max-concurrent.c

#import <stdio.h>
#import <dispatch/dispatch.h>
#import <libkern/OSAtomic.h>
#import <unistd.h>

/*
gcc-4.2 -arch x86_64 -std=gnu99 -O0 -mdynamic-no-pic -Wall -Werror -isysroot /Developer/SDKs/MacOSX10.6.sdk -mmacosx-version-min=10.6 -gdwarf-2 max-concurrent.c -o max-concurrent
*/

int main(int argc, char *argv[])
{
	static int32_t CurrentRunning = 0;
	
	dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
	for (int32_t i = 0; i < 100; i++) {
		dispatch_async(queue, ^{
			int32_t running = OSAtomicIncrement32(&CurrentRunning);
			fprintf(stderr, "running %d\n", running);
			while (1)
				sleep(1) // without the sleep (just a spin loop), only #core ops will be started.  with it, the full batch will start.
				;
		});
	}
	
	dispatch_main();
	return 0;
}