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d1babeb32d
Replace atomic_increment and atomic_increment_val with atomic_fetch_add_relaxed. One case in sem_post.c uses release semantics (see comment above it). The others are simple counters and do not protect any shared data from concurrent accesses. Passes regress on AArch64. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
117 lines
4.0 KiB
Plaintext
117 lines
4.0 KiB
Plaintext
@node Inter-Process Communication, Job Control, Processes, Top
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@c %MENU% All about inter-process communication
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@chapter Inter-Process Communication
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@cindex ipc
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This chapter describes the @glibcadj{} inter-process communication primitives.
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@menu
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* Semaphores:: Support for creating and managing semaphores
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@end menu
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@node Semaphores
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@section Semaphores
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@Theglibc{} implements the semaphore APIs as defined in POSIX and
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System V. Semaphores can be used by multiple processes to coordinate shared
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resources. The following is a complete list of the semaphore functions provided
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by @theglibc{}.
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@c Need descriptions for all of these functions.
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@subsection System V Semaphores
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@deftypefun int semctl (int @var{semid}, int @var{semnum}, int @var{cmd});
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@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{/linux}}}
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@c syscall(ipc) ok
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@c
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@c AC-unsafe because we need to translate the new kernel
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@c semid_ds buf into the userspace layout. Cancellation
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@c at that point results in an inconsistent userspace
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@c semid_ds.
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@end deftypefun
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@deftypefun int semget (key_t @var{key}, int @var{nsems}, int @var{semflg});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c syscall(ipc) ok
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@end deftypefun
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@deftypefun int semop (int @var{semid}, struct sembuf *@var{sops}, size_t @var{nsops});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c syscall(ipc) ok
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@end deftypefun
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@deftypefun int semtimedop (int @var{semid}, struct sembuf *@var{sops}, size_t @var{nsops}, const struct timespec *@var{timeout});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c syscall(ipc) ok
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@end deftypefun
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@subsection POSIX Semaphores
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@deftypefun int sem_init (sem_t *@var{sem}, int @var{pshared}, unsigned int @var{value});
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@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}}
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@c Does not atomically update sem_t therefore AC-unsafe
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@c because it can leave sem_t partially initialized.
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@end deftypefun
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@deftypefun int sem_destroy (sem_t *@var{sem});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c Function does nothing and is therefore always safe.
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@end deftypefun
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@deftypefun sem_t *sem_open (const char *@var{name}, int @var{oflag}, ...);
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@safety{@prelim{}@mtsafe{}@asunsafe{@asuinit{}}@acunsafe{@acuinit{}}}
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@c pthread_once asuinit
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@c
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@c We are AC-Unsafe becuase we use pthread_once to initialize
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@c a global variable that holds the location of the mounted
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@c shmfs on Linux.
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@end deftypefun
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@deftypefun int sem_close (sem_t *@var{sem});
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@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{}}}
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@c lll_lock asulock aculock
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@c twalk mtsrace{:root}
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@c
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@c We are AS-unsafe because we take a non-recursive lock.
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@c We are AC-unsafe because several internal data structures
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@c are not updated atomically.
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@end deftypefun
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@deftypefun int sem_unlink (const char *@var{name});
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@safety{@prelim{}@mtsafe{}@asunsafe{@asuinit{}}@acunsafe{@acucorrupt{}}}
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@c pthread_once asuinit acucorrupt aculock
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@c mempcpy acucorrupt
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@end deftypefun
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@deftypefun int sem_wait (sem_t *@var{sem});
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@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}}
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@c atomic_fetch_add_relaxed (nwaiters) acucorrupt
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@c
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@c Given the use atomic operations this function seems
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@c to be AS-safe. It is AC-unsafe because there is still
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@c a window between atomic_fetch_add_relaxed and the pthread_push
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@c of the handler that undoes that operation. A cancellation
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@c at that point would fail to remove the process from the
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@c waiters count.
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@end deftypefun
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@deftypefun int sem_timedwait (sem_t *@var{sem}, const struct timespec *@var{abstime});
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@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}}
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@c Same safety issues as sem_wait.
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@end deftypefun
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@deftypefun int sem_trywait (sem_t *@var{sem});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c All atomic operations are safe in all contexts.
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@end deftypefun
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@deftypefun int sem_post (sem_t *@var{sem});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c Same safety as sem_trywait.
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@end deftypefun
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@deftypefun int sem_getvalue (sem_t *@var{sem}, int *@var{sval});
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@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
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@c Atomic write of a value is safe in all contexts.
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@end deftypefun
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