如何在VC ++中获取WPF应用程序的屏幕截图？(How to get screenshot of WPF application in VC++?)

 标准没有给出这样的保证， notify_one可以唤醒当前正在等待的任何线程（§30.5.1）： 
 
 
 
 void notify_one() noexcept; 效果：如果有任何线程被阻塞等待*this ，则取消阻止其中一个theads。 
 
 
 确保特定线程对事件做出反应的唯一方法是唤醒所有线程，然后使用一些额外的同步机制将除了正确的线程之外的所有线程发送回休眠状态。 
 
 由于平台必须满足的要求，这是一个基本限制：通常条件变量以等待线程进入挂起状态的方式实现，并且在发生通知之前不会再次由系统调度。 不需要调度程序实现来提供用于选择用于唤醒的特定线程的功能（并且许多实际上没有）。 
 
 所以逻辑的这一部分不可避免地必须由用户代码处理，这反过来意味着你必须唤醒所有线程以使其工作，因为这是确保正确的线程将被唤醒的唯一方法。 

No such guarantess are given by the standard, notify_one may wake any thread that is currently waiting (§30.5.1):
 
 
 
void notify_one() noexcept; Effects: If any threads are blocked waiting for *this, unblocks one of those theads.
 
 
The only way to ensure that a specific thread reacts to the event is to wake all threads and then have some additional synchronization mechanism that sends all but the correct thread back to sleep.
 
This is a fundamental limitation due to the requirements that the platform has to fulfill: Usually condition variables are implemented in a way that the waiting threads are put into a suspended state and will not get scheduled by the system again until a notify occurs. A scheduler implementation is not required to provide the functionality for selecting a specific thread for waking up (and many actually don't).
 
So this part of the logic inevitably has to be handled by user code, which in turn means you have to wake up all threads to make it work, because this is the only way to ensure that the correct thread will get woken at all.