mq_clockreceive()
Receive a message from a message queue with a timeout measured against a specific clock
Synopsis:
#include <mqueue.h>
#include <time.h>
ssize_t mq_clockreceive(
mqd_t mqdes,
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 receive a message from, returned by mq_open().
- msg_ptr
- A pointer to a buffer where the function can store the message data.
- msg_len
- The size of the buffer, in bytes.
- msg_prio
- NULL, or a pointer to a location where the function can store the priority of the message that it removed from the queue.
- 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 receive messages.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The mq_clockreceive() function receives the oldest of the highest priority messages in the queue specified by mqdes.
If you call mq_clockreceive() with a msg_len of anything other than the mq_msgsize of the specified queue, then mq_clockreceive() returns an error, and errno is set to EINVAL.
If there are no messages on the queue specified, and O_NONBLOCK wasn't set (in the oflag argument to mq_open()), then the mq_clockreceive() call blocks. If multiple mq_clockreceive() calls are blocked on a single queue, then they're unblocked in FIFO order as messages arrive.
Returns:
The size of the message removed from the queue, or -1 if an error occurred (no message is removed from the queue, and errno is set).
Errors:
- EAGAIN
- The O_NONBLOCK flag was set and there are no messages currently on the specified queue.
- EBADF
- The mqdes argument doesn't represent a valid queue open for reading.
- EINTR
- The operation was interrupted by a signal.
- EINVAL
- One of the following:
- 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 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 given msg_len is shorter than the mq_msgsize for the given queue or the given msg_len is too short for the message that would have been received.
- ETIMEDOUT
- The timeout value was exceeded.
Classification:
| Safety: | |
|---|---|
| Cancellation point | Yes |
| Signal handler | Yes |
| Thread | Yes |