mirror of
https://github.com/mpv-player/mpv
synced 2024-12-26 17:12:36 +00:00
9ccbc03ab1
When passing a very large timeout to mpthread_cond_timed_wait(), the calculations could overflow, setting tv_sec to a negative value, and making the pthread_cond_timed_wait() call return immediately. This accidentally made Lua support poll and burn CPU for no reason. The existing overflow check was ineffective on 32 bit systems. tv_sec is usually a long, so adding INT_MAX to it will usually not overflow on 64 bit systems, but on 32 bit systems it's guaranteed to overflow. Simply fix by clamping against a relatively high value. This will work until 1 week before the UNIX time wraps around in 32 bits.
310 lines
11 KiB
C
310 lines
11 KiB
C
/*
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* This file is part of mpv.
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*
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* mpv is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* mpv is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with mpv. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <time.h>
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#include <unistd.h>
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#include <sys/time.h>
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#include <limits.h>
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#include <assert.h>
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#include "common/common.h"
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#include "threads.h"
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static void get_pthread_time(struct timespec *out_ts)
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{
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#if defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0
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clock_gettime(CLOCK_REALTIME, out_ts);
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#else
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// OSX
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struct timeval tv;
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gettimeofday(&tv, NULL);
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out_ts->tv_sec = tv.tv_sec;
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out_ts->tv_nsec = tv.tv_usec * 1000UL;
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#endif
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}
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static void timespec_add_seconds(struct timespec *ts, double seconds)
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{
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// clamp to 1 week to avoid tv_sec overflows
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seconds = MPMIN(seconds, 60 * 60 * 24 * 7);
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unsigned long secs = (int)seconds;
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unsigned long nsecs = (seconds - secs) * 1000000000UL;
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if (nsecs + ts->tv_nsec >= 1000000000UL) {
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secs += 1;
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nsecs -= 1000000000UL;
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}
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ts->tv_sec += secs;
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ts->tv_nsec += nsecs;
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}
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// Return the argument to pass to e.g. pthread_cond_timedwait().
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// (Note that pthread_cond_t supports multiple clocks; this function computes
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// the time value needed by the default clock.)
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struct timespec mpthread_get_deadline(double timeout)
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{
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struct timespec ts;
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get_pthread_time(&ts);
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timespec_add_seconds(&ts, timeout);
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return ts;
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}
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// Call pthread_cond_timedwait() with a relative timeout in seconds
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int mpthread_cond_timed_wait(pthread_cond_t *cond, pthread_mutex_t *mutex,
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double timeout)
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{
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struct timespec ts = mpthread_get_deadline(timeout);
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return pthread_cond_timedwait(cond, mutex, &ts);
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}
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// Helper to reduce boiler plate.
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int mpthread_mutex_init_recursive(pthread_mutex_t *mutex)
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{
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pthread_mutexattr_t attr;
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pthread_mutexattr_init(&attr);
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pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
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int r = pthread_mutex_init(mutex, &attr);
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pthread_mutexattr_destroy(&attr);
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return r;
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}
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struct mp_dispatch_queue {
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struct mp_dispatch_item *head, *tail;
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pthread_mutex_t lock;
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pthread_cond_t cond;
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int suspend_requested;
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bool suspended;
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bool locked;
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void (*wakeup_fn)(void *wakeup_ctx);
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void *wakeup_ctx;
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};
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struct mp_dispatch_item {
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mp_dispatch_fn fn;
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void *fn_data;
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bool asynchronous;
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bool completed;
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struct mp_dispatch_item *next;
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};
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static void queue_dtor(void *p)
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{
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struct mp_dispatch_queue *queue = p;
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assert(!queue->head);
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assert(!queue->suspend_requested);
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assert(!queue->suspended);
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assert(!queue->locked);
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pthread_cond_destroy(&queue->cond);
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pthread_mutex_destroy(&queue->lock);
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}
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// A dispatch queue lets other threads runs callbacks in s target thread.
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// The target thread is the thread which created the queue and which calls
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// mp_dispatch_queue_process().
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// Free the dispatch queue with talloc_free(). (It must be empty.)
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struct mp_dispatch_queue *mp_dispatch_create(void *talloc_parent)
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{
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struct mp_dispatch_queue *queue = talloc_ptrtype(talloc_parent, queue);
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*queue = (struct mp_dispatch_queue){0};
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talloc_set_destructor(queue, queue_dtor);
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pthread_mutex_init(&queue->lock, NULL);
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pthread_cond_init(&queue->cond, NULL);
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return queue;
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}
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// Set a custom function that should be called to guarantee that the target
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// thread wakes up. This is intended for use with code that needs to block
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// on non-pthread primitives, such as e.g. select(). In the case of select(),
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// the wakeup_fn could for example write a byte into a "wakeup" pipe in order
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// to unblock the select(). The wakeup_fn is called from the dispatch queue
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// when there are new dispatch items, and the target thread should then enter
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// mp_dispatch_queue_process() as soon as possible. Note that wakeup_fn is
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// called under no lock, so you might have to do synchronization yourself.
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void mp_dispatch_set_wakeup_fn(struct mp_dispatch_queue *queue,
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void (*wakeup_fn)(void *wakeup_ctx),
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void *wakeup_ctx)
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{
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queue->wakeup_fn = wakeup_fn;
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queue->wakeup_ctx = wakeup_ctx;
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}
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static void mp_dispatch_append(struct mp_dispatch_queue *queue,
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struct mp_dispatch_item *item)
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{
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pthread_mutex_lock(&queue->lock);
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if (queue->tail) {
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queue->tail->next = item;
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} else {
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queue->head = item;
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}
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queue->tail = item;
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// Wake up the main thread; note that other threads might wait on this
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// condition for reasons, so broadcast the condition.
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pthread_cond_broadcast(&queue->cond);
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pthread_mutex_unlock(&queue->lock);
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if (queue->wakeup_fn)
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queue->wakeup_fn(queue->wakeup_ctx);
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}
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// Let the dispatch item process asynchronously. item->fn will be run in the
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// target thread's context, but note that mp_dispatch_enqueue() will usually
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// return long before that happens. It's up to the user to signal completion
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// of the callback. It's also up to the user to guarantee that the context
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// (fn_data) has correct lifetime, i.e. lives until the callback is run, and
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// is freed after that.
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void mp_dispatch_enqueue(struct mp_dispatch_queue *queue,
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mp_dispatch_fn fn, void *fn_data)
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{
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struct mp_dispatch_item *item = talloc_ptrtype(NULL, item);
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*item = (struct mp_dispatch_item){
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.fn = fn,
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.fn_data = fn_data,
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.asynchronous = true,
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};
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mp_dispatch_append(queue, item);
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}
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// Like mp_dispatch_enqueue(), but the queue code will call talloc_free(fn_data)
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// after the fn callback has been run. (The callback could trivially do that
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// itself, but it makes it easier to implement synchronous and asynchronous
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// requests with the same callback implementation.)
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void mp_dispatch_enqueue_autofree(struct mp_dispatch_queue *queue,
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mp_dispatch_fn fn, void *fn_data)
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{
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struct mp_dispatch_item *item = talloc_ptrtype(NULL, item);
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*item = (struct mp_dispatch_item){
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.fn = fn,
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.fn_data = talloc_steal(item, fn_data),
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.asynchronous = true,
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};
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mp_dispatch_append(queue, item);
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}
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// Run the dispatch item synchronously. item->fn will be run in the target
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// thread's context, and this function will wait until it's done.
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void mp_dispatch_run(struct mp_dispatch_queue *queue,
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mp_dispatch_fn fn, void *fn_data)
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{
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struct mp_dispatch_item item = {
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.fn = fn,
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.fn_data = fn_data,
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};
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mp_dispatch_append(queue, &item);
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pthread_mutex_lock(&queue->lock);
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while (!item.completed)
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pthread_cond_wait(&queue->cond, &queue->lock);
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pthread_mutex_unlock(&queue->lock);
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}
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// Process any outstanding dispatch items in the queue. This also handles
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// suspending or locking the target thread.
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// The timeout specifies the maximum wait time, but the actual time spent in
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// this function can be much higher if the suspending/locking functions are
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// used, or if executing the dispatch items takes time.
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// TODO: implement timeout
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void mp_dispatch_queue_process(struct mp_dispatch_queue *queue, double timeout)
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{
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pthread_mutex_lock(&queue->lock);
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queue->suspended = true;
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// Wake up thread which called mp_dispatch_suspend().
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pthread_cond_broadcast(&queue->cond);
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while (queue->head || queue->suspend_requested) {
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if (queue->head && !queue->locked) {
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struct mp_dispatch_item *item = queue->head;
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queue->head = item->next;
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if (!queue->head)
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queue->tail = NULL;
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item->next = NULL;
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// Unlock, because we want to allow other threads to queue items
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// while the dispatch item is processed.
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pthread_mutex_unlock(&queue->lock);
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item->fn(item->fn_data);
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pthread_mutex_lock(&queue->lock);
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if (item->asynchronous) {
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talloc_free(item);
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} else {
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item->completed = true;
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// Wakeup mp_dispatch_run()
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pthread_cond_broadcast(&queue->cond);
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}
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} else {
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pthread_cond_wait(&queue->cond, &queue->lock);
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}
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}
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queue->suspended = false;
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pthread_mutex_unlock(&queue->lock);
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}
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// Set the target thread into suspend mode: in this mode, the thread will enter
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// mp_dispatch_queue_process(), process any outstanding dispatch items, and
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// wait for new items when done (instead of exiting the process function).
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// Multiple threads can enter suspend mode at the same time. Suspend mode is
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// not a synchronization mechanism; it merely makes sure the target thread does
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// not leave mp_dispatch_queue_process(), even if it's done. mp_dispatch_lock()
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// can be used for exclusive access.
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void mp_dispatch_suspend(struct mp_dispatch_queue *queue)
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{
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pthread_mutex_lock(&queue->lock);
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queue->suspend_requested++;
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while (!queue->suspended)
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pthread_cond_wait(&queue->cond, &queue->lock);
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pthread_mutex_unlock(&queue->lock);
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}
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// Undo mp_dispatch_suspend().
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void mp_dispatch_resume(struct mp_dispatch_queue *queue)
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{
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pthread_mutex_lock(&queue->lock);
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assert(queue->suspend_requested > 0);
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queue->suspend_requested--;
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pthread_cond_broadcast(&queue->cond);
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pthread_mutex_unlock(&queue->lock);
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}
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// Grant exclusive access to the target thread's state. While this is active,
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// no other thread can return from mp_dispatch_lock() (i.e. it behaves like
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// a pthread mutex), and no other thread can get dispatch items completed.
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// Other threads can still queue asynchronous dispatch items without waiting,
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// and the mutex behavior applies to this function only.
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void mp_dispatch_lock(struct mp_dispatch_queue *queue)
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{
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// TODO: acquiring a lock should probably be serialized with other
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// dispatch items to guarantee minimum fairness.
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pthread_mutex_lock(&queue->lock);
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queue->suspend_requested++;
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while (1) {
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if (queue->suspended && !queue->locked) {
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queue->locked = true;
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break;
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}
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pthread_cond_wait(&queue->cond, &queue->lock);
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}
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pthread_mutex_unlock(&queue->lock);
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}
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// Undo mp_dispatch_lock().
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void mp_dispatch_unlock(struct mp_dispatch_queue *queue)
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{
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pthread_mutex_lock(&queue->lock);
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assert(queue->locked);
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assert(queue->suspend_requested > 0);
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queue->locked = false;
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queue->suspend_requested--;
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pthread_cond_broadcast(&queue->cond);
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pthread_mutex_unlock(&queue->lock);
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}
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