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Posix queues

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Operating Systems BSD Posix queues
# 8  
Old 10-30-2005
Quote:
Originally Posted by Perderabo
Great! So that man page I linked should enable you to read about them. And that page links to the other system calls.
Hi! I was wrong about msgget, it's SYSTEM V queues. POSIX queues is mq_open in <posix4/mqueue.h> and I got error: "undefined reference to 'mq_open' "
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LEARN ABOUT NETBSD

msgget

MSGGET(2)						      BSD System Calls Manual							 MSGGET(2)

NAME

     msgget -- get message queue identifier

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/msg.h>

     int
     msgget(key_t key, int msgflg);

DESCRIPTION

     The msgget() system call 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 both the IPC_CREAT bit and the IPC_EXCL bit are set in msgflg, and key has a message queue identifier
     associated with it already, the operation will fail.

     If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows:

     o	 msg_perm.cuid and msg_perm.uid are set to the effective uid of the calling process.

     o	 msg_perm.gid and msg_perm.cgid are set to the effective gid of the calling process.

     o	 msg_perm.mode is set to the lower 9 bits of msgflg.

     o	 msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0.

     o	 msg_qbytes is set to the system wide maximum value for the number of bytes in a queue (MSGMNB).

     o	 msg_ctime is set to the current time.

RETURN VALUES

     Upon successful completion a positive message queue identifier is returned.  Otherwise, -1 is returned and the global variable errno is set
     to indicate the error.

ERRORS

     [EACCES]		A message queue is already associated with key and the caller has no permission to access it.

     [EEXIST]		Both IPC_CREAT and IPC_EXCL are set in msgflg, and a message queue is already associated with key.

     [ENOSPC]		A new message queue could not be created because the system limit for the number of message queues has been reached.

     [ENOENT]		IPC_CREAT is not set in msgflg and no message queue associated with key was found.

SEE ALSO

     msgctl(2), msgrcv(2), msgsnd(2), ftok(3)

STANDARDS

     The msgget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').

HISTORY

     Message queues appeared in the first release of AT&T System V UNIX.

BSD
								   May 13, 2004 							       BSD