The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

#### NAME

> mqueue.h - message queues (REALTIME)

#### SYNOPSIS

> `[MSG] #include <mqueue.h>`

#### DESCRIPTION

> The <mqueue.h> header shall define the mqd_t type, which is used for message queue descriptors. This is not an array type.

> The <mqueue.h> header shall define the pthread_attr_t, size_t, and ssize_t types as described in <sys/types.h>.

> The <mqueue.h> header shall define the struct timespec structure as described in <time.h>.

> The tag sigevent shall be declared as naming an incomplete structure type, the contents of which are described in the <signal.h> header.

> The <mqueue.h> header shall define the mq_attr structure, which is used in getting and setting the attributes of a message queue. Attributes are initially set when the message queue is created. An mq_attr structure shall have at least the following fields:

>     long    mq_flags    Message queue flags.
>     long    mq_maxmsg   Maximum number of messages.
>     long    mq_msgsize  Maximum message size.
>     long    mq_curmsgs  Number of messages currently queued.

> The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

>     int      mq_close(mqd_t);
>     int      mq_getattr(mqd_t, struct mq_attr *);
>     int      mq_notify(mqd_t, const struct sigevent *);
>     mqd_t    mq_open(const char *, int, ...);
>     ssize_t  mq_receive(mqd_t, char *, size_t, unsigned *);
>     int      mq_send(mqd_t, const char *, size_t, unsigned);
>     int      mq_setattr(mqd_t, const struct mq_attr *restrict,
>                  struct mq_attr *restrict);
>     ssize_t  mq_timedreceive(mqd_t, char *restrict, size_t,
>                  unsigned *restrict, const struct timespec *restrict);
>     int      mq_timedsend(mqd_t, const char *, size_t, unsigned,
>                  const struct timespec *);
>     int      mq_unlink(const char *);

> Inclusion of the <mqueue.h> header may make visible symbols defined in the headers <fcntl.h>, <signal.h>, and <time.h>.

The following sections are informative.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> <fcntl.h>, <signal.h> , <sys/types.h>, <time.h>

> XSH mq_close, mq_getattr, mq_notify, mq_open, mq_receive, mq_send, mq_setattr, mq_unlink

#### CHANGE HISTORY

> First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

#### Issue 6

> The <mqueue.h> header is marked as part of the Message Passing option.

> The mq_timedreceive() and mq_timedsend() functions are added for alignment with IEEE Std 1003.1d-1999.

> The restrict keyword is added to the prototypes for mq_setattr() and mq_timedreceive().

#### Issue 7

> Type and structure declarations are added.

End of informative text.

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