_POSIX_MESSAGE_PASSING

POSIX Message Passing option (feature-test macro). More...

Files
file	mqueue.h
	POSIX message queues (<mqueue.h>)

Typedefs
typedef int	mqd_t
	Message queue descriptor returned by mq_open().

Functions
mqd_t	mq_open (const char *name, int oflags,...)
	Open or create a message queue.
int	mq_close (mqd_t mqdes)
	Close a message queue descriptor.
int	mq_unlink (const char *name)
	Remove a named message queue.
int	mq_getattr (mqd_t mqdes, struct mq_attr *mqstat)
	Get the attributes of a message queue.
ssize_t	mq_receive (mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned int *msg_prio)
	Receive the oldest highest-priority message from a queue.
int	mq_send (mqd_t mqdes, const char *msg_ptr, size_t msg_len, unsigned int msg_prio)
	Add a message to a queue.
int	mq_setattr (mqd_t mqdes, const struct mq_attr *mqstat, struct mq_attr *omqstat)
	Set the attributes of a message queue.
ssize_t	mq_timedreceive (mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned int *msg_prio, const struct timespec *abstime)
	Receive a message from a queue with an absolute timeout.
int	mq_timedsend (mqd_t mqdes, const char *msg_ptr, size_t msg_len, unsigned int msg_prio, const struct timespec *abstime)
	Send a message to a queue with an absolute timeout.
int	mq_notify (mqd_t mqdes, const struct sigevent *notification)
	Register for notification when a message arrives on an empty queue.

Detailed Description

POSIX Message Passing option (feature-test macro).

When defined, indicates that message queue support is available. The mq_*() APIs are documented under this option.

Typedef Documentation

mqd_t

typedef int mqd_t

Message queue descriptor returned by mq_open().

A message queue descriptor is a file descriptor; the access mode and O_NONBLOCK are per-descriptor state, as for any other open file description.

Definition at line 40 of file mqueue.h.

Function Documentation

mq_close()

int mq_close

(

mqd_t

mqdes

)

Close a message queue descriptor.

Parameters

mqdes

Message queue descriptor.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_close.html

mq_getattr()

int mq_getattr	(	mqd_t	mqdes,
		struct mq_attr *	mqstat
	)

Get the attributes of a message queue.

Parameters

mqdes	Message queue descriptor.
mqstat	Output: current attributes.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_getattr.html

mq_notify()

int mq_notify	(	mqd_t	mqdes,
		const struct sigevent *	notification
	)

Register for notification when a message arrives on an empty queue.

Parameters

mqdes	Message queue descriptor.
notification	Notification specification, or NULL to cancel.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_notify.html

mq_open()

mqd_t mq_open	(	const char *	name,
		int	oflags,
			...
	)

Open or create a message queue.

Parameters

name	Queue name (must start with '/').
oflags	Open flags (O_RDONLY, O_WRONLY, O_RDWR, O_CREAT, O_EXCL, O_NONBLOCK).
...	If O_CREAT: mode_t mode, struct mq_attr *attr.

Returns

Message queue descriptor on success, or (mqd_t)-1 on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_open.html

mq_receive()

ssize_t mq_receive	(	mqd_t	mqdes,
		char *	msg_ptr,
		size_t	msg_len,
		unsigned int *	msg_prio
	)

Receive the oldest highest-priority message from a queue.

Parameters

mqdes	Message queue descriptor (opened with O_RDONLY or O_RDWR).
msg_ptr	Buffer to receive the message.
msg_len	Size of msg_ptr (must be >= mq_msgsize).
msg_prio	Output: priority of the received message, or NULL.

Returns

Number of bytes in the received message on success, or -1 on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_receive.html

mq_send()

int mq_send	(	mqd_t	mqdes,
		const char *	msg_ptr,
		size_t	msg_len,
		unsigned int	msg_prio
	)

Add a message to a queue.

Parameters

mqdes	Message queue descriptor (opened with O_WRONLY or O_RDWR).
msg_ptr	Message to send.
msg_len	Size of the message in bytes.
msg_prio	Priority of the message (higher value = higher priority).

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_send.html

mq_setattr()

int mq_setattr	(	mqd_t	mqdes,
		const struct mq_attr *	mqstat,
		struct mq_attr *	omqstat
	)

Set the attributes of a message queue.

Parameters

mqdes	Message queue descriptor.
mqstat	New attributes (only mq_flags is used).
omqstat	Output: previous attributes, or NULL.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_setattr.html

mq_timedreceive()

ssize_t mq_timedreceive	(	mqd_t	mqdes,
		char *	msg_ptr,
		size_t	msg_len,
		unsigned int *	msg_prio,
		const struct timespec *	abstime
	)

Receive a message from a queue with an absolute timeout.

Parameters

mqdes	Message queue descriptor.
msg_ptr	Buffer to receive the message.
msg_len	Size of msg_ptr.
msg_prio	Output: message priority, or NULL.
abstime	Absolute timeout (CLOCK_REALTIME).

Returns

Number of bytes in the message on success, or -1 on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_timedreceive.html

mq_timedsend()

int mq_timedsend	(	mqd_t	mqdes,
		const char *	msg_ptr,
		size_t	msg_len,
		unsigned int	msg_prio,
		const struct timespec *	abstime
	)

Send a message to a queue with an absolute timeout.

Parameters

mqdes	Message queue descriptor.
msg_ptr	Message to send.
msg_len	Size of the message in bytes.
msg_prio	Priority of the message.
abstime	Absolute timeout (CLOCK_REALTIME).

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_timedsend.html

mq_unlink()

int mq_unlink

(

const char *

name

)

Remove a named message queue.

Parameters

name	Queue name.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_unlink.html