Manual page for mq_receive(3R)
mq_receive - receive a message from a message queue
SYNOPSIS
cc
[ flag ... ] file ...
-lposix4
[ library ... ]
#include <mqueue.h>
ssize_t mq_receive(mqd_t mqdes, char *msg_ptr,
size_t msg_len,
unsigned int msg_prio);
struct mq_attr {
long mq_flags; /* message queue flags */
long mq_maxmsg; /* maximum number of messages */
long mq_msgsize; /* maximum message size */
long mq_curmsgs; /* number of messages currently queued */
...
};
MT-LEVEL
MT-Safe
DESCRIPTION
mq_receive()
is used to
receive the oldest of the highest priority message(s)
from the message queue specified by
mqdes.
If the size of the buffer in bytes, specified by
msg_len,
is less than the
mq_msgsize
attribute of the message queue, the function fails and returns an error.
Otherwise, the selected message is removed from the queue
and copied to the buffer pointed to by
msg_ptr.
If
msg_prio
is not NULL, the priority of the selected message is stored
in the location referenced by
msg_prio.
If the specified message queue is empty and O_NONBLOCK
is not set in the message queue description associated with
mqdes,
(see
mq_open.3r
and
mq_setattr.3r
mq_receive()
blocks, waiting until a message is enqueued on the message queue,
or until
mq_receive()
is interrupted by a signal.
If more than one process (or thread) is waiting to receive a message when a
message arrives at an empty queue,
then the process of highest priority that has been waiting the longest
is selected to receive the message.
If the specified message queue is empty and O_NONBLOCK
is set in the message queue description associated with
mqdes,
no message is removed from the queue, and
mq_receive()
returns an error.
RETURN VALUES
Upon successful completion,
mq_receive()
returns the length of the selected message in bytes
and the message will have been removed from the queue.
Otherwise, no message is removed from the queue,
the function returns a value of
-1,
and sets
errno
to indicate the error condition.
ERRORS
- EAGAIN
-
O_NONBLOCK was set in the message description associated with
mqdes,
and the specified message queue is empty.
- EBADF
-
mqdes
is not a valid message queue descriptor open for reading.
- EMSGSIZE
-
msg_len
is less than the message size attribute of the message queue.
- EINTR
-
mq_receive()
operation was interrupted by a signal.
- ENOSYS
-
mq_receive()
is not supported by this implementation.
SEE ALSO
mq_open.3r
mq_send.3r
mq_setattr.3r
BUGS
In Solaris 2.5, these functions always return -1 and set
errno
to
ENOSYS,
because this release does not support the
Message Passing option.
It is our intention to provide support
for these interfaces in future releases.
Created by unroff & hp-tools.
© by Hans-Peter Bischof. All Rights Reserved (1997).
Last modified 21/April/97
