Manpage of MQ_SEND

MQ_SEND

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

mq_send, mq_timedsend - send a message to a message queue  

SYNOPSIS

#include <mqueue.h>int mq_send(mqd_t mqdes, const char *msg_ptr,              size_t msg_len, unsigned int msg_prio);#include <time.h>#include <mqueue.h>int mq_timedsend(mqd_t mqdes, const char *msg_ptr,              size_t msg_len, unsigned int msg_prio,              const struct timespec *abs_timeout);

Link with -lrt.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

mq_timedsend():

_POSIX_C_SOURCE >= 200112L
 

DESCRIPTION

mq_send() adds the message pointed to by msg_ptrto the message queue referred to by the message queue descriptor mqdes. The msg_lenargument specifies the length of the message pointed to by msg_ptr; this length must be less than or equal to the queue's mq_msgsizeattribute. Zero-length messages are allowed.

The msg_prioargument is a nonnegative integer that specifies the priority of this message. Messages are placed on the queue in decreasing order of priority, with newer messages of the same priority being placed after older messages with the same priority.

If the message queue is already full (i.e., the number of messages on the queue equals the queue's mq_maxmsgattribute), then, by default, mq_send() blocks until sufficient space becomes available to allow the message to be queued, or until the call is interrupted by a signal handler. If the O_NONBLOCKflag is enabled for the message queue description, then the call instead fails immediately with the error EAGAIN.

mq_timedsend() behaves just like mq_send(), except that if the queue is full and the O_NONBLOCKflag is not enabled for the message queue description, then abs_timeoutpoints to a structure which specifies how long the call will block. This value is an absolute timeout in seconds and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), specified in the following structure:

struct timespec {
    time_t tv_sec;        /* seconds */
    long   tv_nsec;       /* nanoseconds */
};

If the message queue is full, and the timeout has already expired by the time of the call, mq_timedsend() returns immediately.  

RETURN VALUE

On success, mq_send() and mq_timedsend() return zero; on error, -1 is returned, with errnoset to indicate the error.  

ERRORS

EAGAIN
The queue was full, and the O_NONBLOCKflag was set for the message queue description referred to by mqdes.
EBADF
The file descriptor specified in mqdeswas invalid.
EINTR
The call was interrupted by a signal handler; see signal(7).
EINVAL
The call would have blocked, and abs_timeoutwas invalid, either because tv_secwas less than zero, or because tv_nsecwas less than zero or greater than 1000 million.
EMSGSIZE
msg_lenwas greater than the mq_msgsizeattribute of the message queue.
ETIMEDOUT
The call timed out before a message could be transferred.
 

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
mq_send(), mq_timedsend() Thread safetyMT-Safe
 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.  

NOTES

On Linux, mq_timedsend() is a system call, and mq_send() is a library function layered on top of that system call.  

SEE ALSO

mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_receive(3), mq_unlink(3), mq_overview(7), time(7)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
NOTES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 22:27:53 GMT, June 20, 2016