mpv/misc/thread_tools.c

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/* Copyright (C) 2018 the mpv developers
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <assert.h>
#include <errno.h>
#include <stdatomic.h>
#include <string.h>
#include <sys/types.h>
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#ifdef _WIN32
#include <windows.h>
#else
#include <poll.h>
#endif
#include "common/common.h"
#include "misc/linked_list.h"
#include "osdep/io.h"
#include "osdep/timer.h"
#include "thread_tools.h"
uintptr_t mp_waiter_wait(struct mp_waiter *waiter)
{
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mp_mutex_lock(&waiter->lock);
while (!waiter->done)
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mp_cond_wait(&waiter->wakeup, &waiter->lock);
mp_mutex_unlock(&waiter->lock);
uintptr_t ret = waiter->value;
// We document that after mp_waiter_wait() the waiter object becomes
// invalid. (It strictly returns only after mp_waiter_wakeup() has returned,
// and the object is "single-shot".) So destroy it here.
// Normally, we expect that the system uses futexes, in which case the
// following functions will do nearly nothing. This is true for Windows
// and Linux. But some lesser OSes still might allocate kernel objects
// when initializing mutexes, so destroy them here.
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mp_mutex_destroy(&waiter->lock);
mp_cond_destroy(&waiter->wakeup);
memset(waiter, 0xCA, sizeof(*waiter)); // for debugging
return ret;
}
void mp_waiter_wakeup(struct mp_waiter *waiter, uintptr_t value)
{
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mp_mutex_lock(&waiter->lock);
assert(!waiter->done);
waiter->done = true;
waiter->value = value;
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mp_cond_signal(&waiter->wakeup);
mp_mutex_unlock(&waiter->lock);
}
bool mp_waiter_poll(struct mp_waiter *waiter)
{
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mp_mutex_lock(&waiter->lock);
bool r = waiter->done;
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mp_mutex_unlock(&waiter->lock);
return r;
}
struct mp_cancel {
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mp_mutex lock;
mp_cond wakeup;
// Semaphore state and "mirrors".
atomic_bool triggered;
void (*cb)(void *ctx);
void *cb_ctx;
int wakeup_pipe[2];
void *win32_event; // actually HANDLE
// Slave list. These are automatically notified as well.
struct {
struct mp_cancel *head, *tail;
} slaves;
// For slaves. Synchronization is managed by parent.lock!
struct mp_cancel *parent;
struct {
struct mp_cancel *next, *prev;
} siblings;
};
static void cancel_destroy(void *p)
{
struct mp_cancel *c = p;
assert(!c->slaves.head); // API user error
mp_cancel_set_parent(c, NULL);
if (c->wakeup_pipe[0] >= 0) {
close(c->wakeup_pipe[0]);
close(c->wakeup_pipe[1]);
}
#ifdef __MINGW32__
if (c->win32_event)
CloseHandle(c->win32_event);
#endif
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mp_mutex_destroy(&c->lock);
mp_cond_destroy(&c->wakeup);
}
struct mp_cancel *mp_cancel_new(void *talloc_ctx)
{
struct mp_cancel *c = talloc_ptrtype(talloc_ctx, c);
talloc_set_destructor(c, cancel_destroy);
*c = (struct mp_cancel){
.triggered = false,
.wakeup_pipe = {-1, -1},
};
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mp_mutex_init(&c->lock);
mp_cond_init(&c->wakeup);
return c;
}
static void trigger_locked(struct mp_cancel *c)
{
atomic_store(&c->triggered, true);
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mp_cond_broadcast(&c->wakeup); // condition bound to c->triggered
if (c->cb)
c->cb(c->cb_ctx);
for (struct mp_cancel *sub = c->slaves.head; sub; sub = sub->siblings.next)
mp_cancel_trigger(sub);
if (c->wakeup_pipe[1] >= 0)
(void)write(c->wakeup_pipe[1], &(char){0}, 1);
#ifdef __MINGW32__
if (c->win32_event)
SetEvent(c->win32_event);
#endif
}
void mp_cancel_trigger(struct mp_cancel *c)
{
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mp_mutex_lock(&c->lock);
trigger_locked(c);
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mp_mutex_unlock(&c->lock);
}
void mp_cancel_reset(struct mp_cancel *c)
{
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mp_mutex_lock(&c->lock);
atomic_store(&c->triggered, false);
if (c->wakeup_pipe[0] >= 0) {
// Flush it fully.
while (1) {
int r = read(c->wakeup_pipe[0], &(char[256]){0}, 256);
if (r <= 0 && !(r < 0 && errno == EINTR))
break;
}
}
#ifdef __MINGW32__
if (c->win32_event)
ResetEvent(c->win32_event);
#endif
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mp_mutex_unlock(&c->lock);
}
bool mp_cancel_test(struct mp_cancel *c)
{
return c ? atomic_load_explicit(&c->triggered, memory_order_relaxed) : false;
}
bool mp_cancel_wait(struct mp_cancel *c, double timeout)
{
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int64_t wait_until = mp_time_ns_add(mp_time_ns(), timeout);
mp_mutex_lock(&c->lock);
while (!mp_cancel_test(c)) {
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if (mp_cond_timedwait_until(&c->wakeup, &c->lock, wait_until))
break;
}
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mp_mutex_unlock(&c->lock);
return mp_cancel_test(c);
}
// If a new notification mechanism was added, and the mp_cancel state was
// already triggered, make sure the newly added mechanism is also triggered.
static void retrigger_locked(struct mp_cancel *c)
{
if (mp_cancel_test(c))
trigger_locked(c);
}
void mp_cancel_set_cb(struct mp_cancel *c, void (*cb)(void *ctx), void *ctx)
{
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mp_mutex_lock(&c->lock);
c->cb = cb;
c->cb_ctx = ctx;
retrigger_locked(c);
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mp_mutex_unlock(&c->lock);
}
void mp_cancel_set_parent(struct mp_cancel *slave, struct mp_cancel *parent)
{
// We can access c->parent without synchronization, because:
// - concurrent mp_cancel_set_parent() calls to slave are not allowed
// - slave->parent needs to stay valid as long as the slave exists
if (slave->parent == parent)
return;
if (slave->parent) {
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mp_mutex_lock(&slave->parent->lock);
LL_REMOVE(siblings, &slave->parent->slaves, slave);
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mp_mutex_unlock(&slave->parent->lock);
}
slave->parent = parent;
if (slave->parent) {
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mp_mutex_lock(&slave->parent->lock);
LL_APPEND(siblings, &slave->parent->slaves, slave);
retrigger_locked(slave->parent);
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mp_mutex_unlock(&slave->parent->lock);
}
}
int mp_cancel_get_fd(struct mp_cancel *c)
{
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mp_mutex_lock(&c->lock);
if (c->wakeup_pipe[0] < 0) {
#if defined(__GNUC__) && !defined(__clang__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wstringop-overflow="
#endif
mp_make_wakeup_pipe(c->wakeup_pipe);
#if defined(__GNUC__) && !defined(__clang__)
# pragma GCC diagnostic pop
#endif
retrigger_locked(c);
}
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mp_mutex_unlock(&c->lock);
return c->wakeup_pipe[0];
}
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#ifdef _WIN32
void *mp_cancel_get_event(struct mp_cancel *c)
{
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mp_mutex_lock(&c->lock);
if (!c->win32_event) {
c->win32_event = CreateEventW(NULL, TRUE, FALSE, NULL);
retrigger_locked(c);
}
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mp_mutex_unlock(&c->lock);
return c->win32_event;
}
#endif