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


NAME
       semaphore.h — semaphores


SYNOPSIS
       #include <semaphore.h>


DESCRIPTION
       The  <semaphore.h>  header  shall  define  the  sem_t  type,  used in performing semaphore
       operations. The semaphore may be implemented  using  a  file  descriptor,  in  which  case
       applications are able to open up at least a total of {OPEN_MAX} files and semaphores.

       The  <semaphore.h>  header  shall define the symbolic constant SEM_FAILED which shall have
       type sem_t *.

       The following shall be declared as functions and may also be defined as  macros.  Function
       prototypes shall be provided.

           int    sem_close(sem_t *);
           int    sem_destroy(sem_t *);
           int    sem_getvalue(sem_t *restrict, int *restrict);
           int    sem_init(sem_t *, int, unsigned);
           sem_t *sem_open(const char *, int, ...);
           int    sem_post(sem_t *);
           int    sem_timedwait(sem_t *restrict, const struct timespec *restrict);
           int    sem_trywait(sem_t *);
           int    sem_unlink(const char *);
           int    sem_wait(sem_t *);

       Inclusion  of  the  <semaphore.h> header may make visible symbols defined in the <fcntl.h>
       and <time.h> headers.

       The following sections are informative.


APPLICATION USAGE
       None.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       <fcntl.h>, <sys_types.h>, <time.h>

       The System Interfaces volume of POSIX.1‐2017, sem_close(), sem_destroy(),  sem_getvalue(),
       sem_init(), sem_open(), sem_post(), sem_timedwait(), sem_trywait(), sem_unlink()


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 .