Re: [FFmpeg-devel] [PATCH v4] vvcdec: add thread executor

[James Almer <jamrial@gmail.com>]

On 8/18/2023 1:17 PM, James Almer wrote:
> On 8/15/2023 11:50 AM, Nuo Mi 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 7828c94dc5..4711f8cde8 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                                                       \
>> @@ -127,6 +128,7 @@ 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..6b47ba0bf2
>> --- /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)
> 
> You have ff_mutex_* and AVMutex for this. I sent a patch adding 
> ff_cond_* and AVCond, as well as ff_thread_create/join and AVThread to 
> thread.h to simplify things.
> 
>> +#endif
>> +
>> +typedef struct ThreadInfo {
>> +    AVExecutor *e;
>> +    pthread_t thread;
> 
> You will need to use AVThread, else this will not be defined when 
> !HAVE_THREADS.

I ultimately didn't add AVThread, so you'll have to wrap this field. and 
the calls to pthread_create() and pthread_join().

> 
>> +} ThreadInfo;
>> +
>> +struct AVExecutor {
>> +    AVTaskCallbacks cb;
>> +    int thread_count;
>> +
>> +    ThreadInfo *threads;
>> +    uint8_t *local_contexts;
>> +
>> +    pthread_mutex_t lock;
>> +    pthread_cond_t cond;
> 
> Same here. AVMutex and AVCond.
> 
>> +    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* 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_calloc(1, sizeof(*e));
> 
> av_mallocz()
> 
>> +    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))

executor_worker_task() doesn't exist if !HAVE_THREADS, so like i said 
above, wrap this for loop.

>> +            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;
>> +
>> +    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..c3fe44bd0e
>> --- /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* av_executor_alloc(const AVTaskCallbacks *callbacks, int 
>> thread_count);
>> +
>> +/**
>> + * Free executor
>> + * @param e  pointer to executor
>> + */
>> +void av_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 av_executor_execute(AVExecutor *e, AVTask *t);
>> +
>> +#endif //AVUTIL_EXECUTOR_H
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