c++ - condition_variable 项不计算为采用 0 个参数的函数

Question

我在将 wait 与我的 condition_variable 和函数一起使用时遇到问题。我希望我的 main 等待，直到我的池线程完成所有任务，然后再继续执行该程序。我想使用 std::condition_variable 和 isFinished() 池函数来让 main 等待。这是我所做的:

//above are tasks being queued in the thread pool
{
    std::unique_lock<std::mutex> lock(mainMut);
    waitMain.wait(lock, pool.isFinished());
}
//I need to make sure the threads are done with calculations before moving on

和我的pool.isFinished()

//definition in ThreadPool class
bool isFinished();

//implementation
bool ThreadPool::isFinished()
{
    {//aquire lock
        std::unique_lock<std::mutex>
            lock(queue_mutex);
        if(tasks.empty())
            return true;
        else
            return false;
    }//free lock
}

但我只是得到错误

C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\condition_variable(66): error C2064: term does not evaluate to a function taking 0 arguments
1>          main.cpp(243) : see reference to function template instantiation 'void std::condition_variable::wait<bool>(std::unique_lock<_Mutex> &,_Predicate)' being compiled
1>          with
1>          [
1>              _Mutex=std::mutex,
1>              _Predicate=bool
1>          ]

Answer 1

pool.isFinished() 被评估并返回一个 bool，但是 condition_variable::wait 需要一个可以重复调用的仿函数确定何时停止等待。您可以使用 std::bind 执行此操作:

waitMain.wait(lock, std::bind(&ThreadPool::isFinished, &pool));

或 lambda:

waitMain.wait(lock, [&]{ return pool.isFinished(); });