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



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

NAME
       sem_init -- initialize an unnamed semaphore

SYNOPSIS
       #include <semaphore.h>

       int sem_init(sem_t *sem, int pshared, unsigned value);

DESCRIPTION
       The sem__init() function shall initialize the unnamed semaphore referred
       to by sem.  The value of the initialized semaphore shall be value.
       Following a successful call to sem__init(), the semaphore may be used in
       subsequent calls to sem__wait(), sem__timedwait(), sem__trywait(),
       sem__post(), and sem__destroy().  This semaphore shall remain usable
       until the semaphore is destroyed.

       If the pshared argument has a non-zero value, then the semaphore is
       shared between processes; in this case, any process that can access the
       semaphore sem can use sem for performing sem__wait(), sem__timedwait(),
       sem__trywait(), sem__post(), and sem__destroy() operations.

       If the pshared argument is zero, then the semaphore is shared between
       threads of the process; any thread in this process can use sem for
       performing sem__wait(), sem__timedwait(), sem__trywait(), sem__post(), and
       sem__destroy() operations.

       See Section 2.9.9, Synchronization Object Copies and Alternative
       Mappings for further requirements.

       Attempting to initialize an already initialized semaphore results in
       undefined behavior.

RETURN VALUE
       Upon successful completion, the sem__init() function shall initialize
       the semaphore in sem and return 0. Otherwise, it shall return -1 and
       set errno to indicate the error.

ERRORS
       The sem__init() function shall fail if:

       EINVAL The value argument exceeds {SEM_VALUE_MAX}.

       ENOSPC A resource required to initialize the semaphore has been
              exhausted, or the limit on semaphores ({SEM_NSEMS_MAX}) has been
              reached.

       EPERM  The process lacks appropriate privileges to initialize the
              semaphore.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sem__destroy(), sem__post(), sem__timedwait(), sem__trywait()

       The Base Definitions volume of POSIX.1-2017, <semaphore.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          SEM_INIT(3)
