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Commit db419383 authored by Igor Murashkin's avatar Igor Murashkin
Browse files

libutils: Clarify Condition::signal wakes up exactly one thread 

Contrary to POSIX pthread_cond_signal guarantees, bionic will wake up
either zero or one threads.

Change-Id: I628fcd4d5bd8d5290104506f86caa82c54142230
parent cf805481

include/utils/Condition.h

+12 −1
Original line number Diff line number Diff line
@@ -60,7 +60,7 @@ public: 
    status_t wait(Mutex& mutex);

    // same with relative timeout

    status_t waitRelative(Mutex& mutex, nsecs_t reltime);

    // Signal the condition variable, allowing one thread to continue.

    // Signal the condition variable, allowing exactly one thread to continue.

    void signal();

    // Signal the condition variable, allowing one or all threads to continue.

    void signal(WakeUpType type) {
@@ -132,6 +132,17 @@ inline status_t Condition::waitRelative(Mutex& mutex, nsecs_t reltime) { 
#endif // HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE

}

inline void Condition::signal() {

    /*

     * POSIX says pthread_cond_signal wakes up "one or more" waiting threads.

     * However bionic follows the glibc guarantee which wakes up "exactly one"

     * waiting thread.

     *

     * man 3 pthread_cond_signal

     *   pthread_cond_signal restarts one of the threads that are waiting on

     *   the condition variable cond. If no threads are waiting on cond,

     *   nothing happens. If several threads are waiting on cond, exactly one

     *   is restarted, but it is not specified which.

     */

    pthread_cond_signal(&mCond);

}

inline void Condition::broadcast() {