threads: add a dispatch queue thing

Makes working with the (still) single-threaded playback thread easier.

Might be reusable for other stuff.
This commit is contained in:
wm4 2014-02-02 17:06:49 +01:00
parent dd264ebe9d
commit 20fbe2fb8c
2 changed files with 250 additions and 0 deletions

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@ -19,7 +19,9 @@
#include <unistd.h>
#include <sys/time.h>
#include <limits.h>
#include <assert.h>
#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);
}

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@ -1,6 +1,7 @@
#ifndef MP_OSDEP_THREADS_H_
#define MP_OSDEP_THREADS_H_
#include <stdbool.h>
#include <pthread.h>
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