Use of usleep to idle a thread and avoid full CPU core use.

idle_test.c

#include <stdio.h>
#ifdef IDLE
#include <unistd.h>
#endif

int main () {
        int a = 0, b = 0, sum = 0;
        while (1) {
                sum = a + b;
#ifdef IDLE
                usleep(1000);
#endif
        }
}

Makefile

all: idle-on idle-off

idle-on:
	${CC} -DIDLE idle_test.c -o idle-on

idle-off:
	${CC} idle_test.c -o idle-off

clean:
	rm -f *.o idle-on idle-off