Question

DBThread::DBThread() : running_(false)
{

}

DBThread::~DBThread()
{
    if (thread_)
    {
        thread_->join();
    }
}

void DBThread::Init()
{
    thread_ = std::make_shared<std::thread>(std::bind(&DBThread::Run, this));
    std::unique_lock<std::mutex> lock(mutex_);
    cv_.wait(lock, [&] {return running_; });
    std::cout << "Init success";
}

void DBThread::AddTask(std::shared_ptr<Delegate> task)
{
    std::lock_guard<std::mutex> lock(mutex_);
    task_queue_.push(task);
}

void DBThread::Run()
{
    running_ = true;
    cv_.notify_all();
    while (true)
    {
        std::unique_lock<std::mutex> lock(mutex_);
        cv_.wait(lock, [&] {return !task_queue_.empty(); });
        std::cout << "run task" << std::endl;
    }
}

我有两个线程，让我们把它命名为A和B，A调用Init并等待B完全初始化，即使running_为true，A有时会挂起等待。不知道为什么会发生这种情况。任何帮助都将受到赞赏。< / p>

Answer 1

std::condition_variable::wait(lock, pred)与

基本相同

while (!pred()) {
    wait(lock);
}

如果线程将running_设置为true并在检查谓词的时间之间调用notify_all()，但在调用wait之前，则通知将丢失，并且等待将等到另一个通知到来。最简单的解决方法是：

void DBThread::Run()
{
    std::unique_lock<std::mutex> lock(mutex_);
    running_ = true;
    cv_.notify_all();
    while (true)
    {
        cv_.wait(lock, [&] {return !task_queue_.empty(); });
        std::cout << "run task" << std::endl;
    }
}

notify_all不会唤醒等待线程

1 个答案: