NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | USAGE | SEE ALSO
#include <sys/msg.h>int msgget(key_t key, int msgflg);
The msgget() argument returns the message queue identifier associated with key.
A message queue identifier and associated message queue and data structure (see intro(2)) are created for key if one of the following are true:
key is IPC_PRIVATE.
key does not already have a message queue identifier associated with it, and (msgflg&IPC_CREAT) is true.
On creation, the data structure associated with the new message queue identifier is initialized as follows:
msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set to the effective user ID and effective group ID, respectively, of the calling process.
The low-order 9 bits of msg_perm.mode are set to the low-order 9 bits of msgflg.
msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set to 0.
msg_ctime is set to the current time.
msg_qbytes is set to the system limit.
Upon successful completion, a non-negative integer representing a message queue identifier is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The msgget() function will fail if:
A message queue identifier exists for key, but operation permission (see intro(2)) as specified by the low-order 9 bits of msgflg would not be granted.
A message queue identifier exists for key but (msgflg&IPC_CREAT) and (msgflg&IPC_EXCL) are both true.
A message queue identifier does not exist for key and (msgflg&IPC_CREAT) is false.
A message queue identifier is to be created but the system-imposed limit on the maximum number of allowed message queue identifiers system wide would be exceeded.
When a UFS file system is mounted with logging enabled, file system transactions that free blocks from files might not actually add those freed blocks to the file system's free list until some unspecified time in the future. This behavior improves file system performance but does not conform to the POSIX, Single UNIX Specification, SPARC Conformance Definition, System V Application Binary Interface, System V Interface Definition, and X/Open Portability Guide Standards, which require that freed space be available immediately. To enable standards conformance regarding file deletions or to address the problem of not being able to grow files on a relatively full UFS file system even after files have been deleted, disable UFS logging (see mount_ufs(1M).
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | USAGE | SEE ALSO