Prevent sleep on Mac

preventsleep.c

#import <IOKit/pwr_mgt/IOPMLib.h>

// build with:
// clang -framework IOKit -framework Foundation preventsleep.c -o preventsleep

int main(int argc, char** argv) {
    // kIOPMAssertionTypeNoDisplaySleep prevents display sleep,
    // kIOPMAssertionTypeNoIdleSleep prevents idle sleep

    // reasonForActivity is a descriptive string used by the system whenever it needs 
    // to tell the user why the system is not sleeping. For example, 
    // "Mail Compacting Mailboxes" would be a useful string.

    // NOTE: IOPMAssertionCreateWithName limits the string to 128 characters. 
    CFStringRef reasonForActivity= CFSTR("Describe Activity Type");

    IOPMAssertionID assertionID;
    IOReturn success = IOPMAssertionCreateWithName(
        kIOPMAssertionTypeNoDisplaySleep, 
        kIOPMAssertionLevelOn,
        reasonForActivity,
        &assertionID
    );
    
    if (success == kIOReturnSuccess) {
        // The system is prevented from sleeping here.
        sleep(3 * 60 * 60);

        success = IOPMAssertionRelease(assertionID);
        // The system will be able to sleep again. 
    }
}