Function remove_pthread_contention_site

src/bthread/mutex.cpp:605–624

template <typename Mutex>
inline bool remove_pthread_contention_site(const Mutex* mutex,
                                           bthread_contention_site_t* saved_csite) {
    MutexMapEntry& entry = g_mutex_map[hash_mutex_ptr(mutex) & (MUTEX_MAP_SIZE - 1)];
    butil::static_atomic<uint64_t>& m = entry.versioned_mutex;
    if ((m.load(butil::memory_order_relaxed) & ((((uint64_t)1) << PTR_BITS) - 1))
        != (uint64_t)mutex) {
        // This branch should be the most common case since most locks are
        // neither contended nor sampled. We have one memory indirection and
        // several bitwise operations here, the cost should be ~ 5-50ns
        return false;
    }
    // Although this branch is inside a contended lock, we should also make it
    // as simple as possible because altering the critical section too much
    // may make unpredictable impact to thread interleaving status, which
    // makes profiling result less accurate.
    *saved_csite = entry.csite;
    make_contention_site_invalid(&entry.csite);
    m.store(0, butil::memory_order_release);
    return true;
}

// Submit the contention along with the callsite('s stacktrace)
void submit_contention(const bthread_contention_site_t& csite, int64_t now_ns) {