mirror of
https://github.com/mpv-player/mpv
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22c002138d
This is almost like rendezvous(), except it allows async wakeup, and does not require global state. It will be used by a later commit. struct mp_waiter is intended to be allocated on the stack, and uses an initializer including PTHREAD_MUTEX_INITIALIZER. This is the first case in mpv that it uses PTHREAD_MUTEX_INITIALIZER for stack-allocated mutexes. It seems POSIX still does not allow this formally, but since POSIX is worth less than used toilet paper, I don't really care. Modern OSes use futexes, which means you can make _every_ memory location a lock, and this code tries to make use of it, without using OS specific code. The name of the source file is rather generic, because I intend to dump further small helpers there (or maybe move mp_rendezvous() to it).
40 lines
1.6 KiB
C
40 lines
1.6 KiB
C
#pragma once
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#include <stdint.h>
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#include <stdbool.h>
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#include <pthread.h>
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// This is basically a single-shot semaphore, intended as light-weight solution
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// for just making a thread wait for another thread.
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struct mp_waiter {
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// All fields are considered private. Use MP_WAITER_INITIALIZER to init.
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pthread_mutex_t lock;
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pthread_cond_t wakeup;
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bool done;
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uintptr_t value;
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};
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// Initialize a mp_waiter object for use with mp_waiter_*().
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#define MP_WAITER_INITIALIZER { \
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.lock = PTHREAD_MUTEX_INITIALIZER, \
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.wakeup = PTHREAD_COND_INITIALIZER, \
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}
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// Block until some other thread calls mp_waiter_wakeup(). The function returns
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// the value argument of that wakeup call. After this, the waiter object must
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// not be used anymore. Although you can reinit it with MP_WAITER_INITIALIZER
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// (then you must make sure nothing calls mp_waiter_wakeup() before this).
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uintptr_t mp_waiter_wait(struct mp_waiter *waiter);
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// Unblock the thread waiting with mp_waiter_wait(), and make it return the
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// provided value. If the other thread did not enter that call yet, it will
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// return immediately once it does (mp_waiter_wakeup() always returns
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// immediately). Calling this more than once is not allowed.
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void mp_waiter_wakeup(struct mp_waiter *waiter, uintptr_t value);
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// Query whether the waiter was woken up. If true, mp_waiter_wait() will return
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// immediately. This is useful if you want to use another way to block and
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// wakeup (in parallel to mp_waiter).
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// You still need to call mp_waiter_wait() to free resources.
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bool mp_waiter_poll(struct mp_waiter *waiter);
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