如何解锁 boost::upgrade_to_unique_lock （由 boost::shared_mutex 制成）？

【问题标题】：How to unlock boost::upgrade_to_unique_lock (made from boost::shared_mutex)?如何解锁 boost::upgrade_to_unique_lock （由 boost::shared_mutex 制成）？
【发布时间】：2011-10-09 16:28:58
【问题描述】：

所以我有一些 shared_mutex 并这样做了：

        boost::upgrade_lock<boost::shared_mutex> lock(f->mutex);
        boost::upgrade_to_unique_lock<boost::shared_mutex> uniqueLock(lock);

现在我想“解锁”或至少将其降级为：

boost::shared_lock<boost::shared_mutex> lock_r(f->mutex);

这样的事情怎么办？有可能吗？

【问题讨论】：

标签： c++ multithreading boost locking mutex

【解决方案1】：

如果您让upgrade_to_unique_lock 超出范围，它将自动降级回升级所有权。

例如

void foo() {
   boost::upgrade_lock<boost::shared_mutex> lock(f->mutex);

   // Do shared operations, as mutex is held upgradeable
   // ...

   if(need_to_get_unique)
   {
      boost::upgrade_to_unique_lock<boost::shared_mutex> uniqueLock(lock); 

      // Do exclusive operations, as mutex is held uniquely
      // ... 
      // At end of scope unique is released back to upgradeable
   }
   // Only shared operations here, as it's only held upgradeable
   // ...

   // At end of scope mutex is completely released
}

编辑：另一件事。如果给定的函数只需要独占锁，您可以使用boost::unique_lock 和唯一锁，而无需同时使用upgrade 和upgrade_to_unique 锁。

【讨论】：