C++ Handbook

Header Reference: <condition_variable>

Header Reference: <condition_variable>

Condition variables and predicate-based blocking waits from <condition_variable>.

How to use this reference page

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Header Reference: <condition_variable>

Main facilities

What this header is for

Use <condition_variable> to block threads efficiently until shared state changes and a predicate becomes true.

Common patterns

Notes

Minimal example

#include <condition_variable>
#include <mutex>

int main() {
    std::mutex guard;
    std::condition_variable cv;
    bool ready = true;
    std::unique_lock lock(guard);
    cv.wait(lock, [&] { return ready; });
    return 0;
}

What to verify before relying on this header

  • How the code will shut down, unblock, or stop safely under cancellation and failure paths.
  • Which state is shared, which synchronization primitive owns that responsibility, and which memory-ordering assumptions are actually required.
  • Whether a higher-level facility such as `std::jthread`, `std::future`, or structured task composition would reduce coordination risk.