Hi,

In my demo, I create 3 threads, the first and the second thread are wait for the global pthread_cond with different pthread_mutex, the last thread will call pthread_cond_broadcast. 

When I build without musl, the output like this:

task 3 pthread_cond_broadcast end time 0.000054

task 2 pthread_cond_wait end time 0.000566

task 1 pthread_cond_wait end time 0.000612

task 2 pthread_cond_broadcast end time 1.012233

task 1 pthread_cond_broadcast end time 1.012247

But when I build with static lib of musl(libc.a) and run , the output like this:

task 3 pthread_cond_broadcast end time 0.000026

task 1 pthread_cond_wait end time 0.000074

task 1 pthread_cond_broadcast end time 1.013168

task 2 pthread_cond_wait end time 1.013245

task 2 pthread_cond_broadcast end time 2.022992

it seems that the second wakeup thead is waiting until the first wakeup thead unlock the mutex(different mute in the two threads).

musl version : 1.2.4

pthread_cond_t g_cond = PTHREAD_COND_INITIALIZER;

pthread_mutex_t g_mutex1 = PTHREAD_MUTEX_INITIALIZER;

pthread_mutex_t g_mutex2 = PTHREAD_MUTEX_INITIALIZER;

auto tStart = std::chrono::steady_clock::now();

void* ThreadTaskOne(void* arg)

{

    pthread_mutex_lock(&g_mutex1);

    pthread_cond_wait(&g_cond, &g_mutex1);

    auto tEnd = std::chrono::steady_clock::now();

    auto diff = std::chrono::duration<double>(tEnd - tStart);

    printf("task 1 pthread_cond_wait end time %f\n", diff.count());

    sleep(1);

    pthread_mutex_unlock(&g_mutex1);

    tEnd = std::chrono::steady_clock::now();

    diff = std::chrono::duration<double>(tEnd - tStart);

    printf("task 1 pthread_cond_broadcast end time %f\n", diff.count());

    return nullptr;

}

void* ThreadTaskTwo(void* arg)

{

    pthread_mutex_lock(&g_mutex2);

    pthread_cond_wait(&g_cond, &g_mutex2);

    auto tEnd = std::chrono::steady_clock::now();

    auto diff = std::chrono::duration<double>(tEnd - tStart);

    printf("task 2 pthread_cond_wait end time %f\n", diff.count());

    sleep(1);

    pthread_mutex_unlock(&g_mutex2);

    tEnd = std::chrono::steady_clock::now();

    diff = std::chrono::duration<double>(tEnd - tStart);

    printf("task 2 pthread_cond_broadcast end time %f\n", diff.count());

    return nullptr;

}

void* BroadcastNotifyMutex(void* arg)

{

    tStart = std::chrono::steady_clock::now();

    pthread_cond_broadcast(&g_cond);

    auto tEnd = std::chrono::steady_clock::now();

    auto diff = std::chrono::duration<double>(tEnd - tStart);

    printf("task 3 pthread_cond_broadcast end time %lf\n", diff.count());

    return nullptr;

}

int main()

{

    pthread_t threadOne, threadTwo, threadThree;

    pthread_create(&threadOne, nullptr, ThreadTaskOne, nullptr);

    pthread_create(&threadTwo, nullptr, ThreadTaskTwo, nullptr);

    sleep(3);

    pthread_create(&threadThree, nullptr, BroadcastNotifyMutex, nullptr);

    pthread_join(threadOne, nullptr);

    pthread_join(threadTwo, nullptr);

    pthread_join(threadThree, nullptr);

    return 0;

}