<sys/sem.h>(P) POSIX Programmer's Manual <sys/sem.h>(P)
sys/sem.h - XSI semaphore facility
The <sys/sem.h> header shall define the following constants and structures.
Semaphore operation flags:
Set up adjust on exit entry.
Command definitions for the semctl() function shall be provided as follows:
GETPID Get sempid.
GETVAL Get semval.
GETALL Get all cases of semval.
SETVAL Set semval.
SETALL Set all cases of semval.
The semid_ds structure shall contain 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_t sem_ctime Last time changed by semctl
The pid_t, time_t, key_t, and size_t types shall be defined as described in <sys/types.h>
A semaphore shall be represented by an anonymous structure containing the following mem-
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 sembuf structure shall contain 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, all of the symbols from <sys/ipc.h> shall be defined when this header is
The following sections are informative.
<sys/ipc.h> , <sys/types.h> , semctl(), semget(), semop()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 <sys/sem.h>(P)