townengine/src/twn_workers.c

#include "twn_util.h"
#include "twn_workers_c.h"
#include "rendering/twn_draw_c.h"

SDL_sem *workers_job_semaphore;

static size_t workers_pool_size;
static SDL_mutex *workers_mutex;
static bool workers_should_exit;
static SDL_sem *workers_exit_semaphore; /* should come to count of `workers_pool_size` */

/* logic is such that when job is posted, worker threads attempt to grab it from any possible entry point */
/* if it did something, which is signaled by `true` return, go back to waiting on semaphore, so that it's decremented properly */
static int worker_thread(void *udata) {
    (void)udata;

    while (true) {
        /* check whether loop should end */
        SDL_LockMutex(workers_mutex);
        if (workers_should_exit) {
            SDL_UnlockMutex(workers_mutex);
            break;
        }
        SDL_UnlockMutex(workers_mutex);

        /* wait and occasionally go back to check whether it all should end */
        if (SDL_SemWaitTimeout(workers_job_semaphore, 100) == SDL_MUTEX_TIMEDOUT)
            continue;

        /* process models, which will trigger texture loads  */
        if (models_load_workers_thread())
            continue;

        if (textures_load_workers_thread())
            continue;
    }

    /* let the main thread collect it */
    SDL_SemPost(workers_exit_semaphore);

    return 0;
}


/* TODO: have a path for platforms without thread support? */
/* TODO: limit stack size? */
bool workers_init(size_t worker_count) {
    SDL_assert(workers_pool_size == 0);

    if (worker_count > MAX_WORKERS)
        worker_count = MAX_WORKERS;

    /* spawn a bunch of detached threads without references to them */
    for (size_t i = 0; i < worker_count; ++i) {
        SDL_Thread *thread = SDL_CreateThread(worker_thread, "worker", NULL);
        SDL_assert_always(thread);
        SDL_DetachThread(thread);
    }

    workers_pool_size = worker_count;
    workers_job_semaphore = SDL_CreateSemaphore(0);
    workers_exit_semaphore = SDL_CreateSemaphore(0);
    workers_mutex = SDL_CreateMutex();
    return true;
}


void workers_deinit(void) {
    SDL_LockMutex(workers_mutex);
    workers_should_exit = true;
    SDL_UnlockMutex(workers_mutex);

    for (size_t i = 0; i < workers_pool_size; ++i) {
        SDL_SemWait(workers_exit_semaphore);
    }

    SDL_DestroyMutex(workers_mutex);
    SDL_DestroySemaphore(workers_job_semaphore);
    SDL_DestroySemaphore(workers_exit_semaphore);
    workers_pool_size = 0;
}