Method in C++ to call a function every certain number of minutes

Question

I'm using Visual Studio 2012 and C++, I need to call a function every 5 minutes, I've managed to do it but it consumes 25% of my CPU which is far from ideal.

The code is as follows,

time_t start;
time_t end;
time(&start);
while (1) {
time(&end);
double dif = difftime (end,start);
if (dif >= 300) { autofunction(); time(&start);} else {} }

Is there a more CPU efficient way to go about calling a function every 5 minutes or any way to slow down my while loop?

Any guidance will be greatly appreciated.

I should of probably mentioned that I don't want to use sleep because I want to do other things at the same time. — Ryan, Dec 23 '12 at 21:12
@user1661022 in the else part of your if statement you do those other things? — wimh, Dec 23 '12 at 21:13
"25% cpu" doesn't mean all that much these days. You probably mean, it uses 100% of 1 of my 4 cpu's, or "it takes all cpu time it gets", or something like that — stijn, Dec 23 '12 at 21:13
How about setting a timer via `SetTimer()` and then handling the WM_TIMER message? — user987280, Dec 23 '12 at 21:16
What kind of application is it? You can create second thread and let it sleep — makc, Dec 23 '12 at 21:18

score 2 · Accepted Answer · answered Dec 23 '12 at 21:19

2

Windows has Sleep(), and for something that happens every 300 seconds, that's perfectly good. There are also timers in Windows, which potentially takes a timerproc argument, which is a function - but note that this is a C function, not C++, so it mustn't be a class member function unless it is a static one.

answered Dec 23 '12 at 21:19

Mats Petersson

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Umm, I think it's perfectly fine to pass a lambda or `std::bind` there. – Bartek Banachewicz Dec 23 '12 at 21:47
Yes, as long as it's not a member function, anything that is "directly callable as a function" should work just fine. I didn't want to write an essay on ALL of the restrictions and tricks with callback functions, but at least mention that it exists. – Mats Petersson Dec 23 '12 at 21:49

score 1 · Answer 2 · answered Dec 23 '12 at 21:46

1

Since nobody suggested that, you can just spawn a new std::thread and Sleep in it.

answered Dec 23 '12 at 21:46

Bartek Banachewicz

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Olaf Dietsche · Answer 3 · 2012-12-23T21:59:34.627

0

What you do is busy waiting. You constantly check for the time being elapsed and so use up the CPU time.

Since you're on windows, Using Timer Queues might be of interest.

This creates a timer with a callback function. You can do other work, while waiting for the timer to expire.

edited Dec 23 '12 at 21:59

answered Dec 23 '12 at 21:42

Olaf Dietsche

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score 0 · Answer 4 · answered Dec 23 '12 at 22:08

I think the best answer will depend on some more of the details of what you're doing. If you only need it to be approximately 5 minutes, maybe you can put the duration-elapsed calculation at a more programmatically convenient location, and you'll run the task the first time after 5 minutes when you check.

Otherwise, it seems like @BartekBanachewicz has the best suggestion of starting a thread, which uses sleep---without blocking your main thread doing whatever you're doing. As long as your main thread will definitely be running longer than 5 minutes, it shouldn't be a problem to always re-join() the thread at the end, or whenever.

Using thread's has the benefit of not requiring any windows specific stuff -- e.g. @OlafDietsche's suggestion, whatever Timer Queues are. With c++0x, threads are super-easy to use, see: http://en.cppreference.com/w/cpp/thread/thread; http://www.justsoftwaresolutions.co.uk/threading/multithreading-in-c++0x-part-1-starting-threads.html

Method in C++ to call a function every certain number of minutes

4 Answers4