получить сообщение из очереди сообщений (receive a message from a message queue)
Имя (Name)
mq_receive, mq_timedreceive - receive a message from a message
queue
Синопсис (Synopsis)
#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 *restrict msg_ptr,
size_t msg_len, unsigned int *restrict msg_prio,
const struct timespec *restrict abs_timeout);
Link with -lrt.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
mq_timedreceive():
_POSIX_C_SOURCE >= 200112L
Описание (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.
Возвращаемое значение (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.
Ошибки (Error)
EAGAIN The queue was empty, and the O_NONBLOCK flag was set for
the message queue description referred to by mqdes.
EBADF The descriptor specified in mqdes was invalid or not
opened for reading.
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.
Атрибуты (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 │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
On Linux, mq_timedreceive() is a system call, and mq_receive() is
a library function layered on top of that system call.
Смотри также (See also)
mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_send(3),
mq_unlink(3), mq_overview(7), time(7)
