Function batch_waker

test/bthread_futex_unittest.cpp:167–190

} 

void* batch_waker(void* lock) {
    bthread_usleep(10000);
    const size_t REP = 100000;
    int nwakeup = 0;
    butil::Timer tm;
    tm.start();
    for (size_t i = 0; i < REP; ++i) {
        if (nevent.fetch_add(1, butil::memory_order_relaxed) == 0) {
            nwakeup += bthread::futex_wake_private(lock, 1);
            int expected = 1;
            while (1) {
                int last_expected = expected;
                if (nevent.compare_exchange_strong(expected, 0, butil::memory_order_relaxed)) {
                    break;
                }
                nwakeup += bthread::futex_wake_private(lock, expected - last_expected);
            }
        }
    }
    tm.stop();
    EXPECT_EQ(0, nwakeup);
    printf("futex_wake nop = %" PRId64 "ns\n", tm.n_elapsed() / REP);
    return NULL;
} 

TEST(FutexTest, many_futex_wake_nop_perf) {
    pthread_t th[8];