avutil: add thread executor

The executor design pattern was introduced by java
<https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/util/concurrent/Executor.html>
it also adapted by python
<https://docs.python.org/3/library/concurrent.futures.html>
Compared to handcrafted thread pool management, it greatly simplifies the thread code.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

1 files changed, 201 insertions, 0 deletions

diff --git a/libavutil/executor.c b/libavutil/executor.c
new file mode 100644
index 0000000000..0da919f4e8
--- /dev/null
+++ b/libavutil/executor.c
@@ -0,0 +1,201 @@
+/*
+ * Copyright (C) 2023 Nuo Mi
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+#include "internal.h"
+#include "mem.h"
+#include "thread.h"
+
+#include "executor.h"
+
+#if !HAVE_THREADS
+
+#define ExecutorThread  char
+
+#define executor_thread_create(t, a, s, ar)      0
+#define executor_thread_join(t, r)               do {} while(0)
+
+#else
+
+#define ExecutorThread  pthread_t
+
+#define executor_thread_create(t, a, s, ar)      pthread_create(t, a, s, ar)
+#define executor_thread_join(t, r)               pthread_join(t, r)
+
+#endif //!HAVE_THREADS
+
+typedef struct ThreadInfo {
+    AVExecutor *e;
+    ExecutorThread thread;
+} ThreadInfo;
+
+struct AVExecutor {
+    AVTaskCallbacks cb;
+    int thread_count;
+
+    ThreadInfo *threads;
+    uint8_t *local_contexts;
+
+    AVMutex lock;
+    AVCond cond;
+    int die;
+
+    AVTask *tasks;
+};
+
+static AVTask* remove_task(AVTask **prev, AVTask *t)
+{
+    *prev  = t->next;
+    t->next = NULL;
+    return t;
+}
+
+static void add_task(AVTask **prev, AVTask *t)
+{
+    t->next = *prev;
+    *prev   = t;
+}
+
+static int run_one_task(AVExecutor *e, void *lc)
+{
+    AVTaskCallbacks *cb = &e->cb;
+    AVTask **prev;
+
+    for (prev = &e->tasks; *prev && !cb->ready(*prev, cb->user_data); prev = &(*prev)->next)
+        /* nothing */;
+    if (*prev) {
+        AVTask *t = remove_task(prev, *prev);
+        ff_mutex_unlock(&e->lock);
+        cb->run(t, lc, cb->user_data);
+        ff_mutex_lock(&e->lock);
+        return 1;
+    }
+    return 0;
+}
+
+#if HAVE_THREADS
+static void *executor_worker_task(void *data)
+{
+    ThreadInfo *ti = (ThreadInfo*)data;
+    AVExecutor *e  = ti->e;
+    void *lc       = e->local_contexts + (ti - e->threads) * e->cb.local_context_size;
+
+    ff_mutex_lock(&e->lock);
+    while (1) {
+        if (e->die) break;
+
+        if (!run_one_task(e, lc)) {
+            //no task in one loop
+            ff_cond_wait(&e->cond, &e->lock);
+        }
+    }
+    ff_mutex_unlock(&e->lock);
+    return NULL;
+}
+#endif
+
+static void executor_free(AVExecutor *e, const int has_lock, const int has_cond)
+{
+    if (e->thread_count) {
+        //signal die
+        ff_mutex_lock(&e->lock);
+        e->die = 1;
+        ff_cond_broadcast(&e->cond);
+        ff_mutex_unlock(&e->lock);
+
+        for (int i = 0; i < e->thread_count; i++)
+            executor_thread_join(e->threads[i].thread, NULL);
+    }
+    if (has_cond)
+        ff_cond_destroy(&e->cond);
+    if (has_lock)
+        ff_mutex_destroy(&e->lock);
+
+    av_free(e->threads);
+    av_free(e->local_contexts);
+
+    av_free(e);
+}
+
+AVExecutor* av_executor_alloc(const AVTaskCallbacks *cb, int thread_count)
+{
+    AVExecutor *e;
+    int has_lock = 0, has_cond = 0;
+    if (!cb || !cb->user_data || !cb->ready || !cb->run || !cb->priority_higher)
+        return NULL;
+
+    e = av_mallocz(sizeof(*e));
+    if (!e)
+        return NULL;
+    e->cb = *cb;
+
+    e->local_contexts = av_calloc(thread_count, e->cb.local_context_size);
+    if (!e->local_contexts)
+        goto free_executor;
+
+    e->threads = av_calloc(thread_count, sizeof(*e->threads));
+    if (!e->threads)
+        goto free_executor;
+
+    has_lock = !ff_mutex_init(&e->lock, NULL);
+    has_cond = !ff_cond_init(&e->cond, NULL);
+
+    if (!has_lock || !has_cond)
+        goto free_executor;
+
+    for (/* nothing */; e->thread_count < thread_count; e->thread_count++) {
+        ThreadInfo *ti = e->threads + e->thread_count;
+        ti->e = e;
+        if (executor_thread_create(&ti->thread, NULL, executor_worker_task, ti))
+            goto free_executor;
+    }
+    return e;
+
+free_executor:
+    executor_free(e, has_lock, has_cond);
+    return NULL;
+}
+
+void av_executor_free(AVExecutor **executor)
+{
+    if (!executor || !*executor)
+        return;
+    executor_free(*executor, 1, 1);
+    *executor = NULL;
+}
+
+void av_executor_execute(AVExecutor *e, AVTask *t)
+{
+    AVTaskCallbacks *cb = &e->cb;
+    AVTask **prev;
+
+    ff_mutex_lock(&e->lock);
+    if (t) {
+        for (prev = &e->tasks; *prev && cb->priority_higher(*prev, t); prev = &(*prev)->next)
+            /* nothing */;
+        add_task(prev, t);
+    }
+    ff_cond_signal(&e->cond);
+    ff_mutex_unlock(&e->lock);
+
+#if !HAVE_THREADS
+    // We are running in a single-threaded environment, so we must handle all tasks ourselves
+    while (run_one_task(e, e->local_contexts))
+        /* nothing */;
+#endif
+}