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2c731798 | 1 | '\" t |
c11b1abf | 2 | .\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> |
2c731798 | 3 | .\" |
93015253 | 4 | .\" %%%LICENSE_START(VERBATIM) |
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c13182ef | 13 | .\" |
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2c731798 | 25 | .\" |
4b8c67d9 | 26 | .TH SEM_GETVALUE 3 2017-09-15 "Linux" "Linux Programmer's Manual" |
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27 | .SH NAME |
28 | sem_getvalue \- get the value of a semaphore | |
29 | .SH SYNOPSIS | |
30 | .nf | |
31 | .B #include <semaphore.h> | |
68e4db0a | 32 | .PP |
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33 | .BI "int sem_getvalue(sem_t *" sem ", int *" sval ); |
34 | .fi | |
68e4db0a | 35 | .PP |
2c5f8c8c | 36 | Link with \fI\-pthread\fP. |
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37 | .SH DESCRIPTION |
38 | .BR sem_getvalue () | |
39 | places the current value of the semaphore pointed to | |
40 | .I sem | |
41 | into the integer pointed to by | |
42 | .IR sval . | |
847e0d88 | 43 | .PP |
c13182ef | 44 | If one or more processes or threads are blocked |
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45 | waiting to lock the semaphore with |
46 | .BR sem_wait (3), | |
4b6fa602 | 47 | POSIX.1 permits two possibilities for the value returned in |
4509e795 | 48 | .IR sval : |
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49 | either 0 is returned; |
50 | or a negative number whose absolute value is the count | |
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51 | of the number of processes and threads currently blocked in |
52 | .BR sem_wait (3). | |
d9bfdb9c | 53 | Linux adopts the former behavior. |
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54 | .SH RETURN VALUE |
55 | .BR sem_getvalue () | |
c13182ef | 56 | returns 0 on success; |
2c731798 | 57 | on error, \-1 is returned and |
c13182ef | 58 | .I errno |
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59 | is set to indicate the error. |
60 | .SH ERRORS | |
61 | .TP | |
62 | .B EINVAL | |
63 | .I sem | |
64 | is not a valid semaphore. | |
044738b4 | 65 | .SH ATTRIBUTES |
3533c7f0 PH |
66 | For an explanation of the terms used in this section, see |
67 | .BR attributes (7). | |
68 | .TS | |
69 | allbox; | |
70 | lb lb lb | |
71 | l l l. | |
72 | Interface Attribute Value | |
73 | T{ | |
044738b4 | 74 | .BR sem_getvalue () |
3533c7f0 PH |
75 | T} Thread safety MT-Safe |
76 | .TE | |
2b2581ee | 77 | .SH CONFORMING TO |
4b6fa602 | 78 | POSIX.1-2001, POSIX.1-2008. |
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79 | .SH NOTES |
80 | The value of the semaphore may already have changed by the time | |
81 | .BR sem_getvalue () | |
82 | returns. | |
47297adb | 83 | .SH SEE ALSO |
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84 | .BR sem_post (3), |
85 | .BR sem_wait (3), | |
86 | .BR sem_overview (7) |