The msgget function returns the message queue identifier associated with key. A message queue identifier is a unique integer greater than zero.
A message queue is created if either key is equal to IPC_PRIVATE, or key does not have a message queue identifier associated with it, and the IPC_CREAT bit is set in msgflg.
If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(3)) is initialized as follows:
- msg_perm.cuid and msg_perm.uid are set to the effective uid of the calling process.
- msg_perm.gid and msg_perm.cgid are set to the effective gid of the calling process.
- msg_perm.mode is set to the lower 9 bits of msgflg.
- msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0.
- msg_qbytes is set to the system wide maximum value for the number of bytes in a queue ( MSGMNB).
- msg_ctime is set to the current time.