mqueue接口介绍
需要包含头文件#include <posix/mqueue.h>;
定义了系统消息队列相关的接口
Header File
Functions
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int mq_close(mqd_t mqdes)
Close a message queue.
http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_close.html
@sideeffect Possible errno values
EBADF - The mqdes argument is not a valid message queue descriptor.
- Return values
0 – - Upon successful completion
-1 – - A error occurred. errno is also set.
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int mq_getattr(mqd_t mqdes, struct mq_attr *mqstat)
Get message queue attributes.
http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_getattr.html
@sideeffect Possible errno values
DBADF - The mqdes argument is not a valid message queue descriptor.
- Return values
0 – - Upon successful completion
-1 – - A error occurred. errno is also set.
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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
@sideeffect 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.备注
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.
备注
mode argument is not supported.
备注
Supported oflags: O_RDWR, O_CREAT, O_EXCL, and O_NONBLOCK.
- Return values
Message – queue descriptor — Upon successful completion
(mqd_t) – - 1 — An error occurred. errno is also set.
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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
@sideeffect 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.备注
msg_prio argument is not supported. Messages are not checked for corruption.
- Return values
The – length of the selected message in bytes - Upon successful completion. The message is removed from the queue
-1 – - An error occurred. errno is also set.
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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
@sideeffect 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.备注
msg_prio argument is not supported.
- Return values
0 – - Upon successful completion.
-1 – - An error occurred. errno is also set.
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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
@sideeffect 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.
备注
msg_prio argument is not supported. Messages are not checked for corruption.
- Return values
The – length of the selected message in bytes - Upon successful completion. The message is removed from the queue
-1 – - An error occurred. errno is also set.
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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
@sideeffect 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.
备注
msg_prio argument is not supported.
- Return values
0 – - Upon successful completion.
-1 – - An error occurred. errno is also set.
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int mq_unlink(const char *name)
Remove a message queue.
http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_unlink.html
@sideeffect 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.
- Return values
0 – - Upon successful completion.
-1 – - An error occurred. errno is also set.
Structures
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struct mq_attr
Message queue attributes.
Type Definitions
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typedef void *mqd_t
Message queue descriptor.