projects / thirdparty / man-pages.git / blame
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1 | '\" t |
| 2 | .\" Hey Emacs! This file is -*- nroff -*- source. | |
| 3 | .\" | |
| 4 | .\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net> | |
| 5 | .\" | |
| 6 | .\" Permission is granted to make and distribute verbatim copies of this | |
| 7 | .\" manual provided the copyright notice and this permission notice are | |
| 8 | .\" preserved on all copies. | |
| 9 | .\" | |
| 10 | .\" Permission is granted to copy and distribute modified versions of this | |
| 11 | .\" manual under the conditions for verbatim copying, provided that the | |
| 12 | .\" entire resulting derived work is distributed under the terms of a | |
| 13 | .\" permission notice identical to this one. | |
| c13182ef | 14 | .\" |
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15 | .\" Since the Linux kernel and libraries are constantly changing, this |
| 16 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
| 17 | .\" responsibility for errors or omissions, or for damages resulting from | |
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18 | .\" the use of the information contained herein. |
| 19 | .\" | |
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20 | .\" Formatted or processed versions of this manual, if unaccompanied by |
| 21 | .\" the source, must acknowledge the copyright and authors of this work. | |
| 22 | .\" | |
| 23 | .TH SEM_GETVALUE 3 2006-03-25 "Linux 2.6.16" "Linux Programmer's Manual" | |
| 24 | .SH NAME | |
| 25 | sem_getvalue \- get the value of a semaphore | |
| 26 | .SH SYNOPSIS | |
| 27 | .nf | |
| 28 | .B #include <semaphore.h> | |
| 29 | .sp | |
| 30 | .BI "int sem_getvalue(sem_t *" sem ", int *" sval ); | |
| 31 | .fi | |
| 32 | .SH DESCRIPTION | |
| 33 | .BR sem_getvalue () | |
| 34 | places the current value of the semaphore pointed to | |
| 35 | .I sem | |
| 36 | into the integer pointed to by | |
| 37 | .IR sval . | |
| 38 | ||
| c13182ef | 39 | If one or more processes or threads are blocked |
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40 | waiting to lock the semaphore with |
| 41 | .BR sem_wait (3), | |
| c13182ef | 42 | POSIX.1-2001 permits two possibilities for the value returned in |
| 4509e795 | 43 | .IR sval : |
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44 | either 0 is returned; |
| 45 | or a negative number whose absolute value is the count | |
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46 | of the number of processes and threads currently blocked in |
| 47 | .BR sem_wait (3). | |
| 48 | Linux adopts the former behaviour. | |
| 49 | .SH RETURN VALUE | |
| 50 | .BR sem_getvalue () | |
| c13182ef | 51 | returns 0 on success; |
| 2c731798 | 52 | on error, \-1 is returned and |
| c13182ef | 53 | .I errno |
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54 | is set to indicate the error. |
| 55 | .SH ERRORS | |
| 56 | .TP | |
| 57 | .B EINVAL | |
| 58 | .I sem | |
| 59 | is not a valid semaphore. | |
| 60 | .SH NOTES | |
| 61 | The value of the semaphore may already have changed by the time | |
| 62 | .BR sem_getvalue () | |
| 63 | returns. | |
| 64 | .SH CONFORMING TO | |
| 65 | POSIX.1-2001. | |
| 66 | .SH "SEE ALSO" | |
| 67 | .BR sem_post (3), | |
| 68 | .BR sem_wait (3), | |
| 69 | .BR sem_overview (7) |