projects / apple / xnu.git / blame
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1 | .\" $Darwin$ |
| 2 | .\" | |
| 3 | .\" Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved. | |
| 4 | .\" | |
| 5 | .\" @APPLE_LICENSE_HEADER_START@ | |
| 6 | .\" | |
| 7 | .\" The contents of this file constitute Original Code as defined in and | |
| 8 | .\" are subject to the Apple Public Source License Version 1.1 (the | |
| 9 | .\" "License"). You may not use this file except in compliance with the | |
| 10 | .\" License. Please obtain a copy of the License at | |
| 11 | .\" http://www.apple.com/publicsource and read it before using this file. | |
| 12 | .\" | |
| 13 | .\" This Original Code and all software distributed under the License are | |
| 14 | .\" distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER | |
| 15 | .\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, | |
| 16 | .\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, | |
| 17 | .\" FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the | |
| 18 | .\" License for the specific language governing rights and limitations | |
| 19 | .\" under the License. | |
| 20 | .\" | |
| 21 | .\" @APPLE_LICENSE_HEADER_END@ | |
| 22 | .\" | |
| 23 | .Dd June 8, 2000 | |
| 24 | .Dt SEM_WAIT 2 | |
| 25 | .Os Darwin | |
| 26 | .Sh NAME | |
| 27 | .Nm sem_trywait, sem_wait | |
| 28 | .Nd lock a semaphore | |
| 29 | .Sh SYNOPSIS | |
| 30 | .Fd #include <semaphore.h> | |
| 31 | .Ft int | |
| 32 | .Fn sem_trywait "sem_t *sem" | |
| 33 | .Ft int | |
| 34 | .Fn sem_wait "sem_t *sem" | |
| 35 | .Sh DESCRIPTION | |
| 36 | The semaphore referenced by | |
| 37 | .Fa sem | |
| 38 | is locked. When calling | |
| 39 | .Fn sem_wait , | |
| 40 | if the semaphore's value is zero, the calling thread will block until | |
| 41 | the lock is acquired or until the call is interrupted by a | |
| 42 | signal. Alternatively, the | |
| 43 | .Fn sem_trywait | |
| 44 | function will fail if the semaphore is already locked, rather than | |
| 45 | blocking on the semaphore. | |
| 46 | .Pp | |
| 47 | If successful (the lock was acquired), | |
| 48 | .Fn sem_wait | |
| 49 | and | |
| 50 | .Fn sem_trywait | |
| 51 | will return 0. Otherwise, -1 is returned and | |
| 52 | .Va errno | |
| 53 | is set, and the state of the semaphore is unchanged. | |
| 54 | .Sh ERRORS | |
| 55 | .Fn sem_wait | |
| 56 | and | |
| 57 | .Fn sem_trywait | |
| 58 | succeed unless: | |
| 59 | .Bl -tag -width Er | |
| 60 | .It Bq Er EAGAIN | |
| 61 | The semaphore is already locked. | |
| 62 | .It Bq Er EDEADLK | |
| 63 | A deadlock was detected. | |
| 64 | .It Bq Er EINTR | |
| 65 | The call was interrupted by a signal. | |
| 66 | .It Bq Er EINVAL | |
| 67 | .Fa sem | |
| 68 | is not a valid semaphore descriptor. | |
| 69 | .El | |
| 70 | .Sh NOTES | |
| 71 | Applications may encounter a priority inversion while using | |
| 72 | semaphores. When a thread is waiting on a semaphore which is about to | |
| 73 | be posted by a lower-priority thread and the lower-priority thread is | |
| 74 | preempted by another thread (of medium priority), a priority inversion | |
| 75 | has occured, and the higher-priority thread will be blocked for an | |
| 76 | unlimited time period. Programmers using the realtime functionality | |
| 77 | of the system should take care to avoid priority inversions. | |
| 78 | .Sh SEE ALSO | |
| 79 | .Xr sem_open 2 , | |
| 80 | .Xr sem_post 2 , | |
| 81 | .Xr semctl 2 , | |
| 82 | .Xr semget 2 , | |
| 83 | .Xr semop 2 | |
| 84 | .Sh HISTORY | |
| 85 | .Fn sem_wait | |
| 86 | and | |
| 87 | .Fn sem_trywait | |
| 88 | are specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995). |