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mqueue.h File Reference

Message queues. More...

Go to the source code of this file.

Data Structures

struct  mq_attr
 Message queue attributes. More...
 

Typedefs

typedef void * mqd_t
 Message queue descriptor.
 

Functions

int mq_close (mqd_t mqdes)
 Close a message queue. More...
 
int mq_getattr (mqd_t mqdes, struct mq_attr *mqstat)
 Get message queue attributes. More...
 
mqd_t mq_open (const char *name, int oflag, mode_t mode, struct mq_attr *attr)
 Open a message queue. More...
 
ssize_t mq_receive (mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned int *msg_prio)
 Receive a message from a message queue. More...
 
int mq_send (mqd_t mqdes, const char *msg_ptr, size_t msg_len, unsigned msg_prio)
 Send a message to a message queue. More...
 
ssize_t mq_timedreceive (mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned *msg_prio, const struct timespec *abstime)
 Receive a message from a message queue with timeout. More...
 
int mq_timedsend (mqd_t mqdes, const char *msg_ptr, size_t msg_len, unsigned msg_prio, const struct timespec *abstime)
 Send a message to a message queue with timeout. More...
 
int mq_unlink (const char *name)
 Remove a message queue. More...
 

Detailed Description

Function Documentation

◆ mq_close()

int mq_close ( mqd_t  mqdes)

Close a message queue.

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

Return values
0- Upon successful completion
-1- A error occurred. errno is also set.
Side Effects Possible errno values

EBADF - The mqdes argument is not a valid message queue descriptor.

◆ mq_getattr()

int mq_getattr ( mqd_t  mqdes,
struct mq_attr mqstat 
)

Get message queue attributes.

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

Return values
0- Upon successful completion
-1- A error occurred. errno is also set.
Side Effects Possible errno values

DBADF - The mqdes argument is not a valid message queue descriptor.

◆ mq_open()

mqd_t mq_open ( const char *  name,
int  oflag,
mode_t  mode,
struct mq_attr attr 
)

Open a message queue.

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

Note
Supported name pattern: leading <slash> character in name is always required; the maximum length (excluding null-terminator) of the name argument can be NAME_MAX. The default value of NAME_MAX in FreeRTOS_POSIX_portable_default.h is 64, which can be overwritten by user.
mode argument is not supported.
Supported oflags: O_RDWR, O_CREAT, O_EXCL, and O_NONBLOCK.
Return values
Messagequeue descriptor – Upon successful completion
(mqd_t)- 1 – An error occurred. errno is also set.
Side Effects Possible errno values

EINVAL - name argument is invalid (not following name pattern), OR if O_CREAT is specified in oflag with attr argument not NULL and either mq_maxmsg or mq_msgsize is equal to or less than zero, OR either O_CREAT or O_EXCL is not set and a queue with the same name is unlinked but pending to be removed.
EEXIST - O_CREAT and O_EXCL are set and the named message queue already exists.
ENOSPC - There is insufficient space for the creation of the new message queue.
ENOENT - O_CREAT is not set and the named message queue does not exist.

◆ mq_receive()

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

Receive a message from a message queue.

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

Note
msg_prio argument is not supported. Messages are not checked for corruption.
Return values
Thelength of the selected message in bytes - Upon successful completion. The message is removed from the queue
-1- An error occurred. errno is also set.
Side Effects Possible errno values

EBADF - The mqdes argument is not a valid message queue descriptor open for reading.
EMSGSIZE - The specified message buffer size, msg_len, is less than the message size attribute of the message queue.
ETIMEDOUT - The O_NONBLOCK flag was not set when the message queue was opened, but no message arrived on the queue before the specified timeout expired.
EAGAIN - O_NONBLOCK was set in the message description associated with mqdes, and the specified message queue is empty.

◆ mq_send()

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

Send a message to a message queue.

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

Note
msg_prio argument is not supported.
Return values
0- Upon successful completion.
-1- An error occurred. errno is also set.
Side Effects Possible errno values

EBADF - The mqdes argument is not a valid message queue descriptor open for writing.
EMSGSIZE - The specified message length, msg_len, exceeds the message size attribute of the message queue, OR insufficient memory for the message to be sent.
ETIMEDOUT - The O_NONBLOCK flag was not set when the message queue was opened, but the timeout expired before the message could be added to the queue.
EAGAIN - The O_NONBLOCK flag is set in the message queue description associated with mqdes, and the specified message queue is full.

◆ mq_timedreceive()

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

Receive a message from a message queue with timeout.

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

Note
msg_prio argument is not supported. Messages are not checked for corruption.
Return values
Thelength of the selected message in bytes - Upon successful completion. The message is removed from the queue
-1- An error occurred. errno is also set.
Side Effects Possible errno values

EBADF - The mqdes argument is not a valid message queue descriptor open for reading.
EMSGSIZE - The specified message buffer size, msg_len, is less than the message size attribute of the message queue.
EINVAL - The process or thread would have blocked, and the abstime parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.
ETIMEDOUT - The O_NONBLOCK flag was not set when the message queue was opened, but no message arrived on the queue before the specified timeout expired.
EAGAIN - O_NONBLOCK was set in the message description associated with mqdes, and the specified message queue is empty.

◆ mq_timedsend()

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

Send a message to a message queue with timeout.

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

Note
msg_prio argument is not supported.
Return values
0- Upon successful completion.
-1- An error occurred. errno is also set.
Side Effects Possible errno values

EBADF - The mqdes argument is not a valid message queue descriptor open for writing.
EMSGSIZE - The specified message length, msg_len, exceeds the message size attribute of the message queue, OR insufficient memory for the message to be sent.
EINVAL - The process or thread would have blocked, and the abstime parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.
ETIMEDOUT - The O_NONBLOCK flag was not set when the message queue was opened, but the timeout expired before the message could be added to the queue.
EAGAIN - The O_NONBLOCK flag is set in the message queue description associated with mqdes, and the specified message queue is full.

◆ mq_unlink()

int mq_unlink ( const char *  name)

Remove a message queue.

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

Return values
0- Upon successful completion.
-1- An error occurred. errno is also set.
Side Effects Possible errno values

EINVAL - name argument is invalid. Refer to requirements on name argument in mq_open().
ENOENT - The named message queue does not exist.