#include <sys/mman.h>  // mmap()
#include <unistd.h>    // fork()
#include <sys/wait.h>  // wait()
#include <semaphore.h> // sem_init(), Link with -pthread
#include <errno.h>     // errno
#include <stdint.h>    // uint32_t
#include <stdio.h>     // printf()

int do_fork1();
int do_fork2();
int parent();
int worker_gl();
int worker_sdl();

typedef struct {
	sem_t worker_gl_can_render, worker_sdl_can_render, parent_can_read_result;
	int scene;
	uint32_t framebuf[256*256];
} shm_t;

shm_t *shm;

int main() {
	shm = mmap(NULL, sizeof(shm_t), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, 0, 0);
	if (sem_init(&shm->worker_gl_can_render, 1, 0) < 0) return 1;
	if (sem_init(&shm->worker_sdl_can_render, 1, 0) < 0) return 2;
	if (sem_init(&shm->parent_can_read_result, 1, 0) < 0) return 3;
	shm->scene = 0;
	return do_fork1();
}

int do_fork1() {
	switch (fork()) {
		case -1: return 4; break;
		case 0:  return worker_gl(); break;
		default: return do_fork2(); break;
	}
}

int do_fork2() {
	switch (fork()) {
		case -1: return 5; break;
		case 0:  return worker_sdl(); break;
		default: return parent(); break;
	}
}

int parent() {
	int i, child_status;

	shm->scene++;
	printf("parent1 %i\n", shm->scene);


	for(i=0;i<4;i++) {
		if ( sem_post(&shm->worker_sdl_can_render) == -1 ) {
			return 6;
		}

		while ( sem_wait(&shm->parent_can_read_result) == -1 ) {
			switch(errno) {
				case EINTR:
				case EAGAIN:
					break;
				default:
					return 7;
			}
		}
		printf("parent2 %i\n", shm->scene);

		if ( sem_post(&shm->worker_gl_can_render) == -1 ) {
			return 6;
		}

		while ( sem_wait(&shm->parent_can_read_result) == -1 ) {
			switch(errno) {
				case EINTR:
				case EAGAIN:
					break;
				default:
					return 8;
			}
		}
		printf("parent3 %i\n", shm->scene);
	}

	if ( wait(&child_status) != -1 ) {
		if ( child_status > 0 ) return child_status;
	}
	if ( wait(&child_status) != -1 ) {
		if ( child_status > 0 ) return child_status;
	}
	return 0;
}

int worker_gl() {
	int done=0;
	while ( !done ) {
		while ( sem_wait(&shm->worker_gl_can_render) == -1 ) {
			switch(errno) {
				case EINTR:
				case EAGAIN:
					break;
				default:
					return 10;
			}
		}
		printf("worker_gl %i\n", shm->scene);
		
		shm->scene++;

		if ( sem_post(&shm->parent_can_read_result) == -1 ) {
			return 11;
		}
	}
	return 0;
}

int worker_sdl() {
	int done=0;
	while ( !done ) {
		while ( sem_wait(&shm->worker_sdl_can_render) == -1 ) {
			switch(errno) {
				case EINTR:
				case EAGAIN:
					break;
				default:
					return 20;
			}
		}

		printf("worker_sdl %i\n", shm->scene);
		shm->scene++;

		if ( sem_post(&shm->parent_can_read_result) == -1 ) {
			return 21;
		}
	}
	return 0;
}