Copyright (c) 1995 David Hovemeyer <firstname.lastname@example.org> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the d...
NAMEsemget - obtain a semaphore id
SYNOPSISIn sys/types.h In sys/ipc.h In sys/sem.h Ft int Fn semget key_t key int nsems int flag
DESCRIPTIONBased on the values of Fa key and Fa flag , Fn 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:
- IPC_PRIVATE may be specified, in which case a new IPC object will be created.
- An integer constant may be specified. If no IPC object corresponding to Fa key is specified and the IPC_CREAT bit is set in Fa flag , a new one will be created.
- 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 Fa flag argument:
- Read access for user.
- 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, Fa nsems is used to indicate the number of semaphores the set should contain. Otherwise, Fa nsems may be specified as 0.
RETURN VALUESThe Fn semget system call returns the id of a semaphore set if successful; otherwise, -1 is returned and errno is set to indicate the error.
ERRORSThe Fn semget system call will fail if:
- Bq Er EACCES
- Access permission failure.
- Bq Er EEXIST
- IPC_CREAT and IPC_EXCL were specified, and a semaphore set corresponding to Fa key already exists.
- Bq Er EINVAL
- The number of semaphores requested exceeds the system imposed maximum per set.
- Bq Er ENOSPC
- Insufficiently many semaphores are available.
- Bq Er ENOSPC
- The kernel could not allocate a Fa struct semid_ds .
- Bq Er ENOENT
- No semaphore set was found corresponding to Fa key , and IPC_CREAT was not specified.