semget(2) [opendarwin man page]

SEMGET(2)						      BSD System Calls Manual							 SEMGET(2)

NAME

     semget -- obtain a semaphore id

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/sem.h>

     int
     semget(key_t key, int nsems, int flag);

DESCRIPTION

     Based on the values of key and flag, semget() returns the identifier of a newly created or previously existing set of semaphores.	The key is
     analogous to a filename: it provides a handle that names an IPC object.  There are three ways to specify a key:

     o	 IPC_PRIVATE may be specified, in which case a new IPC object will be created.

     o	 An integer constant may be specified.	If no IPC object corresponding to key is specified and the IPC_CREAT bit is set in flag, a new one
	 will be created.

     o	 The ftok(3) function may be used to generate a key from a pathname.

     The mode of a newly created IPC object is determined by OR'ing the following constants into the flag argument:

     SEM_R	   Read access for user.

     SEM_A	   Alter access for user.

     (SEM_R>>3)    Read access for group.

     (SEM_A>>3)    Alter access for group.

     (SEM_R>>6)    Read access for other.

     (SEM_A>>6)    Alter access for other.

     If a new set of semaphores is being created, nsems is used to indicate the number of semaphores the set should contain.  Otherwise, nsems may
     be specified as 0.

RETURN VALUES

     The semget() system call returns the id of a semaphore set if successful; otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

     The semget() system call will fail if:

     [EACCES]		Access permission failure.

     [EEXIST]		IPC_CREAT and IPC_EXCL were specified, and a semaphore set corresponding to key already exists.

     [EINVAL]		The number of semaphores requested exceeds the system imposed maximum per set.

     [ENOSPC]		Insufficiently many semaphores are available.

     [ENOSPC]		The kernel could not allocate a struct semid_ds.

     [ENOENT]		No semaphore set was found corresponding to key, and IPC_CREAT was not specified.

SEE ALSO

     semctl(2), semop(2), ftok(3)

BSD
								September 12, 1995							       BSD

semget(2)							System Calls Manual							 semget(2)

Name
       semget - get set of semaphores

Syntax
       #include <sys/types.h>
       #include <sys/ipc.h>
       #include <sys/sem.h>

       int semget (key, nsems, semflg)
       key_t key;
       int nsems, semflg;

Description
       The  system  call  returns the semaphore identifier associated with key.  A semaphore identifier and associated data structure and set con-
       taining nsems semaphores are created for key, if one of the following is true:

       o   The key is equal to IPC_PRIVATE

       o   The key does not already have a semaphore identifier associated with it, and (semflg & IPC_CREAT ) is true.

       For further information, see

       Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:

       o   The sem_perm.cuid, sem_perm.uid, sem_perm.cgid and sem_perm.gid are set equal to the effective user ID and effective group ID,  respec-
	   tively, of the calling process.

       o   The low-order nine bits of sem_perm.mode are set equal to the low-order nine bits of semflg.

       o   The sem_nsems is set equal to the value of nsems.

       o   The sem_otime is set equal to zero (0) and sem_ctime is set equal to the current time.

Return Values
       Upon  successful  completion,  a nonnegative integer, namely a semaphore identifier, is returned.  Otherwise, a value of -1 is returned and
       errno is set to indicate the error.

Diagnostics
       The semget system call fails if any of the following is true:

       [EINVAL]       The nsems is either less than or equal to zero or greater than the system-imposed limit

       [EACCES]       A semaphore identifier exists for key, but operation permission, as specified by the low-order nine bits of semflg would not
		      be granted.  For further information, see

       [EINVAL]       A  semaphore  identifier	exists	for key, but the number of semaphores in the set associated with it is less than nsems and
		      nsems is not equal to zero.

       [ENOENT]       A semaphore identifier does not exist for key and (semflg & IPC_CREAT ) is false.

       [ENOSPC]       A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphore  identifiers
		      in the system would be exceeded.

       [EEXIST]       A semaphore identifier exists for key but ((semflg & IPC_CREAT ) & (semflg & IPC_EXCL )) is true.

See Also
       semctl(2), semop(2), ftok(3)

																	 semget(2)