mq_receive - Receives the oldest, highest-priority message
from the message queue (P1003.1b)
ssize_t mq_receive ( mqd_t mqdes, char *msg_ptr, size_t
msg_len, unsigned int *msg_prio);
Realtime Library (librt.so, librt.a)
Specifies a message queue by descriptor. Specifies a
pointer to a buffer 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
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 interrupted 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.
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 mq_receive function fails under the following conditions:
O_NONBLOCK 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 virtual 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.
Guide to Realtime Programming
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