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mq_receive - Receives the oldest, highest-priority message from the message
ssize_t mq_receive (
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
Specifies a pointer to a location to receive the message priority.
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
Otherwise, the function returns the value -1 and sets errno to indicate the
error. No message is removed from the queue.
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
The implementation has detected a data corruption problem with the
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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