MQ_SEND(3) | Library Functions Manual | MQ_SEND(3) |
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);
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.
June 7, 2010 | NetBSD 6.1 |