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Diffstat (limited to 'zix')
| -rw-r--r-- | zix/sem.h | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/zix/sem.h b/zix/sem.h new file mode 100644 index 0000000..6b66a51 --- /dev/null +++ b/zix/sem.h @@ -0,0 +1,183 @@ +/* + Copyright 2012 David Robillard <http://drobilla.net> + + 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. + + THIS 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. +*/ + +#ifndef ZIX_SEM_H +#define ZIX_SEM_H + +#include <stdbool.h> + +#ifdef __APPLE__ +# include <limits.h> +# include <CoreServices/CoreServices.h> +#else +# include <semaphore.h> +#endif + +#include "zix/common.h" + +#ifdef __cplusplus +extern "C" { +#endif + +/** + @addtogroup zix + @{ + @name Semaphore + @{ +*/ + +/** + A counting semaphore. + + This is an integer that is always positive, and has two main operations: + increment (post) and decrement (wait). If a decrement can not be performed + (i.e. the value is 0) the caller will be blocked until another thread posts + and the operation can succeed. + + Semaphores can be created with any starting value, but typically this will + be 0 so the semaphore can be used as a simple signal where each post + corresponds to one wait. + + Semaphores are very efficient (much moreso than a mutex/cond pair). In + particular, at least on Linux, post is async-signal-safe, which means it + does not block and will not be interrupted. If you need to signal from + a realtime thread, this is the most appropriate primitive to use. +*/ +typedef struct ZixSemImpl ZixSem; + +/** + Create and initialize @c sem to @c initial. +*/ +static inline ZixStatus +zix_sem_init(ZixSem* sem, unsigned initial); + +/** + Destroy @c sem. +*/ +static inline void +zix_sem_destroy(ZixSem* sem); + +/** + Increment (and signal any waiters). + Realtime safe. +*/ +static inline void +zix_sem_post(ZixSem* sem); + +/** + Wait until count is > 0, then decrement. + Obviously not realtime safe. +*/ +static inline void +zix_sem_wait(ZixSem* sem); + +/** + Non-blocking version of wait(). + + @return true if decrement was successful (lock was acquired). +*/ +static inline bool +zix_sem_try_wait(ZixSem* sem); + +#ifdef __APPLE__ + +struct ZixSemImpl { + MPSemaphoreID sem; +}; + +static inline ZixStatus +zix_sem_init(ZixSem* sem, unsigned initial) +{ + MPCreateSemaphore(UINT_MAX, initial, &_sem); +} + +static inline void +zix_sem_destroy(ZixSem* sem) +{ + MPDeleteSemaphore(_sem); +} + +static inline void +zix_sem_post(ZixSem* sem) +{ + MPSignalSemaphore(_sem); +} + +static inline void +zix_sem_wait(ZixSem* sem) +{ + MPWaitOnSemaphore(sem->sem, kDurationForever); +} + +static inline bool +zix_sem_try_wait(ZixSem* sem) +{ + return MPWaitOnSemaphore(sem->sem, kDurationImmediate) == noErr; +} + +#else /* !defined(__APPLE__) */ + +struct ZixSemImpl { + sem_t sem; +}; + +static inline ZixStatus +zix_sem_init(ZixSem* sem, unsigned initial) +{ + return sem_init(&sem->sem, 0, initial) + ? ZIX_STATUS_SUCCESS : ZIX_STATUS_ERROR; +} + +static inline void +zix_sem_destroy(ZixSem* sem) +{ + sem_destroy(&sem->sem); +} + +static inline void +zix_sem_post(ZixSem* sem) +{ + sem_post(&sem->sem); +} + +static inline void +zix_sem_wait(ZixSem* sem) +{ + /* Note that sem_wait always returns 0 in practice, except in + gdb (at least), where it returns nonzero, so the while is + necessary (and is the correct/safe solution in any case). + */ + while (sem_wait(&sem->sem) != 0) {} +} + +static inline bool +zix_sem_try_wait(ZixSem* sem) +{ + return (sem_trywait(&sem->sem) == 0); +} + +#endif + +/** + @} + @} +*/ + +#ifdef __cplusplus +} /* extern "C" */ +#endif + +#endif /* ZIX_SEM_H */ |