mq_send

Langue: en

Version: DECEMBER 2002 (mandriva - 01/05/08)

Autres sections - même nom

Section: 2 (Appels système)

NAME

mq_send - send a message to a message queue

SYNOPSIS

gcc [ flag... ] file ... -lmqueue [ library... ]

#include <mqueue.h> #include <time.h>

int mq_send(mqd_t mqdes, const char *msg_ptr, size_t msg_len, unsigned int msg_prio);

int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len, unsigned msg_prio,const struct timespec *abs_timeout);

DESCRIPTION

The mq_send() function adds the message pointed to by the argument msg_ptr to the message queue specified by mqdes. The msg_len argument specifies the length of the message in bytes pointed to by msg_ptr. The value of msg_len is less than or equal to the mq_msgsize attribute of the message queue, or mq_send() fails.

If the specified message queue is not full, mq_send() behaves as if the message is inserted into the message queue at the position indicated by the msg_prio argument. A message with a larger numeric value of msg_prio is inserted before messages with lower values of msg_prio. A message will be inserted after other messages in the queue, if any, with equal msg_prio. The value of msg_prio must be less than MQ_PRIO_MAX.

If the specified message queue is full and O_NONBLOCK is not set in the message queue description associated with mqdes (see mq_open(2) and mq_setattr(2)), mq_send() blocks until space becomes available to enqueue the message, or until mq_send() is interrupted by a signal. If more than one thread is waiting to send when space becomes available in the message queue, then the thread of the highest priority which has been waiting the longest is unblocked to send its message. If the specified message queue is full and O_NONBLOCK is set in the message queue description associated with mqdes, the message is not queued and mq_send() returns an error.

The mq_timedsend() function adds a message to the message queue specified by mqdes in the manner defined for the mq_send() function. However, if the specified message queue is full and O_NONBLOCK is not set in the message queue description associated with mqdes, the wait for sufficient room in the queue is terminated when the specified timeout expires. The timeout is given as absolute value. If there is a (common) need to use relative timeout i.e. to wait for some time specified from the time of mq_timedsend() invocation then abs_timeout fields must be the sum of current time and the relative timeout. If O_NONBLOCK is set in the message queue description, this function is equivalent to mq_send().

RETURN VALUES

Upon successful completion, mq_send() and mq_timedsend() returns 0; otherwise, the function returns -1 and sets errno to indicate the error condition.

DIAGNOSTICS

The mq_send() function will fail if:
EAGAIN
The O_NONBLOCK flag is set in the message queue description associated with mqdes, and the specified message queue is full.
EBADF
The mqdes argument is not a valid message queue descriptor open for writing.
EINTR
A signal interrupted the call to mq_send().
EINVAL
The value of msg_prio was outside the valid range or msg_ptr is NULL.
EMSGSIZE
The specified message length, msg_len, exceeds the message size attribute of the message queue.
ENOMEM
Kernel failed to allocate necessary memory.
EINVAL
The process or thread would have blocked, and the abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.
ETIMEDOUT
The O_NONBLOCK flag was not set when the message queue was opened, but the timeout expired before the message could be added to the queue.
EFAULT
msg_ptr or abs_timeout points outside your accessible address space.

AUTHORS

Michal Wronski <wrona@mat.uni.torun.pl>
Krzysztof Benedyczak <golbi@mat.uni.torun.pl>

CONFORMING TO

IEEE Std 1003.1-2001

SEE ALSO

mq_open(2), mq_receive(2)