# Processes

---

## Per Process Task Queue

## Asynchronous Task Queue

# Queuing

## Sync

## Async

# Running

# Example

```c
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <pthread.h>
#include <assert.h>

#define PROCESSES 12

#define I 5

#define FIB 30

typedef struct _task task;

typedef void task_fn(task *t);

#define TASK_STATE_SIZE 20

#define TASK_QUEUE_ASYNC -1

#define TASK_MAIN_PROCESS 0

typedef struct _task {
    _Atomic bool join_ready;
    int32_t worker_id;
    void *state[TASK_STATE_SIZE];
    void *return_value;
    struct _task *next, *join;
    task_fn *fn;
} task;

task *task_pool = NULL, *task_async_queue_head = NULL, *task_async_queue_tail = NULL;

_Atomic size_t task_async_queue_length = 0;

pthread_mutex_t task_pool_mutex = PTHREAD_MUTEX_INITIALIZER, task_async_queue_mutex = PTHREAD_MUTEX_INITIALIZER;

pthread_cond_t task_async_queue_cond = PTHREAD_COND_INITIALIZER;

void __attribute__((destructor)) task_destructor(void) {
    while (task_pool) {
        task *t = task_pool;
        task_pool = task_pool->next;
        free(t);
    }
    pthread_mutex_destroy(&task_pool_mutex);
    pthread_cond_destroy(&task_async_queue_cond);
    pthread_mutex_destroy(&task_async_queue_mutex);
}

typedef struct {
    task *head, *tail;
    pthread_t thread;
} process;

process worker[PROCESSES] = {};

task *task_init(task_fn fn) {
    task *t = NULL;
    pthread_mutex_lock(&task_pool_mutex);
    if (task_pool) {
        t = task_pool;
        task_pool = task_pool->next;
    }
    pthread_mutex_unlock(&task_pool_mutex);
    if (!t)
        t = malloc(sizeof(task));
    __atomic_clear(&t->join_ready, __ATOMIC_SEQ_CST);
    t->worker_id = TASK_QUEUE_ASYNC;
    for (ssize_t state_index = 0; state_index < TASK_STATE_SIZE; state_index++)
        t->state[state_index] = NULL;
    t->return_value = NULL;
    t->next = t->join = NULL;
    t->fn = fn;
    return t;
}

void task_free(task *t) {
    pthread_mutex_lock(&task_pool_mutex);
    t->next = task_pool;
    task_pool = t;
    pthread_mutex_unlock(&task_pool_mutex);
}

void task_queue_async(task *t) {
    pthread_mutex_lock(&task_async_queue_mutex);
    if (task_async_queue_tail)
        task_async_queue_tail = task_async_queue_tail->next = t;
    else
        task_async_queue_head = task_async_queue_tail = t;
    pthread_mutex_unlock(&task_async_queue_mutex);
    pthread_cond_signal(&task_async_queue_cond);
}

void task_queue_sync(task *t, int32_t worker_id) {
    if (worker_id == TASK_QUEUE_ASYNC)
        return task_queue_async(t);
    if (worker[worker_id].tail)
        worker[worker_id].tail = worker[worker_id].tail->next = t;
    else
        worker[worker_id].head = worker[worker_id].tail = t;
    return;
}

void task_ready_queue(task *t) {
    if (!__atomic_test_and_set(&t->join_ready, __ATOMIC_SEQ_CST) || !t->join)
        return;
    task *join = t->join;
    t->join = NULL;
    __atomic_clear(&t->join_ready, __ATOMIC_SEQ_CST);
    task_queue_sync(join, join->worker_id == t->worker_id ? t->worker_id : TASK_QUEUE_ASYNC);
}

void task_join(task *restrict t, task *restrict join, task_fn fn) {
    join->fn = fn;
    t->join = join;
    task_ready_queue(t);
}

void task_done(task *t) {
    task_ready_queue(t);
}

_Atomic size_t running = PROCESSES;

void *task_loop(void *arg) {
    int32_t worker_id = (intptr_t) arg;
    for (;;) {
        task *t = NULL;
        if (worker[worker_id].head) {
            t = worker[worker_id].head;
            if (worker[worker_id].head != worker[worker_id].tail)
                worker[worker_id].head = worker[worker_id].head->next;
            else
                worker[worker_id].head = worker[worker_id].tail = NULL;
        } else {
            pthread_mutex_lock(&task_async_queue_mutex);
            if (task_async_queue_head) {
                t = task_async_queue_head;
                if (task_async_queue_head != task_async_queue_tail)
                    task_async_queue_head = task_async_queue_head->next;
                else
                    task_async_queue_head = task_async_queue_tail = NULL;
            }
            pthread_mutex_unlock(&task_async_queue_mutex);
        }
        if (t) {
            t->next = NULL;
            t->worker_id = worker_id;
            t->fn(t);
            continue;
        }
        running--;
        if (!running) {
            for (intptr_t worker_id = 1; worker_id < PROCESSES; worker_id++)
                pthread_cond_signal(&task_async_queue_cond);
            break;
        }
        pthread_mutex_lock(&task_async_queue_mutex);
        pthread_cond_wait(&task_async_queue_cond, &task_async_queue_mutex);
        pthread_mutex_unlock(&task_async_queue_mutex);
        if (!running)
            break;
        running++;
    }
    return NULL;
}

void task_run(void) {
    for (intptr_t worker_id = 1; worker_id < PROCESSES; worker_id++)
        pthread_create(&worker[worker_id].thread, NULL, task_loop, (void*) worker_id);
    task_loop(0);
    for (intptr_t worker_id = 1; worker_id < PROCESSES; worker_id++)
        pthread_join(worker[worker_id].thread, NULL);
}

/*
fib : Fn[n] $ (
    ? {
        n <= 0 { 0 }
        n < 2 { 1 }
        { + (fib `call n - 1; fib `call n - 2) }
    }
    v : Vector[`fork_type fib] $ ()
    @ 1 .. I { v `push fib `fork FIB }
    @ v {[fib_task] `print "fib(%) = %\n" `format (FIB; `join fib_task) }
    `print "Complete\n"
)
*/

#define LOG printf("%d: %s\n", t->worker_id, __FUNCTION__)

_Atomic size_t counter = 0;

/*
    0: i
    1: arg
    2: child_a
    3: child_b
*/

void fib_c(task *t) {
    task *child_a = t->state[2], *child_b = t->state[3];
    t->return_value = (void*) ((intptr_t) child_a->return_value + (intptr_t) child_b->return_value);
    task_free(child_a);
    task_free(child_b);
    task_done(t);
}

void fib_a(task *t);

void fib_b(task *t) {
    intptr_t arg = (intptr_t) t->state[1];
    task *child_b = t->state[3] = task_init(fib_a);
    child_b->state[1] = (void*) (arg - 2);
    task_queue_sync(child_b, t->worker_id);
    task_join(child_b, t, fib_c);
}

void fib_a(task *t) {
    intptr_t arg = (intptr_t) t->state[1];
    if (arg <= 0) {
       t->return_value = (void*) 0;
       task_done(t);
       return;
    }
    if (arg < 2) {
        t->return_value = (void*) 1;
        task_done(t);
        return;
    }
    task *child_a = t->state[2] = task_init(fib_a);
    child_a->state[1] = (void*) (arg - 1);
    task_queue_sync(child_a, t->worker_id);
    task_join(child_a, t, fib_b);
}

intptr_t fib(intptr_t n) {
    if (n <= 0)
        return 0;
    if (n < 2)
        return 1;
    return fib(n - 1) + fib(n - 2);
}

void fib_rec(task *t) {
    intptr_t arg = (intptr_t) t->state[1];
    printf("fib thread: %d\n", t->worker_id);
    t->return_value = (void*) fib(arg);
    task_done(t);
}

void start_b(task *t) {
    counter++;
    task *f = t->state[(intptr_t) t->state[0]];
    intptr_t i = (intptr_t) f->state[0], arg = (intptr_t) f->state[1], ret = (intptr_t) f->return_value;
    printf("i: %ld, fib(%ld) = %ld\n", i + 1, arg, ret);
    task_free(f);
    t->state[0]++;
    if ((intptr_t) t->state[0] == I + 1) {
        printf("Complete\n");
        task_done(t);
        task_free(t);
        return;
    }
    task_join(t->state[(intptr_t) t->state[0]], t, start_b);
}

void start_a(task *t) {
    t->state[0] = (void*) 1;
    for (intptr_t i = 0; i < I; i++) {
        //task *f = task_init(fib_a);
        task *f = task_init(fib_rec);
        f->state[0] = (void*) i;
        f->state[1] = (void*) FIB;
        t->state[i + 1] = f;
        task_queue_async(f);
    }
    task_join(t->state[(intptr_t) t->state[0]], t, start_b);
}

int main(void) {
    task *t = task_init(start_a);
    task_queue_sync(t, TASK_MAIN_PROCESS);
    task_run();
    assert(counter == I);
    return 0;
}
```