1SEM_TRYWAIT(3P)            POSIX Programmer's Manual           SEM_TRYWAIT(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

13       sem_trywait, sem_wait — lock a semaphore
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SYNOPSIS

16       #include <semaphore.h>
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18       int sem_trywait(sem_t *sem);
19       int sem_wait(sem_t *sem);
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DESCRIPTION

22       The sem_trywait() function shall lock the semaphore referenced  by  sem
23       only  if  the  semaphore is currently not locked; that is, if the sema‐
24       phore value is currently positive. Otherwise, it  shall  not  lock  the
25       semaphore.
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27       The  sem_wait()  function shall lock the semaphore referenced by sem by
28       performing a semaphore lock operation on that semaphore. If  the  sema‐
29       phore value is currently zero, then the calling thread shall not return
30       from the call to sem_wait() until it either locks the semaphore or  the
31       call is interrupted by a signal.
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33       Upon  successful return, the state of the semaphore shall be locked and
34       shall remain locked until  the  sem_post()  function  is  executed  and
35       returns successfully.
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37       The sem_wait() function is interruptible by the delivery of a signal.
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RETURN VALUE

40       The  sem_trywait()  and  sem_wait()  functions shall return zero if the
41       calling process successfully performed the semaphore lock operation  on
42       the  semaphore  designated  by  sem.  If the call was unsuccessful, the
43       state of the semaphore shall  be  unchanged,  and  the  function  shall
44       return a value of −1 and set errno to indicate the error.
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ERRORS

47       The sem_trywait() function shall fail if:
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49       EAGAIN The  semaphore  was  already locked, so it cannot be immediately
50              locked by the sem_trywait() operation.
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52       The sem_trywait() and sem_wait() functions may fail if:
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54       EDEADLK
55              A deadlock condition was detected.
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57       EINTR  A signal interrupted this function.
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59       EINVAL The sem argument does not refer to a valid semaphore.
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61       The following sections are informative.
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EXAMPLES

64       None.
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APPLICATION USAGE

67       Applications using these functions may be subject  to  priority  inver‐
68       sion, as discussed in the Base Definitions volume of POSIX.1‐2008, Sec‐
69       tion 3.287, Priority Inversion.
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RATIONALE

72       None.
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FUTURE DIRECTIONS

75       None.
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SEE ALSO

78       semctl(), semget(), semop(), sem_post(), sem_timedwait()
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80       The Base Definitions volume of POSIX.1‐2008,  Section  3.287,  Priority
81       Inversion, Section 4.11, Memory Synchronization, <semaphore.h>
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84       Portions  of  this text are reprinted and reproduced in electronic form
85       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
86       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
87       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
88       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
89       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  In  the
90       event of any discrepancy between this version and the original IEEE and
91       The Open Group Standard, the original IEEE and The Open Group  Standard
92       is  the  referee document. The original Standard can be obtained online
93       at http://www.unix.org/online.html .
94
95       Any typographical or formatting errors that appear  in  this  page  are
96       most likely to have been introduced during the conversion of the source
97       files to man page format. To report such errors,  see  https://www.ker‐
98       nel.org/doc/man-pages/reporting_bugs.html .
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102IEEE/The Open Group                  2013                      SEM_TRYWAIT(3P)
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