mq_receive(3)mq_receive(3)NAMEmq_receive - Receives the oldest, highest-priority message from the
message queue (P1003.1b)
SYNOPSIS
#include <mqueue.h>
ssize_t mq_receive ( mqd_t mqdes, char *msg_ptr, size_t msg_len,
unsigned int *msg_prio);
LIBRARY
Realtime Library (librt.so, librt.a)
PARAMETERS
Specifies a message queue by descriptor. Specifies a pointer to a buf‐
fer to receive the message. Specifies the size of the receive buffer
identified by the msg_ptr argument. Specifies a pointer to a location
to receive the message priority.
DESCRIPTION
The mq_receive function receives the oldest, highest-priority message
from the message queue. The message is removed from the queue and
transferred to the buffer pointed to by the msg_ptr argument.
If the specified message queue is empty and the O_NONBLOCK option is
not set with the mqdes argument, the mq_receive function blocks until a
message is put on the queue or until the mq_receive function is inter‐
rupted by a signal. If more than one process is waiting to receive a
message when a message arrives at an empty queue, the highest-priority
process that has been waiting the longest is selected to receive the
message. If the message queue is empty and the O_NONBLOCK option is
set, no message is removed from the queue, and an error is returned.
RETURN VALUES
On successful completion, the function returns the length of the
selected message.
Otherwise, the function returns the value -1 and sets errno to indicate
the error. No message is removed from the queue.
ERRORS
The mq_receive function fails under the following conditions: O_NON‐
BLOCK was set in the message description associated with mqdes, and the
specified message queue is empty. The mqdes argument is not a valid
message queue descriptor open for reading. The implementation has
detected a data corruption problem with the message. An internal vir‐
tual memory error occurred. The mq_receive function was interrupted by
a signal. The specified message buffer size, msg_len, is less than the
message size attribute of the message queue.
SEE ALSO
Functions: mq_send(3)
Guide to Realtime Programming
mq_receive(3)
