What's the difference between notify_all() and notify_one() of std::condition_variable?

c++ multithreading c++11 condition-variable
Yun Huang picture Yun Huang · Jan 26, 2012 · Viewed 24.1k times · Source

Currently, I am implementing a multi-thread project using std::thread in C++11. I use std::condition_variable to synchronize threads. In detail, one consumer function calls wait() member function of std::condition_variable to wait for task from a global task queue, another producer function generates and puts tasks into the queue. But I do not know the difference between notify_all() and notify_one() member functions of std::condition_variable. Which function should I use in the producer function? Thanks!

Answer

GManNickG picture GManNickG · Jan 26, 2012

If there are ten threads blocked on the condition variable, for example, notify_one() will unblock only one thread, while notify_all() will unblock them all. In your case, you'll want to use notify_one() so you don't wake up threads that don't have any work waiting for them.

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