Difference between revisions of "cpp/thread/notify all at thread exit"

Revision as of 17:42, 19 April 2012

Template:cpp/thread/sidebar

Transfers the ownership of the supplied, previously acquired, lock lk to internal storage and sets up the execution environment so when the current thread exits, after the destructors for all objects with thread-local storage duration are called, the condition variable is notified as in by

lk.unlock();
cond.notify_all();

The purpose of this function is to provide a mechanism to determine when all thread_local objects in a detached thread have been destructed. Equivalent effect may be achieved with the facilities provided by std::promise or std::packaged_task.

Notes

Calling this function if lock.mutex() is not locked by the current thread is undefined behavior.

Calling this function if lock.mutex() is not the same mutex as the one used by all other threads that are currently waiting on the same condition variable is undefined behavior.

The supplied lock lk is held until the thread exits. Once this function has been called, no more threads may acquire the same lock in order to wait on cond. If some thread is waiting on this condition variable, it should not attempt to release and reacquire the lock when it wakes up spuriously.

In typical use cases, this function is the last thing called by a detached thread.

Parameters

Return value

(none)

Example

#include <mutex>
#include <thread>
 
std::mutex m;
std::condition_variable cv;
 
bool ready = false;
ComplexType result;
 
void thread_func()
{
    std::unique_lock<std::mutex> lk(m);
    result = function_that_uses_thread_locals();
    ready = true;
    std::notify_all_at_thread_exit(cv, std::move(lk));
} // destroy thread_locals, notify cv, unlock mutex
 
int main()
{
    std::thread t(thread_func);
    t.detach();
    // do other work
    std::unique_lock<std::mutex> lk(m);
    while(!ready) {
        cv.wait(lk); // wait for the detached thread
    }
    process(result); // result is ready and thread_locals are destructed
}

See also