mq_receive.2 (2010 09)

mq_receive(2) mq_receive(2)

NAME

mq_receive - receive a message from a message queue

SYNOPSIS

#include <sys/mqueue.h>

ssize_t mq_receive(mqd_t mqdes,

char *msg_ptr,

size_t msg_len,

unsigned int *msg_prio

);

DESCRIPTION

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 msg_prio .

If the speciﬁed message queue is empty and the

O_NONBLOCK ﬂag is not set in the message queue block-

ing status associated with mqdes, mq_receive() will block in priority order, until it can receive a mes-

sage 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

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

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 message queue is empty.

[EBADF] mqdes is not a valid message queue descriptor open for reading.

[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 message queue.

[ENOSYS]

mq_receive() is not supported by the implementation.

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mq_receive(2) mq_receive(2) NAME mq_receive - receive a message from a message queue SYNOPSIS #include ssize_t mq_receive(mqd_t char size_t unsigned int ); mqdes, *msg_ptr, msg_len, *msg_prio DESCRIPTION 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.
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(Notes) A (Notes) mA 2 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010