MQ_SEND(3) | Library Functions Manual | MQ_SEND(3) |
mq_send
, mq_timedsend
—
#include <mqueue.h>
int
mq_send
(mqd_t mqdes,
const char *msg_ptr, size_t
msg_len, unsigned msg_prio);
#include
<mqueue.h>
#include <time.h>
int
mq_timedsend
(mqd_t mqdes,
const char *msg_ptr, size_t
msg_len, unsigned msg_prio,
const struct timespec *abs_timeout);
mq_send
() function will add the message pointed to
by the argument msg_ptr to the message queue specified
by mqdes. The msg_len argument
specifies the length of the message, in bytes, pointed to by
msg_ptr. The value of msg_len will
be less than or equal to the mq_msgsize attribute of the
message queue, or mq_send
() will fail.
If the specified message queue is not full,
mq_send
() behaves as if the message is inserted into
the message queue at the position indicated by the
msg_prio argument. A message with a larger numeric
value of msg_prio will be inserted before messages
with lower values of msg_prio. A message will be
inserted after other messages in the queue, if any, with equal
msg_prio. The value of msg_prio
will be less than {MQ_PRIO_MAX
}.
If the specified message queue is full and
O_NONBLOCK
is not set in the message queue
description associated with mqdes,
mq_send
() blocks until space becomes available to
enqueue the message, or until mq_send
() is
interrupted by a signal. If more than one thread is waiting to send when
space becomes available in the message queue, then the thread of the highest
priority that has been waiting the longest will be unblocked to send its
message. If the specified message queue is full and
O_NONBLOCK
is set in the message queue description
associated with mqdes, the message will not be queued
and mq_send
() will return an error.
The mq_timedsend
() function will add a
message to the message queue specified by mqdes in the
manner defined for the mq_send
() function. However,
if the specified message queue is full and
O_NONBLOCK
is not set in the message queue
description associated with mqdes, the wait for
sufficient room in the queue will be terminated when the specified timeout
expires. If O_NONBLOCK
is set in the message queue
description, this function will be equivalent to
mq_send
().
The timeout will expire when the absolute time specified by abs_timeout passes, as measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds abs_timeout), or if the absolute time specified by abs_timeout has already been passed at the time of the call.
The resolution of the timeout is based on the CLOCK_REALTIME
clock. The timespec argument is defined in the
<time.h>
header.
Under no circumstance will the operation fail with a timeout if there is sufficient room in the queue to add the message immediately. The validity of the abs_timeout parameter need not be checked when there is sufficient room in the queue.
mq_send
() and
mq_timedsend
() functions return a value of zero.
Otherwise, no message will be enqueued, the functions will return -1, and the
global variable errno will be set to indicate the error.
mq_send
() and mq_timedsend
()
functions fail if:
EAGAIN
]O_NONBLOCK
flag is set in the message queue
description associated with mqdes, and the specified
message queue is full.EBADF
]EINTR
]mq_send
() or
mq_timedsend
().EINVAL
]EMSGSIZE
]ETIMEDOUT
]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.mq_send
() and mq_timedsend
()
functions first appeared in NetBSD 5.0.
June 7, 2010 | NetBSD 9.2 |