1 files changed, 269 insertions, 0 deletions
diff --git a/src/main/async.c b/src/main/async.c
new file mode 100644
index 0000000..4e3fafc
--- /dev/null
+++ b/src/main/async.c
@@ -0,0 +1,269 @@
+#include "async.h"
+#include <stdlib.h>
+#include <pthread.h>
+
+struct thunk_result {
+    async_thunk_id_t id;
+    void* result;
+    struct thunk_result* next;
+};
+
+struct waiting_thunk {
+    async_thunk_id_t id;
+    async_thunk_t thunk;
+    void* args;
+    unsigned char awaitable;
+    struct waiting_thunk* next;
+};
+
+struct async_pool {
+    pthread_t* threads;
+    int n_threads;
+    bool joined;
+    bool destroyed;
+
+    struct waiting_thunk* queue_head;
+    struct waiting_thunk* queue_tail;
+    pthread_cond_t queue_cond;
+    async_thunk_id_t next_id;
+    pthread_mutex_t queue_lock;
+
+    pthread_cond_t result_cond;
+    struct thunk_result** thunk_results;
+    int result_buckets;
+    pthread_mutex_t result_lock;
+};
+
+static void store_result(async_pool_t* pool, async_thunk_id_t thunk_id, void* result) {
+    struct thunk_result* stored_result = malloc(sizeof(struct thunk_result));
+    if (stored_result == NULL) return;
+    stored_result->id = thunk_id;
+    stored_result->result = result;
+    stored_result->next = NULL;
+
+    unsigned int bucket = thunk_id % pool->result_buckets;
+    struct thunk_result* node = pool->thunk_results[bucket];
+    if (node == NULL) {
+        pool->thunk_results[bucket] = stored_result;
+        return;
+    }
+
+    while (node->next != NULL) node = node->next;
+    node->next = stored_result;
+}
+
+static void* thread_loop(void* args) {
+    async_pool_t* pool = (async_pool_t*) args;
+    pthread_mutex_lock(&pool->queue_lock);
+    while (!pool->destroyed) {
+        if (pool->queue_head == NULL) {
+            if (pool->joined) break;
+            pthread_cond_wait(&pool->queue_cond, &pool->queue_lock);
+            continue;
+        }
+
+        struct waiting_thunk* queue_item = pool->queue_head;
+        async_thunk_id_t thunk_id = queue_item->id;
+        async_thunk_t thunk = queue_item->thunk;
+        void* args = queue_item->args;
+        if (queue_item->next == NULL) {
+            pool->queue_head = NULL;
+            pool->queue_tail = NULL;
+        } else {
+            pool->queue_head = queue_item->next;
+        }
+        pthread_mutex_unlock(&pool->queue_lock);
+
+        bool awaitable = queue_item->awaitable;
+        free(queue_item);
+        void* result = thunk(args);
+
+        pthread_mutex_lock(&pool->result_lock);
+        if (awaitable) store_result(pool, thunk_id, result);
+        pthread_mutex_unlock(&pool->result_lock);
+        pthread_cond_broadcast(&pool->result_cond);
+
+        pthread_mutex_lock(&pool->queue_lock);
+    }
+    pthread_mutex_unlock(&pool->queue_lock);
+    return NULL;
+}
+
+static void abort_pool(async_pool_t* pool) {
+    pthread_mutex_destroy(&pool->queue_lock);
+    pthread_cond_destroy(&pool->queue_cond);
+    free(pool->threads);
+    free(pool);
+}
+
+async_pool_t* async_pool_create(int n_threads) {
+    if (n_threads < 1) return NULL;
+    async_pool_t* pool = malloc(sizeof(async_pool_t));
+    if (pool == NULL) return NULL;
+
+    pool->threads = malloc(sizeof(pthread_t) * n_threads);
+    if (pool->threads == NULL) {
+        free(pool);
+        return NULL;
+    }
+
+    pool->result_buckets = n_threads;
+    pool->thunk_results = calloc(pool->result_buckets, sizeof(struct thunk_result*));
+    if (pool->thunk_results == NULL) {
+        free(pool->threads);
+        free(pool);
+        return NULL;
+    }
+
+    pthread_cond_init(&pool->queue_cond, NULL);
+    pthread_cond_init(&pool->result_cond, NULL);
+    pthread_mutex_init(&pool->result_lock, NULL);
+    pthread_mutex_init(&pool->queue_lock, NULL);
+    if (pthread_mutex_lock(&pool->queue_lock) != 0) {
+        abort_pool(pool);
+        return NULL;
+    }
+
+    for (pool->n_threads = 0; pool->n_threads < n_threads; pool->n_threads++) {
+        if (pthread_create(&pool->threads[pool->n_threads], NULL, thread_loop, pool) != 0)
+            break;
+    }
+
+    pool->next_id = 1;
+    pool->queue_head = NULL;
+    pool->queue_tail = NULL;
+    pool->joined = false;
+    pool->destroyed = false;
+    if (pool->n_threads < 1 || pthread_mutex_unlock(&pool->queue_lock) != 0) {
+        pool->destroyed = true;
+        int i;
+        for (i = 0; i < pool->n_threads; i++) {
+            pthread_cancel(pool->threads[i]);
+        }
+        abort_pool(pool);
+        return NULL;
+    };
+    return pool;
+}
+
+static void destroy_queue(struct waiting_thunk* head) {
+    if (head == NULL) return;
+    destroy_queue(head->next);
+    free(head);
+}
+
+static void destroy_result(struct thunk_result* head) {
+    if (head == NULL) return;
+    destroy_result(head->next);
+    free(head);
+}
+
+async_thunk_id_t async_submit(async_pool_t* pool, async_thunk_t thunk, void* args, bool awaitable) {
+    struct waiting_thunk* item = malloc(sizeof(struct waiting_thunk));
+    if (item == NULL) return ASYNC_NO_THUNK;
+    item->thunk = thunk;
+    item->args = args;
+    item->awaitable = awaitable;
+    item->next = NULL;
+
+    pthread_mutex_lock(&pool->queue_lock);
+    if (pool->joined || pool->destroyed) {
+        pthread_mutex_unlock(&pool->queue_lock);
+        free(item);
+        return ASYNC_NO_THUNK;
+    }
+
+    item->id = pool->next_id++;
+    if (pool->queue_head == NULL) {
+        pool->queue_head = item;
+        pool->queue_tail = item;
+    } else {
+        pool->queue_tail->next = item;
+        pool->queue_tail = item;
+    }
+    pthread_mutex_unlock(&pool->queue_lock);
+    pthread_cond_signal(&pool->queue_cond);
+    return item->id;
+}
+
+static struct thunk_result* pop_result(async_pool_t* pool, async_thunk_id_t thunk_id) {
+    unsigned int bucket = thunk_id % pool->result_buckets;
+    struct thunk_result* node = pool->thunk_results[bucket];
+    if (node == NULL) return NULL;
+    if (node->id == thunk_id) {
+        pool->thunk_results[bucket] = node->next;
+        return node;
+    }
+    while (node->next != NULL) {
+        struct thunk_result* candidate = node->next;
+        if (candidate->id == thunk_id) {
+            node->next = candidate->next;
+            return candidate;
+        }
+        node = candidate;
+    }
+    return NULL;
+}
+
+void* async_await(async_pool_t* pool, async_thunk_id_t thunk_id) {
+    pthread_mutex_lock(&pool->result_lock);
+    while (!pool->destroyed) {
+        struct thunk_result* found = pop_result(pool, thunk_id);
+        if (found != NULL) {
+            pthread_mutex_unlock(&pool->result_lock);
+            void* result = found->result;
+            free(found);
+            return result;
+        }
+
+        pthread_cond_wait(&pool->result_cond, &pool->result_lock);
+    }
+    pthread_mutex_unlock(&pool->result_lock);
+    return NULL;
+}
+
+void async_pool_join(async_pool_t* pool) {
+    pthread_mutex_lock(&pool->queue_lock);
+    if (pool->joined) {
+        pthread_mutex_unlock(&pool->queue_lock);
+        return;
+    }
+    pool->joined = true;
+    pthread_cond_broadcast(&pool->queue_cond);
+    pthread_mutex_unlock(&pool->queue_lock);
+
+    int i;
+    for (i = 0; i < pool->n_threads; i++) {
+        pthread_join(pool->threads[i], NULL);
+    }
+    free(pool->threads);
+
+    pthread_cond_destroy(&pool->queue_cond);
+    destroy_queue(pool->queue_head);
+}
+
+void async_pool_destroy(async_pool_t* pool) {
+    async_pool_join(pool);
+
+    // the pattern lock / flag forbidden / broadcast / unlock / relock
+    // should place us last in the order of threads waiting for a lock,
+    // so we can safely destroy it
+    pthread_mutex_lock(&pool->queue_lock);
+    pthread_mutex_destroy(&pool->queue_lock);
+
+    pthread_mutex_lock(&pool->result_lock);
+    pool->destroyed = true;
+    pthread_cond_broadcast(&pool->result_cond);
+    pthread_mutex_unlock(&pool->result_lock);
+    pthread_mutex_lock(&pool->result_lock);
+    pthread_mutex_destroy(&pool->result_lock);
+    pthread_cond_destroy(&pool->result_cond);
+
+    int i;
+    for (i = 0; i < pool->result_buckets; i++) {
+        destroy_result(pool->thunk_results[i]);
+    }
+    free(pool->thunk_results);
+
+    free(pool);
+}