parallel.c

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdatomic.h>
#include <threads.h>

#define NUM_THREADS 8

static _Atomic size_t tasks_reserved;
static _Atomic size_t tasks_complete;

static size_t tasks_count;

static void do_task(size_t t) {
	// ...
	printf("Boo! %zu\n", t);
}

static int task_thread(void* param) {
	while (true) {
		size_t t = tasks_reserved++;

		if (t >= tasks_count) {
			// we're done, just waiting on the tasks
			// on the other threads to be completed.
			// wait until it's completed
			while (tasks_complete < tasks_count) { 
				thrd_yield();
			}
			continue;
		}

		do_task(t);
		tasks_complete++;
	}

	return 0;
}

static void parallel_dispatch(size_t count) {
	tasks_count = count;
	tasks_complete = 0;
	tasks_reserved = 0;

	// lazy init some threads into existence
	static thrd_t threads[NUM_THREADS];
	static bool made_threads = false;

	if (!made_threads) {
		made_threads = true;
		for (int i = 0; i < NUM_THREADS; i++) {
			thrd_create(&threads[i], task_thread, NULL);
		}
	}

	// wait until it's completed
	while (tasks_complete < tasks_count) { 
		thrd_yield();
	}
}

int main() {
	parallel_dispatch(100);

	return 0;
}