From 20fbe2fb8c1b3b4f5b08dd529ac1897f24c88a95 Mon Sep 17 00:00:00 2001 From: wm4 Date: Sun, 2 Feb 2014 17:06:49 +0100 Subject: [PATCH] threads: add a dispatch queue thing Makes working with the (still) single-threaded playback thread easier. Might be reusable for other stuff. --- osdep/threads.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++++ osdep/threads.h | 21 +++++ 2 files changed, 250 insertions(+) diff --git a/osdep/threads.c b/osdep/threads.c index dcc3965b1d..0f72599641 100644 --- a/osdep/threads.c +++ b/osdep/threads.c @@ -19,7 +19,9 @@ #include #include #include +#include +#include "common/common.h" #include "threads.h" static void get_pthread_time(struct timespec *out_ts) @@ -78,3 +80,230 @@ int mpthread_mutex_init_recursive(pthread_mutex_t *mutex) pthread_mutexattr_destroy(&attr); return r; } + +struct mp_dispatch_queue { + struct mp_dispatch_item *head, *tail; + pthread_mutex_t lock; + pthread_cond_t cond; + int suspend_requested; + bool suspended; + bool locked; + void (*wakeup_fn)(void *wakeup_ctx); + void *wakeup_ctx; +}; + +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->suspend_requested); + assert(!queue->suspended); + assert(!queue->locked); + pthread_cond_destroy(&queue->cond); + pthread_mutex_destroy(&queue->lock); +} + +// A dispatch queue lets other threads runs callbacks in s target thread. +// The target thread is the thread which created the queue and which calls +// mp_dispatch_queue_process(). +// Free the dispatch queue with talloc_free(). (It must be empty.) +struct mp_dispatch_queue *mp_dispatch_create(void *talloc_parent) +{ + struct mp_dispatch_queue *queue = talloc_ptrtype(talloc_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); + pthread_mutex_unlock(&queue->lock); + if (queue->wakeup_fn) + queue->wakeup_fn(queue->wakeup_ctx); +} + +// Let the dispatch item process asynchronously. item->fn will be run in the +// target thread's context, but 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 the dispatch item synchronously. item->fn will be run in the target +// thread's context, and this function will wait until it's done. +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 target thread. +// The timeout specifies the maximum wait time, but 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. +// TODO: implement timeout +void mp_dispatch_queue_process(struct mp_dispatch_queue *queue, double timeout) +{ + pthread_mutex_lock(&queue->lock); + queue->suspended = true; + // Wake up thread which called mp_dispatch_suspend(). + pthread_cond_broadcast(&queue->cond); + while (queue->head || queue->suspend_requested) { + if (queue->head && !queue->locked) { + 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. + pthread_mutex_unlock(&queue->lock); + item->fn(item->fn_data); + pthread_mutex_lock(&queue->lock); + if (item->asynchronous) { + talloc_free(item); + } else { + item->completed = true; + // Wakeup mp_dispatch_run() + pthread_cond_broadcast(&queue->cond); + } + } else { + pthread_cond_wait(&queue->cond, &queue->lock); + } + } + queue->suspended = false; + pthread_mutex_unlock(&queue->lock); +} + +// Set the target thread into suspend mode: in this mode, the thread will enter +// mp_dispatch_queue_process(), process any outstanding dispatch items, and +// wait for new items when done (instead of exiting the process function). +// Multiple threads can enter suspend mode at the same time. Suspend mode is +// not a synchronization mechanism; it merely makes sure the target thread does +// not leave mp_dispatch_queue_process(), even if it's done. mp_dispatch_lock() +// can be used for exclusive access. +void mp_dispatch_suspend(struct mp_dispatch_queue *queue) +{ + pthread_mutex_lock(&queue->lock); + queue->suspend_requested++; + while (!queue->suspended) + pthread_cond_wait(&queue->cond, &queue->lock); + pthread_mutex_unlock(&queue->lock); +} + +// Undo mp_dispatch_suspend(). +void mp_dispatch_resume(struct mp_dispatch_queue *queue) +{ + pthread_mutex_lock(&queue->lock); + assert(queue->suspend_requested > 0); + queue->suspend_requested--; + 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) +{ + // TODO: acquiring a lock should probably be serialized with other + // dispatch items to guarantee minimum fairness. + pthread_mutex_lock(&queue->lock); + queue->suspend_requested++; + while (1) { + if (queue->suspended && !queue->locked) { + queue->locked = true; + break; + } + pthread_cond_wait(&queue->cond, &queue->lock); + } + pthread_mutex_unlock(&queue->lock); +} + +// Undo mp_dispatch_lock(). +void mp_dispatch_unlock(struct mp_dispatch_queue *queue) +{ + pthread_mutex_lock(&queue->lock); + assert(queue->locked); + assert(queue->suspend_requested > 0); + queue->locked = false; + queue->suspend_requested--; + pthread_cond_broadcast(&queue->cond); + pthread_mutex_unlock(&queue->lock); +} diff --git a/osdep/threads.h b/osdep/threads.h index 3d060009cb..3eb4ce2ffc 100644 --- a/osdep/threads.h +++ b/osdep/threads.h @@ -1,6 +1,7 @@ #ifndef MP_OSDEP_THREADS_H_ #define MP_OSDEP_THREADS_H_ +#include #include struct timespec mpthread_get_deadline(double timeout); @@ -10,4 +11,24 @@ int mpthread_cond_timed_wait(pthread_cond_t *cond, pthread_mutex_t *mutex, int mpthread_mutex_init_recursive(pthread_mutex_t *mutex); + +typedef void (*mp_dispatch_fn)(void *data); +struct mp_dispatch_queue; + +struct mp_dispatch_queue *mp_dispatch_create(void *talloc_parent); +void mp_dispatch_set_wakeup_fn(struct mp_dispatch_queue *queue, + void (*wakeup_fn)(void *wakeup_ctx), + void *wakeup_ctx); +void mp_dispatch_enqueue(struct mp_dispatch_queue *queue, + mp_dispatch_fn fn, void *fn_data); +void mp_dispatch_enqueue_autofree(struct mp_dispatch_queue *queue, + mp_dispatch_fn fn, void *fn_data); +void mp_dispatch_run(struct mp_dispatch_queue *queue, + mp_dispatch_fn fn, void *fn_data); +void mp_dispatch_queue_process(struct mp_dispatch_queue *queue, double timeout); +void mp_dispatch_suspend(struct mp_dispatch_queue *queue); +void mp_dispatch_resume(struct mp_dispatch_queue *queue); +void mp_dispatch_lock(struct mp_dispatch_queue *queue); +void mp_dispatch_unlock(struct mp_dispatch_queue *queue); + #endif