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| .TH SEM_GETVALUE 3 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| sem_getvalue \- get the value of a semaphore |
| .SH SYNOPSIS |
| .nf |
| .B #include <semaphore.h> |
| .PP |
| .BI "int sem_getvalue(sem_t *restrict " sem ", int *restrict " sval ); |
| .fi |
| .PP |
| Link with \fI\-pthread\fP. |
| .SH DESCRIPTION |
| .BR sem_getvalue () |
| places the current value of the semaphore pointed to |
| .I sem |
| into the integer pointed to by |
| .IR sval . |
| .PP |
| If one or more processes or threads are blocked |
| waiting to lock the semaphore with |
| .BR sem_wait (3), |
| POSIX.1 permits two possibilities for the value returned in |
| .IR sval : |
| either 0 is returned; |
| or a negative number whose absolute value is the count |
| of the number of processes and threads currently blocked in |
| .BR sem_wait (3). |
| Linux adopts the former behavior. |
| .SH RETURN VALUE |
| .BR sem_getvalue () |
| returns 0 on success; |
| on error, \-1 is returned and |
| .I errno |
| is set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EINVAL |
| .I sem |
| is not a valid semaphore. |
| (The glibc implementation currently does not check whether |
| .I sem |
| is valid.) |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR sem_getvalue () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008. |
| .SH NOTES |
| The value of the semaphore may already have changed by the time |
| .BR sem_getvalue () |
| returns. |
| .SH SEE ALSO |
| .BR sem_post (3), |
| .BR sem_wait (3), |
| .BR sem_overview (7) |