Function add_pthread_contention_site

src/bthread/mutex.cpp:586–602

template <typename Mutex>
inline bthread_contention_site_t*
add_pthread_contention_site(const Mutex* mutex) {
    MutexMapEntry& entry = g_mutex_map[hash_mutex_ptr(mutex) & (MUTEX_MAP_SIZE - 1)];
    butil::static_atomic<uint64_t>& m = entry.versioned_mutex;
    uint64_t expected = m.load(butil::memory_order_relaxed);
    // If the entry is not used or used by previous profiler, try to CAS it.
    if (expected == 0 ||
        (expected >> PTR_BITS) != (g_cp_version & ((1 << (64 - PTR_BITS)) - 1))) {
        uint64_t desired = (g_cp_version << PTR_BITS) | (uint64_t)mutex;
        if (m.compare_exchange_strong(
                expected, desired, butil::memory_order_acquire)) {
            return &entry.csite;
        }
    }
    g_nconflicthash.fetch_add(1, butil::memory_order_relaxed);
    return NULL;
}

template <typename Mutex>
inline bool remove_pthread_contention_site(const Mutex* mutex,