NAME [Toc] [Back]
mq_receive - receive a message from a message queue
SYNOPSIS [Toc] [Back]
ssize_t mq_receive(mqd_t mqdes,
unsigned int *msg_prio
DESCRIPTION [Toc] [Back]
The mq_receive() system call receives the oldest of the highest
priority message from the message queue specified by mqdes. The
selected message is removed from the queue and copied to the buffer
pointed to by the msg_ptr argument. The argument, msg_len, specifies
the size of the buffer in bytes. The value of msg_len should be
greater than or equal to the mq_msgsize attribute of the message
queue, or mq_receive() will fail.
If the argument msg_prio is not NULL, the priority of the message
removed from the queue is stored in the location pointed to by
If the specified message queue is empty and the O_NONBLOCK flag is not
set in the message queue blocking status associated with mqdes,
mq_receive() will block in priority order, until it can receive a
message from the queue, or until mq_receive() is interrupted by a
signal. If the specified message queue is empty and the O_NONBLOCK
flag is set in the message queue blocking status associated with
mqdes, mq_receive() will not wait for a message to arrive on the queue
and will return with an error.
To use this function, link in the realtime library by specifying -lrt
on the compiler or linker command line.
RETURN VALUE [Toc] [Back]
mq_receive() returns the following values:
n Successful completion. n is the size of the selected
message in bytes and the message is removed from the queue.
-1 Failure. errno is set to indicate the error and no message
is removed from the queue.
ERRORS [Toc] [Back]
If mq_receive() fails, errno is set to one of the following values:
[EAGAIN] The O_NONBLOCK flag is set in the message queue
blocking status associated with mqdes, and the
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message queue is empty.
[EBADF] mqdes is not a valid message queue descriptor open
[EINTR] A signal interrupted the call to mq_receive().
[EINVAL] msg_ptr points to an invalid address.
[EMSGSIZE] The specified message buffer size, msg_len, is
less than the message size attribute of the
[ENOSYS] mq_receive() is not supported by the
SEE ALSO [Toc] [Back]
STANDARDS CONFORMANCE [Toc] [Back]
mq_receive(): POSIX 1003.1b
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