Method unschedule

src/bthread/timer_thread.cpp:259–277

Notice that we don't recycle the Task in this function, let TimerThread::run do it. The side effect is that we may allocate many unscheduled tasks before TimerThread wakes up. The number is approximately qps * timeout_s. Under the precondition that ResourcePool caches 128K for each thread, with some further calculations, we can conclude that in a RPC scenario: when timeout / latency < 2730 (

// between timeout and latency in most RPC scenarios, this is why we don't
// try to reuse tasks right now inside unschedule() with more complicated code.
int TimerThread::unschedule(TaskId task_id) {
    const butil::ResourceId<Task> slot_id = slot_of_task_id(task_id);
    Task* const task = butil::address_resource(slot_id);
    if (task == NULL) {
        LOG(ERROR) << "Invalid task_id=" << task_id;
        return -1;
    }
    const uint32_t id_version = version_of_task_id(task_id);
    uint32_t expected_version = id_version;
    // This CAS is rarely contended, should be fast.
    // The acquire fence is paired with release fence in Task::run_and_delete
    // to make sure that we see all changes brought by fn(arg).
    if (task->version.compare_exchange_strong(
            expected_version, id_version + 2,
            butil::memory_order_acquire)) {
        return 0;
    }
    return (expected_version == id_version + 1) ? 1 : -1;
}

bool TimerThread::Task::run_and_delete() {
    const uint32_t id_version = version_of_task_id(task_id);