gistfile1.m

void __AllowOnceEvery(double seconds, void (^block)(void), NSTimeInterval * lastTime)
{
    NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
    if (now - *lastTime > seconds) {
        *lastTime = now;
        block();
    }
}


#define AllowOnceEvery(seconds, block) \
        do {\
            static NSTimeInterval lastTime = 0;\
            __AllowOnceEvery(seconds, block, &lastTime);\
        } while (0)



int main (int argc, const char * argv[])
{
    BOOL done = NO;
    
    // Do some long process
    do {
        @autoreleasepool {
            
            // Do some work
            done = work();
            
            // Send progress updates
            AllowOnceEvery(1.0, ^{
                printf("Progress: %f", progress);
            });
        }
        
    } while (!done);
    
    return 0;
}