shmget - get an XSI shared memory segment
int shmget(key_t key, size_t size, int
The shmget() function operates on XSI shared memory (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.340, Shared Memory Object). It is unspecified whether this function interoperates with the realtime interprocess communication facilities defined in Realtime .
The shmget() function shall return the shared memory identifier associated with key.
A shared memory identifier, associated data structure, and shared memory segment of at least size bytes (see <sys/shm.h>) are created for key if one of the following is true:
The argument key is equal to IPC_PRIVATE.
The argument key does not already have a shared memory identifier associated with it and (shmflg &IPC_CREAT) is non-zero.
Upon creation, the data structure associated with the new shared memory identifier shall be initialized as follows:
The values of shm_perm.cuid, shm_perm.uid, shm_perm.cgid, and shm_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.
The low-order nine bits of shm_perm.mode are set equal to the low-order nine bits of shmflg.
The value of shm_segsz is set equal to the value of size.
The values of shm_lpid, shm_nattch, shm_atime, and shm_dtime are set equal to 0.
The value of shm_ctime is set equal to the current time.
When the shared memory segment is created, it shall be initialized with all zero values.
Upon successful completion, shmget() shall return a non-negative integer, namely a shared memory identifier; otherwise, it shall return -1 and set errno to indicate the error.
The shmget() function shall fail if:
The following sections are informative.
The POSIX Realtime Extension defines alternative interfaces for interprocess communication. Application developers who need to use IPC should design their applications so that modules using the IPC routines described in XSI Interprocess Communication can be easily modified to use the alternative interfaces.
XSI Interprocess Communication , Realtime , shmat() , shmctl() , shmdt() , shm_open() , shm_unlink() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/shm.h>
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