std::condition_variable checks the condition for the first time, or do you have to wait for someone to make a notify?

Question

std::condition_variable checks the condition for the first time, or do you have to wait for someone to make a notify?

Answer 1

This is answered by reading documentation .

It's like:

while (!pred()) {
    wait(lock);
}

So, the condition is checked first .

This can also be shown by testing it (though, to be fair, it's hard to know just from that whether the results are deterministic).