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Technical Q&A QA1160

Preventing sleep

Q: How can I prevent system sleep while my application is running?

A: Most applications should not prevent system sleep, however, there are exceptions. For example, if your application is playing a long movie or slideshow, the user will probably get annoyed if the computer keeps going to sleep. Your application can prevent system sleep by calling UpdateSystemActivity once every 30 seconds. The following code shows how to create a CFRunLoopTimer that calls UpdateSystemActivity every 30 seconds.

Listing 1 Example usage of UpdateSystemActivity.

#include <CoreServices/CoreServices.h>

void

MyTimerCallback(CFRunLoopTimerRef timer, void *info)

    UpdateSystemActivity(OverallAct);

int

main (int argc, const char * argv[])

    CFRunLoopTimerRef timer;

    CFRunLoopTimerContext context = { 0, NULL, NULL, NULL, NULL };

    timer = CFRunLoopTimerCreate(NULL, CFAbsoluteTimeGetCurrent(), 30, 0, 0, MyTimerCallback, &context);

    if (timer != NULL); {

        CFRunLoopAddTimer(CFRunLoopGetCurrent(), timer, kCFRunLoopCommonModes);

    /* Start the run loop to receive timer callbacks. You don't need to

    call this if you already have a Carbon or Cocoa EventLoop running. */

    CFRunLoopRun();

    CFRunLoopTimerInvalidate(timer);

    CFRelease(timer);

    return (0);

Document Revision History

Date	Notes
2018-06-04	Moved to Retired Documents Library.
2004-10-22	Explains how your application can prevent the system from sleeping.
	Explains how your application can prevent the system from sleeping.