mq_clocksend()
Send a message to a message queue with a timeout measured against a specific clock
Synopsis:
#include <mqueue.h>
#include <time.h>
int mq_clocksend(
mqd_t mqdes,
const char *msg_ptr,
size_t msg_len,
unsigned msg_prio,
clockid_t clk,
const struct timespec *abs_timeout );
Arguments:
- mqdes
- The descriptor of the message queue you want to put the message into, returned by mq_open().
- msg_ptr
- A pointer to the message data.
- msg_len
- The size of the buffer, in bytes.
- msg_prio
- The priority of the message, in the range from 0 through (MQ_PRIO_MAX - 1).
- clk
- The clock against which the time limit is measured. The clock source is specified using the clk variable. The clk variable must be set to either CLOCK_REALTIME, CLOCK_ SOFTTIME or CLOCK_MONOTONIC.
- abs_timeout
- A pointer to a timespec structure that specifies the absolute time (not the relative time to the current time) to wait before the function stops trying to send messages.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The mq_clocksend() function puts a message of size msg_len and pointed to by msg_ptr into the queue indicated by mqdes. The new message has a priority of msg_prio.
The queue maintained is in priority order, and in FIFO order within the same priority.
If the number of elements on the specified queue is equal to its mq_maxmsg, and O_NONBLOCK wasn't set (in the oflag argument to mq_open()), the call to mq_clocksend() blocks. It becomes unblocked when there's room on the queue to send the given message. If more than one mq_clocksend() is blocked on a given queue, and space becomes available in that queue to send, then the mq_clocksend() with the highest priority message is unblocked.
Returns:
-1 if an error occurred (errno is set). Any other value indicates success.
Errors:
- EAGAIN
- The O_NONBLOCK flag was set when opening the queue, and the specified queue is full.
- EBADF
- The mqdes argument doesn't represent a valid message queue descriptor, or mqdes isn't opened for writing.
- EINTR
- The call was interrupted by a signal.
- EINVAL
- One of the following is true:
- The clock is used in a context which does not make sense for a timeout; for example, when using CLOCK_THREAD_CPUTIME_ID.
- The use of the clock as a timeout is not supported; for example, when using another thread's CPUTIME clock.
- The clock does not exist.
- The value of msg_prio is greater than (MQ_PRIO_MAX - 1).
- The process or thread would have blocked, and the abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.
- EMSGSIZE
- The msg_len argument is greater than the msgsize associated with the specified queue.
- ETIMEDOUT
- The timeout value was exceeded.
Classification:
| Safety: | |
|---|---|
| Cancellation point | Yes |
| Signal handler | Yes |
| Thread | Yes |