Originální popis anglicky:
mq_send, mq_timedsend - send a message to a message queue (
REALTIME)
Návod, kniha: POSIX Programmer's Manual
#include <mqueue.h>
int mq_send(mqd_t
mqdes, const char
*msg_ptr , size_t
msg_len,
unsigned
msg_prio );
#include <mqueue.h>
#include <time.h>
int mq_timedsend(mqd_t
mqdes, const char
*msg_ptr, size_t
msg_len,
unsigned
msg_prio , const struct timespec
*abs_timeout );
The
mq_send() function shall add 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 shall be less than or equal
to the
mq_msgsize attribute of the message queue, or
mq_send()
shall fail.
If the specified message queue is not full,
mq_send() shall behave 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 shall be inserted before messages with lower values of
msg_prio. A message shall be inserted after other messages in the
queue, if any, with equal
msg_prio. The value of
msg_prio shall
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,
mq_send() shall block
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 and the
Priority Scheduling option is supported, then the thread of the highest
priority that has been waiting the longest shall be unblocked to send its
message. Otherwise, it is unspecified which waiting thread is unblocked. If
the specified message queue is full and O_NONBLOCK is set in the message queue
description associated with
mqdes, the message shall not be queued and
mq_send() shall return an error.
The
mq_timedsend() function shall add 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 shall be terminated when the specified
timeout expires. If O_NONBLOCK is set in the message queue description, this
function shall be equivalent to
mq_send().
The timeout shall expire when the absolute time specified by
abs_timeout
passes, as measured by the clock on which timeouts are based (that is, when
the value of that clock equals or exceeds
abs_timeout), or if the
absolute time specified by
abs_timeout has already been passed at the
time of the call.
If the Timers option is supported, the timeout shall be based on the
CLOCK_REALTIME clock; if the Timers option is not supported, the timeout shall
be based on the system clock as returned by the
time() function.
The resolution of the timeout shall be the resolution of the clock on which it
is based. The
timespec argument is defined in the
<time.h>
header.
Under no circumstance shall the operation fail with a timeout if there is
sufficient room in the queue to add the message immediately. The validity of
the
abs_timeout parameter need not be checked when there is sufficient
room in the queue.
Upon successful completion, the
mq_send() and
mq_timedsend() functions shall return a value of zero. Otherwise, no
message shall be enqueued, the functions shall return -1, and
errno
shall be set to indicate the error.
The
mq_send() and
mq_timedsend() functions shall 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()
or mq_timedsend().
- EINVAL
- The value of msg_prio was outside the valid
range.
- 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.
- EMSGSIZE
- The specified message length, msg_len, exceeds the
message size attribute of the message queue.
- 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.
The following sections are informative.
None.
The value of the symbol {MQ_PRIO_MAX} limits the number of priority levels
supported by the application. Message priorities range from 0 to
{MQ_PRIO_MAX}-1.
None.
None.
mq_open() ,
mq_receive() ,
mq_setattr() ,
mq_timedreceive() ,
time() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<mqueue.h>,
<time.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
