Make something happen after 5 minutes has passed, while other code still runs in C++

问题

I am trying to make a timer, so after five minutes something happens. The catch is that while the timer is being checked constantly I need other code to be running. I have created a sample below, of how the actually code looks, the function with the timer is in class, so I did the same thing below. Here is the code:

This code assumes all necessary headers are included

Class.h:

class MyClass
{
public:
    void TimerFunc(int MSeconds);
};

void MyClass::TimerFunc(int MSeconds)
{
    Sleep(MSeconds); //Windows.h
    //Event code
    return;
}

Main.cpp:

int main()
{
    MyClass myClass;
    myClass.TimerFunc(300); //300 is 5 minutes

    //Here we do not want to wait for the five minutes to pass,
    //instead we want to continue the rest of the code and check
    //for user input as below
    std::cout << "This should print before the Event Code happens.";
}

The problem here is that the code waits for the five minutes to pass, and then continues. I'm not sure if threading would be a good option here, I haven't done much with it before, if anyone could help me with that, or knows a better way to go about it, any help is appreciated.

回答1:

If you don't mind your Event executing in a different thread-context, you could have your Timer class spawn a thread to do the waiting and then the event-execution; or (on POSIX OS's) set up a SIGALRM signal and have the signal handler do the Event. The downside of that is that if your event-code does anything non-trivial, you'll need to worry about race conditions with the concurrently executing main thread.

The other approach is to have your main thread check the clock every so often, and if the time-to-execute has passed, have your main thread call your Event routine at that time. That has the advantage of automatic thread-safety, but the disadvantage is that you'll have to add that code into your thread's main event loop; you can't easily hide it away inside a class like the one in your example.

回答2:

With C++11 threads, this would work like this:

int main()
{
    MyClass myClass;
    thread ti([](MyClass &m){m.TimerFunc(300); }, ref(myClass));   // create and launch thread 

    // ... code executed concurrently to threaded code

    ti.join();             // wait for the thread to end (or you'll crash !!)
}

Add a private member to your class:

     atomic<bool> run=true;   // designed to avoid race issue with concurrent access

Update its timer function to loop while this variable is true:

void MyClass::TimerFunc(int MSeconds)
{
    while (run) {
        this_thread::sleep_for(chrono::milliseconds(MSeconds));  // standard sleep instead of microsoft's one
        //Event code
    }
    return;
}

Foresee within the class a member function to stop the threaded loop:

void Stop() {
    run = false;
}

Finally update main() to call myClass.Stop() when the timer function is no longer needed (i.e. before calling ti.join() )

EDIT: attention, nasty error to avoid: be careful to refer to ref(myClass) in the thread constructor. If you would forget this, the thread ti would use a reference to a copy of myClass instead of the original object.

来源：https://stackoverflow.com/questions/26705710/make-something-happen-after-5-minutes-has-passed-while-other-code-still-runs-in

标签

c++

multithreading

class

timer