Function rwlock_unrdlock

src/bthread/rwlock.cpp:103–146

}

static inline int rwlock_unrdlock(bthread_rwlock_t* rwlock) {
    int reader_count = ((butil::atomic<int>*)&rwlock->reader_count)
        ->fetch_add(-1, butil::memory_order_relaxed) - 1;
    // Fast path.
    if (reader_count >= 0) {
        return 0;
    }
    // Slow path.

    if (BAIDU_UNLIKELY(reader_count + 1 == 0 || reader_count + 1 == -RWLockMaxReaders)) {
        CHECK(false) << "rwlock_unrdlock of unlocked rwlock";
        return EINVAL;
    }

    // A writer is pending.
    int reader_wait = ((butil::atomic<int>*)&rwlock->reader_wait)
        ->fetch_add(-1, butil::memory_order_relaxed) - 1;
    if (reader_wait != 0) {
        return 0;
    }

    // The last reader unblocks the writer.

    if (NULL == bthread::g_cp) {
        bthread_sem_post(&rwlock->writer_sema);
        return 0;
    }
    // Ask Collector if this (contended) locking should be sampled.
    const size_t sampling_range = bvar::is_collectable(&bthread::g_cp_sl);
    if (!sampling_range) { // Don't sample
        bthread_sem_post(&rwlock->writer_sema);
        return 0;
    }

    // Sampling.
    const int64_t start_ns = butil::cpuwide_time_ns();
    bthread_sem_post(&rwlock->writer_sema);
    const int64_t end_ns = butil::cpuwide_time_ns();
    const bthread_contention_site_t csite{end_ns - start_ns, sampling_range};
    // Submit `csite' for each reader immediately after
    // releasing rdlock to avoid the contention of `csite'.
    bthread::submit_contention(csite, end_ns);
    return 0;
}

#define DO_CSITE_IF_NEED                                                              \
    do {                                                                              \