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

       sys/sem.h — XSI semaphore facility

SYNOPSIS

       #include <sys/sem.h>

DESCRIPTION

       The <sys/sem.h> header shall define the following symbolic constant for use as a semaphore
       operation flag:

       SEM_UNDO    Set up adjust on exit entry.

       The <sys/sem.h> header shall define the following symbolic constants for use  as  commands
       for the semctl() function:

       GETNCNT     Get semncnt.

       GETPID      Get sempid.

       GETVAL      Get semval.

       GETALL      Get all cases of semval.

       GETZCNT     Get semzcnt.

       SETVAL      Set semval.

       SETALL      Set all cases of semval.

       The  <sys/sem.h>  header  shall  define  the  semid_ds  structure, which shall include the
       following members:

           struct ipc_perm  sem_perm  Operation permission structure.
           unsigned short   sem_nsems Number of semaphores in set.
           time_t           sem_otime Last semop() time.
           time_t           sem_ctime Last time changed by semctl().

       The <sys/sem.h> header shall define the pid_t, size_t, and time_t types  as  described  in
       <sys/types.h>.

       A  semaphore  shall  be  represented  by  an  anonymous structure, which shall include the
       following members:

           unsigned short  semval   Semaphore value.
           pid_t           sempid   Process ID of last operation.
           unsigned short  semncnt  Number of processes waiting for semval
                                    to become greater than current value.
           unsigned short  semzcnt  Number of processes waiting for semval
                                    to become 0.

       The <sys/sem.h> header  shall  define  the  sembuf  structure,  which  shall  include  the
       following members:

           unsigned short  sem_num   Semaphore number.
           short           sem_op    Semaphore operation.
           short           sem_flg   Operation flags.

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

           int   semctl(int, int, int, ...);
           int   semget(key_t, int, int);
           int   semop(int, struct sembuf *, size_t);

       In addition, the <sys/sem.h> header shall include the <sys/ipc.h> header.

       The following sections are informative.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <sys_ipc.h>, <sys_types.h>

       The System Interfaces volume of POSIX.1‐2017, semctl(), semget(), semop()

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 .