Massive CPU load using std::lock (c++11)

Question

My recent efforts to implement a thread/ mutex manager ended up in an 75% CPU load (4 core), while all four running threads were either in sleep or waiting for a mutex beein

Answer 1

First I want to thank for all answers.

During the work on an example code, that reproduces the effect, I found the source of trouble.

The conditional part locks both mutexes, while it uses just one for the std::condition_variable::wait() function.

But I still wonder, what going on behind the scene, that produces such a high CPU load.