Re: [FFmpeg-devel] [PATCH v2 01/27] avcodec/threadprogress: Add new API for frame-threaded progress

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> The API is similar to the ThreadFrame API, with the exception
> that it no longer has an included AVFrame and that it has its
> own mutexes and condition variables which makes it more independent
> of pthread_frame.c. One can wait on anything via a ThreadProgress.
> One just has to ensure that the lifetime of the object containing
> the ThreadProgress is long enough. This will typically be solved
> by putting a ThreadProgress in a refcounted structure that is
> shared between threads.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
> Now including its own mutex and condition variable. Hopefully
> no system has constraints on the number of mutexes and condition
> variables it supports.
> 
>  libavcodec/threadprogress.c | 73 +++++++++++++++++++++++++++++
>  libavcodec/threadprogress.h | 91 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 164 insertions(+)
>  create mode 100644 libavcodec/threadprogress.c
>  create mode 100644 libavcodec/threadprogress.h
> 
> diff --git a/libavcodec/threadprogress.c b/libavcodec/threadprogress.c
> new file mode 100644
> index 0000000000..dd2a4d2336
> --- /dev/null
> +++ b/libavcodec/threadprogress.c
> @@ -0,0 +1,73 @@
> +/*
> + * Copyright (c) 2022 Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> + *
> + * 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 <limits.h>
> +#include <stdatomic.h>
> +
> +#include "pthread_internal.h"
> +#include "threadprogress.h"
> +#include "libavutil/attributes.h"
> +
> +DEFINE_OFFSET_ARRAY(ThreadProgress, thread_progress, init,
> +                    (offsetof(ThreadProgress, progress_mutex)),
> +                    (offsetof(ThreadProgress, progress_cond)));
> +
> +av_cold int ff_thread_progress_init(ThreadProgress *pro, int init_mode)
> +{
> +    atomic_init(&pro->progress, init_mode ? -1 : INT_MAX);
> +    if (!init_mode) {
> +        pro->init = 0;
> +        return 0;
> +    }
> +    return ff_pthread_init(pro, thread_progress_offsets);
> +}
> +
> +av_cold void ff_thread_progress_destroy(ThreadProgress *pro)
> +{
> +    ff_pthread_free(pro, thread_progress_offsets);
> +}
> +
> +void ff_thread_progress_report(ThreadProgress *pro, int n)
> +{
> +    if (atomic_load_explicit(&pro->progress, memory_order_relaxed) >= n)
> +        return;
> +
> +    atomic_store_explicit(&pro->progress, n, memory_order_release);
> +
> +    pthread_mutex_lock(&pro->progress_mutex);
> +    pthread_cond_broadcast(&pro->progress_cond);
> +    pthread_mutex_unlock(&pro->progress_mutex);
> +}
> +
> +void ff_thread_progress_await(const ThreadProgress *pro_c, int n)
> +{
> +    /* Casting const away here is safe, because we only read from progress
> +     * and will leave pro_c in the same state upon leaving the function
> +     * as it had at the beginning. */
> +    ThreadProgress *pro = (ThreadProgress*)pro_c;
> +
> +    if (atomic_load_explicit(&pro->progress, memory_order_acquire) >= n)
> +        return;
> +
> +    pthread_mutex_lock(&pro->progress_mutex);
> +    while (atomic_load_explicit(&pro->progress, memory_order_relaxed) < n)
> +        pthread_cond_wait(&pro->progress_cond, &pro->progress_mutex);
> +    pthread_mutex_unlock(&pro->progress_mutex);
> +}
> diff --git a/libavcodec/threadprogress.h b/libavcodec/threadprogress.h
> new file mode 100644
> index 0000000000..786802cbf1
> --- /dev/null
> +++ b/libavcodec/threadprogress.h
> @@ -0,0 +1,91 @@
> +/*
> + * Copyright (c) 2022 Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> + *
> + * 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 AVCODEC_THREADPROGRESS_H
> +#define AVCODEC_THREADPROGRESS_H
> +
> +/**
> + * ThreadProgress is an API to easily notify other threads about progress
> + * of any kind as long as it can be packaged into an int and is consistent
> + * with the natural ordering of integers.
> + *
> + * Each initialized ThreadProgress can be in one of two modes: No-op mode
> + * or ordinary mode. In the former mode, ff_thread_report_progress() and
> + * ff_thread_await_progress() are no-ops to simply support usecases like
> + * non-frame-threading. Only in the latter case perform these functions
> + * what their name already implies.
> + */
> +
> +#include <limits.h>
> +#include <stdatomic.h>
> +#include "libavutil/thread.h"
> +
> +/**
> + * This struct should be treated as opaque by users.
> + */
> +typedef struct ThreadProgress {
> +    atomic_int progress;
> +    unsigned   init;
> +    AVMutex progress_mutex;
> +    AVCond  progress_cond;
> +} ThreadProgress;
> +
> +/**
> + * Initialize a ThreadProgress.
> + *
> + * @param init_mode If zero, the ThreadProgress will be initialized so that
> + *                  to be in no-op mode as described above. Otherwise
> + */
> +int ff_thread_progress_init(ThreadProgress *pro, int init_mode);
> +
> +/**
> + * Destroy a ThreadProgress. Can be called on a ThreadProgress that
> + * has never been initialized provided that the ThreadProgress struct
> + * has been initially zeroed. Must be called even if ff_thread_progress_init()
> + * failed.
> + */
> +void ff_thread_progress_destroy(ThreadProgress *pro);
> +
> +/**
> + * Reset the ThreadProgress's progress progress counter; must only be called
> + * if it is not in use in any way (e.g. no thread may wait on it via
> + * ff_thread_progress_await()).
> + */
> +static inline void ff_thread_progress_reset(ThreadProgress *pro)
> +{
> +    atomic_init(&pro->progress, pro->init ? -1 : INT_MAX);
> +}
> +
> +/**
> + * This function is a no-op in no-op mode; otherwise it notifies
> + * other threads that a certain level of progress has been reached.
> + * Later calls with lower values of progress have no effect.
> + */
> +void ff_thread_progress_report(ThreadProgress *pro, int progress);
> +
> +/**
> + * This function is a no-op in no-op mode; otherwise it waits
> + * until other threads have reached a certain level of progress:
> + * This function will return after another thread has called
> + * ff_thread_progress_report() with the same or higher value for progress.
> + */
> +void ff_thread_progress_await(const ThreadProgress *pro, int progress);
> +
> +#endif /* AVCODEC_THREADPROGRESS_H */

Will apply this patchset tomorrow unless there are objections.

- Andreas

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