sem_init(3p)

1SEM_INIT(3P)               POSIX Programmer's Manual              SEM_INIT(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

12       sem_init - initialize an unnamed semaphore (REALTIME)
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SYNOPSIS

15       #include <semaphore.h>
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17       int sem_init(sem_t *sem, int pshared, unsigned value);
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DESCRIPTION

21       The sem_init() function shall initialize the unnamed semaphore referred
22       to  by sem. The value of the initialized semaphore shall be value. Fol‐
23       lowing a successful call to sem_init(), the semaphore may  be  used  in
24       subsequent   calls   to   sem_wait(),  sem_trywait(),  sem_post(),  and
25       sem_destroy().  This semaphore shall remain usable until the  semaphore
26       is destroyed.
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28       If  the  pshared  argument  has a non-zero value, then the semaphore is
29       shared between processes; in this case, any process that can access the
30       semaphore  sem  can  use  sem for performing sem_wait(), sem_trywait(),
31       sem_post(), and sem_destroy() operations.
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33       Only sem itself may be used for performing synchronization.  The result
34       of  referring  to  copies of sem in calls to sem_wait(), sem_trywait(),
35       sem_post(), and sem_destroy() is undefined.
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37       If the pshared argument is zero, then the semaphore is  shared  between
38       threads of the process; any thread in this process can use sem for per‐
39       forming sem_wait(), sem_trywait(), sem_post(), and sem_destroy() opera‐
40       tions.  The use of the semaphore by threads other than those created in
41       the same process is undefined.
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43       Attempting to initialize an already initialized  semaphore  results  in
44       undefined behavior.
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RETURN VALUE

47       Upon  successful  completion,  the sem_init() function shall initialize
48       the semaphore in sem. Otherwise, it shall return -1 and  set  errno  to
49       indicate the error.
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ERRORS

52       The sem_init() function shall fail if:
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54       EINVAL The value argument exceeds {SEM_VALUE_MAX}.
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56       ENOSPC A  resource  required  to  initialize  the  semaphore  has  been
57              exhausted, or the limit on  semaphores  (  {SEM_NSEMS_MAX})  has
58              been reached.
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60       EPERM  The  process  lacks the appropriate privileges to initialize the
61              semaphore.
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64       The following sections are informative.
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EXAMPLES

67       None.
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APPLICATION USAGE

70       The sem_init() function is part of the Semaphores option and  need  not
71       be available on all implementations.
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RATIONALE

74       Although  this  volume  of IEEE Std 1003.1-2001 fails to specify a suc‐
75       cessful return value, it is likely that a later version may require the
76       implementation  to  return a value of zero if the call to sem_init() is
77       successful.
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FUTURE DIRECTIONS

80       None.
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COPYRIGHT

87       Portions  of  this text are reprinted and reproduced in electronic form
88       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
89       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
90       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
91       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
92       event of any discrepancy between this version and the original IEEE and
93       The  Open Group Standard, the original IEEE and The Open Group Standard
94       is the referee document. The original Standard can be  obtained  online
95       at http://www.opengroup.org/unix/online.html .
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99IEEE/The Open Group                  2003                         SEM_INIT(3P)