mq_send , mq_timedsend
- send a message to message queue (REALTIME)
LIBRARY
Lb librt
SYNOPSIS
#include <mqueue.h> int
Fo mq_send
Fa mqd_t mqdes
Fa const char *msg_ptr
Fa size_t msg_len
Fa unsigned msg_prio
Fc Ft int
Fo mq_timedsend
Fa mqd_t mqdes
Fa const char *msg_ptr
Fa size_t msg_len
Fa unsigned msg_prio
Fa const struct timespec *abs_timeout
Fc
DESCRIPTION
The
mq_send ();
system call adds the message pointed to by the argument
Fa msg_ptr
to the message queue specified by
Fa mqdes .
The
Fa msg_len
argument specifies the length of the message, in bytes, pointed to by
Fa msg_ptr .
The value of
Fa msg_len
should be less than or equal to the
mq_msgsize
attribute of the message queue, or
mq_send ();
will fail.
If the specified message queue is not full,
mq_send ();
will behave as if the message is inserted into the message queue at
the position indicated by the
Fa msg_prio
argument.
A message with a larger numeric value of
Fa msg_prio
will be inserted before messages with lower values of
Fa msg_prio .
A message will be inserted after other messages in the queue, if any,
with equal
Fa msg_prio .
The value of
Fa msg_prio
should be less than
Br q Dv MQ_PRIO_MAX .
If the specified message queue is full and
O_NONBLOCK
is not set in the message queue description associated with
Fa mqdes ,
mq_send ();
will 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 will 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
Fa mqdes ,
the message will not be queued and
mq_send ();
will return an error.
The
mq_timedsend ();
system call will add a message to the message queue specified by
Fa mqdes
in the manner defined for the
mq_send ();
system call.
However, if the specified message queue is full and
O_NONBLOCK
is not set in the message queue description associated with
Fa mqdes ,
the wait for sufficient room in the queue will be terminated when
the specified timeout expires.
If
O_NONBLOCK
is set in the message queue description, this system call is
equivalent to
mq_send (.);
The timeout will expire when the absolute time specified by
Fa abs_timeout
passes, as measured by the clock on which timeouts are based (that is,
when the value of that clock equals or exceeds
Fa abs_timeout ) ,
or if the absolute time specified by
Fa abs_timeout
has already been passed at the time of the call.
The timeout is based on the
CLOCK_REALTIME
clock.
RETURN VALUES
Upon successful completion, the
mq_send ();
and
mq_timedsend ();
system calls return a value of zero.
Otherwise, no message will be
enqueued, the system calls return -1, and
the global variable
errno
is set to indicate the error.
ERRORS
The
mq_send ();
and
mq_timedsend ();
system calls
will fail if:
Bq Er EAGAIN
The
O_NONBLOCK
flag is set in the message queue description associated with
Fa mqdes ,
and the specified message queue is full.
Bq Er EBADF
The
Fa mqdes
argument is not a valid message queue descriptor open for writing.
Bq Er EINTR
A signal interrupted the call to
mq_send ();
or
mq_timedsend (.);
Bq Er EINVAL
The value of
Fa msg_prio
was outside the valid range.
Bq Er EINVAL
The process or thread would have blocked, and the
Fa abs_timeout
parameter specified a nanoseconds field value less than zero or greater
than or equal to 1000 million.
Bq Er EMSGSIZE
The specified message length,
Fa msg_len ,
exceeds the message size attribute of the message queue.
Bq Er 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
mq_send ();
and
mq_timedsend ();
system calls conform to
St -p1003.1-2004 .
HISTORY
Support for
POSIX
message queues first appeared in
Fx 7.0 .
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2004 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.
