mq_send, mq_timedsend — send a message to a message queue
#include <mqueue.h>
mqd_t
mq_send( |
mqd_t | mqdes, |
const char * | msg_ptr, | |
size_t | msg_len, | |
unsigned | msg_prio) ; |
#define _XOPEN_SOURCE 600 #include <time.h> #include <mqueue.h>
mqd_t
mq_timedsend( |
mqd_t | mqdes, |
const char * | msg_ptr, | |
size_t | msg_len, | |
unsigned | msg_prio, | |
const struct timespec * | abs_timeout) ; |
mq_send
() adds the message
pointed to by msg_ptr
to the message queue referred to by the descriptor mqdes
. The msg_len
argument specifies the
length of the message pointed to by msg_ptr
; this length must be
less than or equal to the queue's mq_msgsize
attribute.
Zero-length messages are allowed.
The msg_prio
argument is a non-negative 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_maxmsg
attribute), 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_NONBLOCK
flag
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_NONBLOCK
flag is not enabled for the
message queue description, then abs_timeout
points to a
structure which specifies a ceiling on the time for which the
call will block. This ceiling is an absolute timeout in
seconds and nanoseconds since the Epoch (midnight on the
morning of 1 January 1970), 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.
On success, mq_send
() and
mq_timedsend
() return zero; on
error, −1 is returned, with errno
set to indicate the error.
The queue was empty, and the O_NONBLOCK
flag was set for the
message queue description referred to by mqdes
.
The descriptor specified in mqdes
was invalid.
msg_len
was
greater than the mq_msgsize
attribute of
the message queue.
The call was interrupted by a signal handler.
The call would have blocked, and abs_timeout
was invalid,
either because tv_sec
was less than
zero, or because tv_nsec
was less than
zero or greater than 1000 million.
The call timed out before a message could be transferred.
mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_receive(3), mq_unlink(3), feature_test_macros(7), mq_overview(7)
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