Re: [FFmpeg-devel] [PATCH v3] vvcdec: add thread executor

[Nuo Mi <nuomi2021@gmail.com>]

On Wed, Jul 19, 2023 at 9:13 PM Nuo Mi <nuomi2021@gmail.com> wrote:

> The executor design pattern was inroduced 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.
> ---
>  libavutil/Makefile   |   2 +
>  libavutil/executor.c | 201 +++++++++++++++++++++++++++++++++++++++++++
>  libavutil/executor.h |  67 +++++++++++++++
>  3 files changed, 270 insertions(+)
>  create mode 100644 libavutil/executor.c
>  create mode 100644 libavutil/executor.h
>
> diff --git a/libavutil/Makefile b/libavutil/Makefile
> index bd9c6f9e32..b40aacdd06 100644
> --- a/libavutil/Makefile
> +++ b/libavutil/Makefile
> @@ -31,6 +31,7 @@ HEADERS = adler32.h
>                \
>            encryption_info.h                                             \
>            error.h                                                       \
>            eval.h                                                        \
> +          executor.h                                                    \
>            fifo.h                                                        \
>            file.h                                                        \
>            frame.h                                                       \
> @@ -126,6 +127,7 @@ OBJS = adler32.o
>                   \
>         encryption_info.o                                                \
>         error.o                                                          \
>         eval.o                                                           \
> +       executor.o                                                       \
>         fifo.o                                                           \
>         file.o                                                           \
>         file_open.o                                                      \
> diff --git a/libavutil/executor.c b/libavutil/executor.c
> new file mode 100644
> index 0000000000..9823fc3d5d
> --- /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 pthread_create(t, a, s, ar)     0
> +#define pthread_join(t, r)              do {} while(0)
> +
> +#define pthread_cond_init(c, a)         0
> +#define pthread_cond_broadcast(c)       do {} while(0)
> +#define pthread_cond_signal(c)          do {} while(0)
> +#define pthread_cond_wait(c, m)         do {} while(0)
> +#define pthread_cond_destroy(c)         do {} while(0)
> +
> +#define pthread_mutex_init(m, a)        0
> +#define pthread_mutex_lock(l)           do {} while(0)
> +#define pthread_mutex_unlock(l)         do {} while(0)
> +#define pthread_mutex_destroy(l)        do {} while(0)
> +#endif
> +
> +typedef struct ThreadInfo {
> +    AVExecutor *e;
> +    pthread_t thread;
> +} ThreadInfo;
> +
> +struct AVExecutor {
> +    AVTaskCallbacks cb;
> +    int thread_count;
> +
> +    ThreadInfo *threads;
> +    uint8_t *local_contexts;
> +
> +    pthread_mutex_t lock;
> +    pthread_cond_t 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);
> +        pthread_mutex_unlock(&e->lock);
> +        cb->run(t, lc, cb->user_data);
> +        pthread_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;
> +
> +    pthread_mutex_lock(&e->lock);
> +    while (1) {
> +        if (e->die) break;
> +
> +        if (!run_one_task(e, lc)) {
> +            //no task in one loop
> +            pthread_cond_wait(&e->cond, &e->lock);
> +        }
> +    }
> +    pthread_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
> +        pthread_mutex_lock(&e->lock);
> +        e->die = 1;
> +        pthread_cond_broadcast(&e->cond);
> +        pthread_mutex_unlock(&e->lock);
> +
> +        for (int i = 0; i < e->thread_count; i++)
> +            pthread_join(e->threads[i].thread, NULL);
> +    }
> +    if (has_cond)
> +        pthread_cond_destroy(&e->cond);
> +    if (has_lock)
> +        pthread_mutex_destroy(&e->lock);
> +
> +    av_free(e->threads);
> +    av_free(e->local_contexts);
> +
> +    av_free(e);
> +}
> +
> +AVExecutor* avpriv_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_calloc(1, 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 = !pthread_mutex_init(&e->lock, NULL);
> +    has_cond = !pthread_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 (pthread_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 avpriv_executor_free(AVExecutor **executor)
> +{
> +    if (!executor || !*executor)
> +        return;
> +    executor_free(*executor, 1, 1);
> +    *executor = NULL;
> +}
> +
> +void avpriv_executor_execute(AVExecutor *e, AVTask *t)
> +{
> +    AVTaskCallbacks *cb = &e->cb;
> +    AVTask **prev;
> +
> +    pthread_mutex_lock(&e->lock);
> +    if (t) {
> +        for (prev = &e->tasks; *prev && cb->priority_higher(*prev, t);
> prev = &(*prev)->next)
> +            /* nothing */;
> +        add_task(prev, t);
> +    }
> +    pthread_cond_signal(&e->cond);
> +    pthread_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
> +}
> diff --git a/libavutil/executor.h b/libavutil/executor.h
> new file mode 100644
> index 0000000000..48c7d47c7d
> --- /dev/null
> +++ b/libavutil/executor.h
> @@ -0,0 +1,67 @@
> +/*
> + * 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
> + */
> +
> +#ifndef AVUTIL_EXECUTOR_H
> +#define AVUTIL_EXECUTOR_H
> +
> +typedef struct AVExecutor AVExecutor;
> +typedef struct AVTask AVTask;
> +
> +struct AVTask {
> +    AVTask *next;
> +};
> +
> +typedef struct AVTaskCallbacks {
> +    void *user_data;
> +
> +    int local_context_size;
> +
> +    // return 1 if a's priority > b's priority
> +    int (*priority_higher)(const AVTask *a, const AVTask *b);
> +
> +    // task is ready for run
> +    int (*ready)(const AVTask *t, void *user_data);
> +
> +    // run the task
> +    int (*run)(AVTask *t, void *local_context, void *user_data);
> +} AVTaskCallbacks;
> +
> +/**
> + * Alloc executor
> + * @param callbacks callback strucutre for executor
> + * @param thread_count worker thread number
> + * @return return the executor
> + */
> +AVExecutor* avpriv_executor_alloc(const AVTaskCallbacks *callbacks, int
> thread_count);
> +
> +/**
> + * Free executor
> + * @param e  pointer to executor
> + */
> +void avpriv_executor_free(AVExecutor **e);
> +
> +/**
> + * Add task to executor
> + * @param e pointer to executor
> + * @param t pointer to task. If NULL, it will wakeup one work thread
> + */
> +void avpriv_executor_execute(AVExecutor *e, AVTask *t);
> +
> +#endif //AVUTIL_EXECUTOR_H
> --
> 2.25.1
>
>
Changes since v2:
* move executor to avutil
* fix for --disable-pthreads
* remove duplicate free code in executor_alloc and executor_free

I also disabled the HAVE_THREADS macro in this file only for testing
purposes.
The executor is also functional in single-threaded environments.
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