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

       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 .