| MSGSND(2) | System Calls Manual | MSGSND(2) |
msgsnd —
#include <sys/msg.h>
int
msgsnd(int
msqid, const void
*msgp, size_t
msgsz, int
msgflg);
msgsnd() function sends a message from the message
queue specified in msqid. The msgp
argument is a pointer to a user-defined structure containing the message. This
structure must contain a first field of type long that
will indicate the user-defined type of the message. The remaining fields will
contain the contents of the message. The following is an example of what this
user-defined structure might look like:
struct mymsg {
long mtype; /* message type */
char mtext[1]; /* body of message */
};
The mtype field is an integer greater than 0
that can be used for selecting messages (see
msgrcv(2)). The
mtext field is an array of bytes of length
msgsz, with size up to the system limit
MSGMAX.
If the number of bytes already on the message queue plus
msgsz is greater than the maximum number of bytes in
the message queue (msg_qbytes, see
msgctl(2)), or if the number
of messages on all queues system-wide is already equal to the system limit,
msgflg determines the action of
msgsnd(). If msgflg has
IPC_NOWAIT mask set in it, the call will return
immediately. If msgflg does not have
IPC_NOWAIT set in it, the call will block until:
EINVAL.EINTR.After a successful call, the data structure associated with the message queue is updated in the following way:
msgsnd() will fail if:
EACCES]EAGAIN]IPC_NOWAIT was set in
msgflg.EFAULT]EINTR]EINVAL]The message queue was removed while
msgsnd() was waiting for a resource to become
available in order to deliver the message.
The msgsz argument is greater than
msg_qbytes or
SSIZE_MAX.
msgsnd system call conforms to
X/Open System Interfaces and Headers Issue 5
(“XSH5”) and IEEE Std 1003.1-2001
(“POSIX.1”).
| July 24, 2013 | NetBSD 9.4 |