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mirror of https://github.com/mpv-player/mpv synced 2024-12-22 23:02:37 +00:00
mpv/misc/dispatch.c
wm4 4395a4f837 player: don't enter playloop for client API requests
This _actually_ does what commit 8716c2e8 promised, and gives a slight
performance improvement for client API users which make a lot of
requests (like reading properties).

The main issue was that mp_dispatch_lock() (which client.c uses to get
exclusive access to the core) still called the wakeup callback, which
made mp_dispatch_queue_process() exit. So the playloop got executed
again, and since it does a lot of stuff, performance could be reduced.
2016-09-16 20:24:52 +02:00

337 lines
13 KiB
C

/*
* This file is part of mpv.
*
* mpv 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.
*
* mpv 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 mpv. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdbool.h>
#include <assert.h>
#include "common/common.h"
#include "osdep/threads.h"
#include "osdep/timer.h"
#include "dispatch.h"
struct mp_dispatch_queue {
struct mp_dispatch_item *head, *tail;
pthread_mutex_t lock;
pthread_cond_t cond;
void (*wakeup_fn)(void *wakeup_ctx);
void *wakeup_ctx;
// Make mp_dispatch_queue_process() exit if it's idle.
bool interrupted;
// The target thread is blocked by mp_dispatch_queue_process(). Note that
// mp_dispatch_lock() can set this from true to false to keep the thread
// blocked (this stops if from processing other dispatch items, and from
// other threads to return from mp_dispatch_lock(), making it an exclusive
// lock).
bool idling;
// A mp_dispatch_lock() call is requesting an exclusive lock.
bool lock_request;
// Used to block out threads calling mp_dispatch_queue_process() while
// they're externall locked via mp_dispatch_lock().
// We could use a simple counter (increment it instead of adding a frame,
// also increment it when locking), but with this we can perform some
// minimal debug checks.
struct lock_frame *frame;
};
struct lock_frame {
struct lock_frame *prev;
pthread_t thread;
pthread_t locked_thread;
bool locked;
};
struct mp_dispatch_item {
mp_dispatch_fn fn;
void *fn_data;
bool asynchronous;
bool completed;
struct mp_dispatch_item *next;
};
static void queue_dtor(void *p)
{
struct mp_dispatch_queue *queue = p;
assert(!queue->head);
assert(!queue->idling);
assert(!queue->lock_request);
assert(!queue->frame);
pthread_cond_destroy(&queue->cond);
pthread_mutex_destroy(&queue->lock);
}
// A dispatch queue lets other threads run callbacks in a target thread.
// The target thread is the thread which calls mp_dispatch_queue_process().
// Free the dispatch queue with talloc_free(). At the time of destruction,
// the queue must be empty. The easiest way to guarantee this is to
// terminate all potential senders, then call mp_dispatch_run() with a
// function that e.g. makes the target thread exit, then pthread_join() the
// target thread, and finally destroy the queue. Another way is calling
// mp_dispatch_queue_process() after terminating all potential senders, and
// then destroying the queue.
struct mp_dispatch_queue *mp_dispatch_create(void *ta_parent)
{
struct mp_dispatch_queue *queue = talloc_ptrtype(ta_parent, queue);
*queue = (struct mp_dispatch_queue){0};
talloc_set_destructor(queue, queue_dtor);
pthread_mutex_init(&queue->lock, NULL);
pthread_cond_init(&queue->cond, NULL);
return queue;
}
// Set a custom function that should be called to guarantee that the target
// thread wakes up. This is intended for use with code that needs to block
// on non-pthread primitives, such as e.g. select(). In the case of select(),
// the wakeup_fn could for example write a byte into a "wakeup" pipe in order
// to unblock the select(). The wakeup_fn is called from the dispatch queue
// when there are new dispatch items, and the target thread should then enter
// mp_dispatch_queue_process() as soon as possible. Note that wakeup_fn is
// called under no lock, so you might have to do synchronization yourself.
void mp_dispatch_set_wakeup_fn(struct mp_dispatch_queue *queue,
void (*wakeup_fn)(void *wakeup_ctx),
void *wakeup_ctx)
{
queue->wakeup_fn = wakeup_fn;
queue->wakeup_ctx = wakeup_ctx;
}
static void mp_dispatch_append(struct mp_dispatch_queue *queue,
struct mp_dispatch_item *item)
{
pthread_mutex_lock(&queue->lock);
if (queue->tail) {
queue->tail->next = item;
} else {
queue->head = item;
}
queue->tail = item;
// Wake up the main thread; note that other threads might wait on this
// condition for reasons, so broadcast the condition.
pthread_cond_broadcast(&queue->cond);
// No wakeup callback -> assume mp_dispatch_queue_process() needs to be
// interrupted instead.
if (!queue->wakeup_fn)
queue->interrupted = true;
pthread_mutex_unlock(&queue->lock);
if (queue->wakeup_fn)
queue->wakeup_fn(queue->wakeup_ctx);
}
// Enqueue a callback to run it on the target thread asynchronously. The target
// thread will run fn(fn_data) as soon as it enter mp_dispatch_queue_process.
// Note that mp_dispatch_enqueue() will usually return long before that happens.
// It's up to the user to signal completion of the callback. It's also up to
// the user to guarantee that the context fn_data has correct lifetime, i.e.
// lives until the callback is run, and is freed after that.
void mp_dispatch_enqueue(struct mp_dispatch_queue *queue,
mp_dispatch_fn fn, void *fn_data)
{
struct mp_dispatch_item *item = talloc_ptrtype(NULL, item);
*item = (struct mp_dispatch_item){
.fn = fn,
.fn_data = fn_data,
.asynchronous = true,
};
mp_dispatch_append(queue, item);
}
// Like mp_dispatch_enqueue(), but the queue code will call talloc_free(fn_data)
// after the fn callback has been run. (The callback could trivially do that
// itself, but it makes it easier to implement synchronous and asynchronous
// requests with the same callback implementation.)
void mp_dispatch_enqueue_autofree(struct mp_dispatch_queue *queue,
mp_dispatch_fn fn, void *fn_data)
{
struct mp_dispatch_item *item = talloc_ptrtype(NULL, item);
*item = (struct mp_dispatch_item){
.fn = fn,
.fn_data = talloc_steal(item, fn_data),
.asynchronous = true,
};
mp_dispatch_append(queue, item);
}
// Run fn(fn_data) on the target thread synchronously. This function enqueues
// the callback and waits until the target thread is done doing this.
// This is redundant to calling the function inside mp_dispatch_[un]lock(),
// but can be helpful with code that relies on TLS (such as OpenGL).
void mp_dispatch_run(struct mp_dispatch_queue *queue,
mp_dispatch_fn fn, void *fn_data)
{
struct mp_dispatch_item item = {
.fn = fn,
.fn_data = fn_data,
};
mp_dispatch_append(queue, &item);
pthread_mutex_lock(&queue->lock);
while (!item.completed)
pthread_cond_wait(&queue->cond, &queue->lock);
pthread_mutex_unlock(&queue->lock);
}
// Process any outstanding dispatch items in the queue. This also handles
// suspending or locking the this thread from another thread via
// mp_dispatch_lock().
// The timeout specifies the minimum wait time. The actual time spent in this
// function can be much higher if the suspending/locking functions are used, or
// if executing the dispatch items takes time. On the other hand, this function
// can return much earlier than the timeout due to sporadic wakeups.
// Note that this will strictly return only after:
// - timeout has passed,
// - all queue items were processed,
// - the possibly acquired lock has been released
// It's possible to cancel the timeout by calling mp_dispatch_interrupt().
void mp_dispatch_queue_process(struct mp_dispatch_queue *queue, double timeout)
{
int64_t wait = timeout > 0 ? mp_add_timeout(mp_time_us(), timeout) : 0;
struct lock_frame frame = {
.thread = pthread_self(),
};
pthread_mutex_lock(&queue->lock);
frame.prev = queue->frame;
queue->frame = &frame;
// Logically, the queue is idling if the target thread is blocked in
// mp_dispatch_queue_process() doing nothing, so it's not possible to call
// it again. (Reentrant calls via callbacks temporarily reset the field.)
assert(!queue->idling);
queue->idling = true;
// Wake up thread which called mp_dispatch_lock().
if (queue->lock_request)
pthread_cond_broadcast(&queue->cond);
while (1) {
if (queue->lock_request || queue->frame != &frame || frame.locked) {
// Block due to something having called mp_dispatch_lock(). This
// is either a lock "acquire" (lock_request=true), or a lock in
// progress, with the possibility the thread which called
// mp_dispatch_lock() is now calling mp_dispatch_queue_process()
// (the latter means we must ignore any queue state changes,
// until it has been unlocked again).
pthread_cond_wait(&queue->cond, &queue->lock);
if (queue->frame == &frame && !frame.locked)
assert(queue->idling);
} else if (queue->head) {
struct mp_dispatch_item *item = queue->head;
queue->head = item->next;
if (!queue->head)
queue->tail = NULL;
item->next = NULL;
// Unlock, because we want to allow other threads to queue items
// while the dispatch item is processed.
// At the same time, we must prevent other threads from returning
// from mp_dispatch_lock(), which is done by idling=false.
queue->idling = false;
pthread_mutex_unlock(&queue->lock);
item->fn(item->fn_data);
pthread_mutex_lock(&queue->lock);
assert(!queue->idling);
queue->idling = true;
// Wakeup mp_dispatch_run(), also mp_dispatch_lock().
pthread_cond_broadcast(&queue->cond);
if (item->asynchronous) {
talloc_free(item);
} else {
item->completed = true;
}
} else if (wait > 0 && !queue->interrupted) {
struct timespec ts = mp_time_us_to_timespec(wait);
if (pthread_cond_timedwait(&queue->cond, &queue->lock, &ts))
wait = 0;
} else {
break;
}
}
queue->idling = false;
assert(!frame.locked);
assert(queue->frame == &frame);
queue->frame = frame.prev;
queue->interrupted = false;
pthread_mutex_unlock(&queue->lock);
}
// If the queue is inside of mp_dispatch_queue_process(), make it return as
// soon as all work items have been run, without waiting for the timeout. This
// does not make it return early if it's blocked by a mp_dispatch_lock().
// If mp_dispatch_queue_process() is called in a reentrant way (including the
// case where another thread calls mp_dispatch_lock() and then
// mp_dispatch_queue_process()), this affects only the "topmost" invocation.
void mp_dispatch_interrupt(struct mp_dispatch_queue *queue)
{
pthread_mutex_lock(&queue->lock);
queue->interrupted = true;
pthread_cond_broadcast(&queue->cond);
pthread_mutex_unlock(&queue->lock);
}
// Grant exclusive access to the target thread's state. While this is active,
// no other thread can return from mp_dispatch_lock() (i.e. it behaves like
// a pthread mutex), and no other thread can get dispatch items completed.
// Other threads can still queue asynchronous dispatch items without waiting,
// and the mutex behavior applies to this function only.
void mp_dispatch_lock(struct mp_dispatch_queue *queue)
{
pthread_mutex_lock(&queue->lock);
// First grab the queue lock. Something else could be holding the lock.
while (queue->lock_request)
pthread_cond_wait(&queue->cond, &queue->lock);
queue->lock_request = true;
// And now wait until the target thread gets "trapped" within the
// mp_dispatch_queue_process() call, which will mean we get exclusive
// access to the target's thread state.
while (!queue->idling) {
pthread_mutex_unlock(&queue->lock);
if (queue->wakeup_fn)
queue->wakeup_fn(queue->wakeup_ctx);
pthread_mutex_lock(&queue->lock);
if (queue->idling)
break;
pthread_cond_wait(&queue->cond, &queue->lock);
}
assert(queue->lock_request);
assert(queue->frame); // must be set if idling
assert(!queue->frame->locked); // no recursive locking on the same level
// "Lock".
queue->frame->locked = true;
queue->frame->locked_thread = pthread_self();
// Reset state for recursive mp_dispatch_queue_process() calls.
queue->lock_request = false;
queue->idling = false;
pthread_mutex_unlock(&queue->lock);
}
// Undo mp_dispatch_lock().
void mp_dispatch_unlock(struct mp_dispatch_queue *queue)
{
pthread_mutex_lock(&queue->lock);
// Must be called atfer a mp_dispatch_lock().
assert(queue->frame);
assert(queue->frame->locked);
assert(pthread_equal(queue->frame->locked_thread, pthread_self()));
// "Unlock".
queue->frame->locked = false;
// This must have been set to false during locking (except temporarily
// during recursive mp_dispatch_queue_process() calls).
assert(!queue->idling);
queue->idling = true;
// Wakeup mp_dispatch_queue_process(), and maybe other mp_dispatch_lock()s.
pthread_cond_broadcast(&queue->cond);
pthread_mutex_unlock(&queue->lock);
}