1 files changed, 223 insertions, 0 deletions
diff --git a/misc/thread_pool.c b/misc/thread_pool.c
new file mode 100644
index 0000000..e20d9d0
--- /dev/null
+++ b/misc/thread_pool.c
@@ -0,0 +1,223 @@
+/* Copyright (C) 2018 the mpv developers
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "common/common.h"
+#include "osdep/threads.h"
+#include "osdep/timer.h"
+
+#include "thread_pool.h"
+
+// Threads destroy themselves after this many seconds, if there's no new work
+// and the thread count is above the configured minimum.
+#define DESTROY_TIMEOUT 10
+
+struct work {
+    void (*fn)(void *ctx);
+    void *fn_ctx;
+};
+
+struct mp_thread_pool {
+    int min_threads, max_threads;
+
+    mp_mutex lock;
+    mp_cond wakeup;
+
+    // --- the following fields are protected by lock
+
+    mp_thread *threads;
+    int num_threads;
+
+    // Number of threads which have taken up work and are still processing it.
+    int busy_threads;
+
+    bool terminate;
+
+    struct work *work;
+    int num_work;
+};
+
+static MP_THREAD_VOID worker_thread(void *arg)
+{
+    struct mp_thread_pool *pool = arg;
+
+    mp_thread_set_name("worker");
+
+    mp_mutex_lock(&pool->lock);
+
+    int64_t destroy_deadline = 0;
+    bool got_timeout = false;
+    while (1) {
+        struct work work = {0};
+        if (pool->num_work > 0) {
+            work = pool->work[pool->num_work - 1];
+            pool->num_work -= 1;
+        }
+
+        if (!work.fn) {
+            if (got_timeout || pool->terminate)
+                break;
+
+            if (pool->num_threads > pool->min_threads) {
+                if (!destroy_deadline)
+                    destroy_deadline = mp_time_ns() + MP_TIME_S_TO_NS(DESTROY_TIMEOUT);
+                if (mp_cond_timedwait_until(&pool->wakeup, &pool->lock, destroy_deadline))
+                    got_timeout = pool->num_threads > pool->min_threads;
+            } else {
+                mp_cond_wait(&pool->wakeup, &pool->lock);
+            }
+            continue;
+        }
+
+        pool->busy_threads += 1;
+        mp_mutex_unlock(&pool->lock);
+
+        work.fn(work.fn_ctx);
+
+        mp_mutex_lock(&pool->lock);
+        pool->busy_threads -= 1;
+
+        destroy_deadline = 0;
+        got_timeout = false;
+    }
+
+    // If no termination signal was given, it must mean we died because of a
+    // timeout, and nobody is waiting for us. We have to remove ourselves.
+    if (!pool->terminate) {
+        for (int n = 0; n < pool->num_threads; n++) {
+            if (mp_thread_id_equal(mp_thread_get_id(pool->threads[n]),
+                                   mp_thread_current_id()))
+            {
+                mp_thread_detach(pool->threads[n]);
+                MP_TARRAY_REMOVE_AT(pool->threads, pool->num_threads, n);
+                mp_mutex_unlock(&pool->lock);
+                MP_THREAD_RETURN();
+            }
+        }
+        MP_ASSERT_UNREACHABLE();
+    }
+
+    mp_mutex_unlock(&pool->lock);
+    MP_THREAD_RETURN();
+}
+
+static void thread_pool_dtor(void *ctx)
+{
+    struct mp_thread_pool *pool = ctx;
+
+
+    mp_mutex_lock(&pool->lock);
+
+    pool->terminate = true;
+    mp_cond_broadcast(&pool->wakeup);
+
+    mp_thread *threads = pool->threads;
+    int num_threads = pool->num_threads;
+
+    pool->threads = NULL;
+    pool->num_threads = 0;
+
+    mp_mutex_unlock(&pool->lock);
+
+    for (int n = 0; n < num_threads; n++)
+        mp_thread_join(threads[n]);
+
+    assert(pool->num_work == 0);
+    assert(pool->num_threads == 0);
+    mp_cond_destroy(&pool->wakeup);
+    mp_mutex_destroy(&pool->lock);
+}
+
+static bool add_thread(struct mp_thread_pool *pool)
+{
+    mp_thread thread;
+
+    if (mp_thread_create(&thread, worker_thread, pool) != 0)
+        return false;
+
+    MP_TARRAY_APPEND(pool, pool->threads, pool->num_threads, thread);
+    return true;
+}
+
+struct mp_thread_pool *mp_thread_pool_create(void *ta_parent, int init_threads,
+                                             int min_threads, int max_threads)
+{
+    assert(min_threads >= 0);
+    assert(init_threads <= min_threads);
+    assert(max_threads > 0 && max_threads >= min_threads);
+
+    struct mp_thread_pool *pool = talloc_zero(ta_parent, struct mp_thread_pool);
+    talloc_set_destructor(pool, thread_pool_dtor);
+
+    mp_mutex_init(&pool->lock);
+    mp_cond_init(&pool->wakeup);
+
+    pool->min_threads = min_threads;
+    pool->max_threads = max_threads;
+
+    mp_mutex_lock(&pool->lock);
+    for (int n = 0; n < init_threads; n++)
+        add_thread(pool);
+    bool ok = pool->num_threads >= init_threads;
+    mp_mutex_unlock(&pool->lock);
+
+    if (!ok)
+        TA_FREEP(&pool);
+
+    return pool;
+}
+
+static bool thread_pool_add(struct mp_thread_pool *pool, void (*fn)(void *ctx),
+                            void *fn_ctx, bool allow_queue)
+{
+    bool ok = true;
+
+    assert(fn);
+
+    mp_mutex_lock(&pool->lock);
+    struct work work = {fn, fn_ctx};
+
+    // If there are not enough threads to process all at once, but we can
+    // create a new thread, then do so. If work is queued quickly, it can
+    // happen that not all available threads have picked up work yet (up to
+    // num_threads - busy_threads threads), which has to be accounted for.
+    if (pool->busy_threads + pool->num_work + 1 > pool->num_threads &&
+        pool->num_threads < pool->max_threads)
+    {
+        if (!add_thread(pool)) {
+            // If we can queue it, it'll get done as long as there is 1 thread.
+            ok = allow_queue && pool->num_threads > 0;
+        }
+    }
+
+    if (ok) {
+        MP_TARRAY_INSERT_AT(pool, pool->work, pool->num_work, 0, work);
+        mp_cond_signal(&pool->wakeup);
+    }
+
+    mp_mutex_unlock(&pool->lock);
+    return ok;
+}
+
+bool mp_thread_pool_queue(struct mp_thread_pool *pool, void (*fn)(void *ctx),
+                          void *fn_ctx)
+{
+    return thread_pool_add(pool, fn, fn_ctx, true);
+}
+
+bool mp_thread_pool_run(struct mp_thread_pool *pool, void (*fn)(void *ctx),
+                        void *fn_ctx)
+{
+    return thread_pool_add(pool, fn, fn_ctx, false);
+}