Other Alias
mq_receiveSYNOPSIS
#include <mqueue.h>
ssize_t mq_receive(mqd_t mqdes, char *msg_ptr,
size_t msg_len, unsigned int *msg_prio);
#include <time.h>
#include <mqueue.h>
ssize_t mq_timedreceive(mqd_t mqdes, char *msg_ptr,
size_t msg_len, unsigned int *msg_prio,
const struct timespec *abs_timeout);
Link with -lrt.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
mq_timedreceive():
- _POSIX_C_SOURCE >= 200112L
DESCRIPTION
mq_receive() removes the oldest message with the highest priority from the message queue referred to by the message queue descriptor mqdes, and places it in the buffer pointed to by msg_ptr. The msg_len argument specifies the size of the buffer pointed to by msg_ptr; this must be greater than or equal to the mq_msgsize attribute of the queue (see mq_getattr(3)). If msg_prio is not NULL, then the buffer to which it points is used to return the priority associated with the received message.If the queue is empty, then, by default, mq_receive() blocks until a message becomes available, or the call is interrupted by a signal handler. If the O_NONBLOCK flag is enabled for the message queue description, then the call instead fails immediately with the error EAGAIN.
mq_timedreceive() behaves just like mq_receive(), except that if the queue is empty and the O_NONBLOCK flag is not enabled for the message queue description, then abs_timeout points to a structure which specifies how long the call will block. This value is an absolute timeout in seconds and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), specified in the following structure:
struct timespec { time_t tv_sec; /* seconds */ long tv_nsec; /* nanoseconds */ };If no message is available, and the timeout has already expired by the time of the call, mq_timedreceive() returns immediately.
RETURN VALUE
On success, mq_receive() and mq_timedreceive() return the number of bytes in the received message; on error, -1 is returned, with errno set to indicate the error.ERRORS
- EAGAIN
- The queue was empty, and the O_NONBLOCK flag was set for the message queue description referred to by mqdes.
- EBADF
- The file descriptor specified in mqdes was invalid.
- EINTR
- The call was interrupted by a signal handler; see signal(7).
- EINVAL
- The call would have blocked, and abs_timeout was invalid, either because tv_sec was less than zero, or because tv_nsec was less than zero or greater than 1000 million.
- EMSGSIZE
- msg_len was less than the mq_msgsize attribute of the message queue.
- ETIMEDOUT
- The call timed out before a message could be transferred.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface | Attribute | Value |
mq_receive(), mq_timedreceive() | Thread safety | MT-Safe |
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.NOTES
On Linux, mq_timedreceive() is a system call, and mq_receive() is a library function layered on top of that system call.COLOPHON
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