sem(5)                                                               sem(5)

NAME
     sem - semaphore facility

SYNOPSIS
     #include <sys/sem.h>

DESCRIPTION
     The <sys/sem.h> header defines the following constants and structures.

     Semaphore operation flags:

     SEMUNDO        Set up adjust on exit entry.

     Command definitions for the function semctl():

     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 structure semidds contains the following members:

     struct ipcperm    semperm     Operation permission structure.

     unsigned short int semnsems    Number of semaphores in set.

     timet             semotime    Last semop() time.

     timet             semctime    Last time changed by semctl().

     The pidt, timet, keyt and sizet types are defined as described in
     <sys/types.h>.

     A semaphore is represented by an anonymous structure containing the
     following members:

     unsigned short int semval       Semaphore value.

     pidt              sempid       Process ID of last operation.

     unsigned short int semncnt      Number of processes waiting for semval
                                     to become greater than current value.




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sem(5)                                                               sem(5)

     unsigned short int semzcnt      Number of processes waiting for semval
                                     to become 0.

     The structure sembuf contains the following members:

     unsigned short int semnum      Semaphore number.

     short int          semop       Semaphore operation.

     short int          semflg      Operation flags.

     The following are declared as functions and may also be defined as
     macros:

     int   semctl(int semid, int semnum, int cmd, ...);
     int   semget(keyt key, int nsems, int semflg);
     int   semop(int semid, struct sembuf *sops, sizet nsops);

     In addition, all of the symbols from <sys/ipc.h> will be defined when
     this header is included.

SEE ALSO
     semctl(2), semget(2), semop(2), types(5).































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