多个组可以并行执行，而单个组则是串行执行。比如：不同实例所对应的分组不同，或者不同的功能对应不同的分组。 
    </div> 
    <div>
      它同时允许指定当退出时未执行的任务如何处理，包括:继续执行，忽略，阻止退出。 
    </div> 
    <div>
      参考: 
     <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/OaA-9rnjOqI" rel="nofollow">The FILE thread is dead, long live the blocking pool</a>. 
    </div></td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">并发控制机制</td> 
   <td colspan="1">volatile</td> 
   <td colspan="1"><p>语言基于处理器提供的特性。保证各个线程读数据时为最新的值。但它的使用需要掌握一定的技巧。</p><p>参考:&nbsp;<a href="http://hedengcheng.com/?p=725" rel="nofollow">C/C++ Volatile关键字深度剖析</a></p></td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1"><p>Atomic32&nbsp;</p><p>(base/atomicops.h)</p><p>AtomicSequenceNumber (base/atomic_sequence_num.h)</p><p>AtomicRefCountXxx</p><p>(base/atomic_ref_count.h)</p></td> 
   <td colspan="1">Chromium提供的原子数据类型。</td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1"><p><strong>AutoLock</strong></p><p><strong>AutoUnlock</strong></p><p>Lock</p><p>(base/synchronization/lock.h)</p></td> 
   <td colspan="1"><p>非常接近于Java的<strong>Synchronized</strong>。Lock和AutoLock很好理解。AutoUnlock的行为</p><p>与AutoLock相似，建构时release lock, 在析构时acquire lock.</p><p>*应用了RAII idiom。</p></td> 
   <td colspan="1"><p>cookie_manager.cc</p><p>*AutoUnlock的示例:</p><p>media/filters/audio_renderer_impl.h</p> 
    <div> 
     <div> 
      <div></div> 
     </div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">WaitableEvent<br>(base/synchronization/waitable_event.h)</td> 
   <td colspan="1"><p>以异步的调用完成操作，在调用端以一个WaitableEvent等待任务完成.</p><p>基于Lock + ConditionVariable实现。</p></td> 
   <td colspan="1"> 
    <div> 
     <br> 
    </div> 
    <div> 
     <div></div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">ConditionVariable<br>(base/synchronization/condition_variable.h)</td> 
   <td colspan="1"><p>条件变量的C/C++实现。主要方法:</p> 
    <div>
      &nbsp; &nbsp; &nbsp;Wait 
    </div> 
    <div>
      &nbsp; &nbsp; &nbsp;TimeWait 
    </div> 
    <div>
      &nbsp; &nbsp; &nbsp;BroadCast 
    </div> 
    <div>
      &nbsp; &nbsp; &nbsp;Singal&nbsp; 
    </div></td> 
   <td colspan="1"><p>InProcessCommandBuffer</p> 
    <div> 
     <div> 
      <div></div> 
     </div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">CancellationFlag<br>(base/synchronization/cancellation_flag.h)</td> 
   <td colspan="1">基于原子操作，提供一个布尔值标志的设定和查询。</td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">WTF提供的机制</td> 
   <td colspan="1">atomicXXX<br>(wtf/Atomics.h)</td> 
   <td colspan="1">WebKit提供的原子类</td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">Mutex<br>(wtf/TreadingPrimitives.h)</td> 
   <td colspan="1">互斥量的实现 (对平台化的抽象)<br>和base中的Lock系列相似。</td> 
   <td colspan="1"><p>Mutex m_mutex;</p><p>{ <br>&nbsp; MutexLocker locker(m_mutex);</p><p>&nbsp; ......</p><p>}</p></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1"><p>MutexLock</p><p>(wtf/TreadingPrimitives.h)</p></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">RecursiveMutex<br>(wtf/TreadingPrimitives.h)</td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">MutexTryLocker (wtf/TreadingPrimitives.h)</td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">ThreadCondition<br>(wtf/TreadingPrimitives.h)</td> 
   <td colspan="1">条件变量的实现</td> 
   <td colspan="1">&nbsp;</td> 
  </tr> 
  <tr> 
   <td colspan="1">并发容器</td> 
   <td colspan="1"><p>ThreadLocalBoolean</p><p>ThreadLocalPointer</p><p>(base/threading/thread_local.h)</p></td> 
   <td colspan="1">TLS (Thread Local Stoage) 的实现</td> 
   <td colspan="1"> 
    <div>
      在ThreadRestrictions中有ThreadLocal的应用: 
    </div> 
    <div>
      LazyInstance&lt;ThreadLocalBoolean&gt;::Leaky 
    </div> 
    <div>
      &nbsp; &nbsp; g_io_disallowed&nbsp;=&nbsp;LAZY_INSTANCE_INITIALIZER;&nbsp; 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">ThreadSafeDataTransport<br>&nbsp;(wtf/ThreadSafeDataTransport.h)</td> 
   <td colspan="1">以线程安全的方式在一对生产者和消费者之间利用SharedBuffer传递数据。减少线程冲突和数据拷贝。</td> 
   <td colspan="1"><p>ImageFrameGenerator.h</p> 
    <div> 
     <div>
       &nbsp; 更多的说明 
     </div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">LazyInstance</td> 
   <td colspan="1"><p>函数中静态成员初始化不是线程安全的，容易出现隐患 (C++11已经声称可以保证)。可以使用base::LazyInstance()来解决, 同时LazyInstance可以避免内存碎片，因为它的对象都是在数据段创建的。</p><p>参考:<a href="https://groups.google.com/a/chromium.org/forum/#!msg/chromium-dev/p6h3HC8Wro4/HHBMg7fYiMYJ" rel="nofollow">Eliminating static initializers</a>.</p></td> 
   <td colspan="1"><p><br></p> 
    <div> 
     <div> 
      <div></div> 
     </div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">工具类</td> 
   <td colspan="1">NonThreadSafe</td> 
   <td colspan="1"><p>只在Debug下有效。提供非线程安全对象的保护机制。即创建及使用在同一线程上。</p><p>主要方法: CalledOnValidThread()</p></td> 
   <td colspan="1"><p>RefCountedBase在最新 Chromium分支也是继承自NonThreadSafe。</p> 
    <div> 
     <div> 
      <div></div> 
     </div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1"><p>ThreadCollisionWarner</p><p>&nbsp;(base/threading/thread_collision_warner.h)</p></td> 
   <td colspan="1"><p>提供一组宏，用于帮助保证类的线程安全。这个源于线程问题预防的机制，在编码层面防止线程问题。细节参考:&nbsp;<a href="http://cpp-today.blogspot.it/2008/06/threading-mess.html" rel="nofollow">"Threading mess"</a>。</p><p>主要提供的机制包括:</p> 
    <ol> 
     <li>DFAKE_SCOPED_LOCK, 限制某个函数只能在一个线程上运行。</li> 
     <li>DFAKE_SCOPED_RECURSIVE_LOCK, 多个函数可以在同一线程上嵌套调用。</li> 
     <li>DFAKE_SCOPED_LOCK_THREAD_LOCKED, 同时只允许一个函数运行在相同的线程上。包括创建和释放应当在同一线程上。</li> 
    </ol></td> 
   <td colspan="1"> 
    <div> 
     <br> 
    </div> 
    <div> 
     <div></div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">ThreadChecker <br>(base/threading/thread_checker.h)</td> 
   <td colspan="1"><p>对一个非线程安全的类，为了确保它的实例不会被跨线程进行操作，就可以使用一个ThreadChecker成员变量来进行保证。</p><p>*只在Debug模式下生效。</p></td> 
   <td colspan="1"> 
    <div> 
     <br> 
    </div> 
    <div> 
     <div></div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">ThreadRestrictions <br>(base/threading/thread_restrictions.h)</td> 
   <td colspan="1"> 
    <div>
      为每个线程增加限制条件。如不允许阻塞I/O, 是否允许单例对象等。 
    </div> 
    <div>
      &nbsp; 以单例为例，它会在base::Singleton::get()检查。 
    </div> 
    <div>
      &nbsp; 而IO的检查，则在各个IO处理的函数中检查，如LoadNativeLibrary(),&nbsp;SysInfo::AmountOfFreeDiskSpace(),&nbsp;OpenFile()等。&nbsp; 
    </div></td> 
   <td colspan="1"> 
    <div> 
     <div> 
      <div> 
       <table> 
        <tbody> 
         <tr> 
          <td colspan="1"> 
           <div title="Hint: double-click to select code"> 
            <div> 
             <code>FILE* OpenFile(</code> 
             <code>const</code> 
             <code>FilePath&amp; filename, </code> 
             <code>const</code> 
             <code>char</code> 
             <code>* mode) { </code> 
            </div> 
            <div> 
             <code>&nbsp;&nbsp;</code> 
             <code>ThreadRestrictions::AssertIOAllowed();</code> 
            </div> 
            <div> 
             <code>&nbsp;&nbsp;</code> 
             <code>…...</code> 
            </div> 
            <div> 
             <code>}</code> 
            </div> 
           </div></td> 
         </tr> 
        </tbody> 
       </table> 
      </div> 
     </div> 
    </div></td> 
  </tr> 
  <tr> 
   <td colspan="1">&nbsp;</td> 
   <td colspan="1">WatchDog <br>(base/threading/watchdog.h)</td> 
   <td colspan="1">用于监测某个线程在指定时间没有响应的情况。主要方法Arm()及Disarm()。</td> 
   <td colspan="1"> 
    <div>
      在UMA中: 
    </div> 
    <div>
      class&nbsp;ShutdownWatchDogThread&nbsp;:&nbsp;public&nbsp;base::Watchdog&nbsp;{&nbsp; 
    </div> 
    <div>
      …... 
    </div> 
    <div>
      }&nbsp; 
    </div></td> 
  </tr> 
 </tbody> 
</table>

\*C++11 thread尚未使用。