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MQ_RECEIVE(3)		   Linux Programmer's Manual		 MQ_RECEIVE(3)

       mq_receive, mq_timedreceive - receive a message from a message queue

       #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)):

	   _POSIX_C_SOURCE >= 200112L

       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 argu-
       ment 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 mes-

       If the queue is empty, then, by default, mq_receive()  blocks  until  a
       message	becomes available, or the call is interrupted by a signal han-
       dler.  If the O_NONBLOCK flag is enabled for the message queue descrip-
       tion, 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 speci-
       fies 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.

       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.

       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

       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.

	      msg_len  was  less  than the mq_msgsize attribute of the message

	      The call timed out before a message could be transferred.

       For  an	explanation  of	 the  terms  used   in	 this	section,   see

       |Interface			| Attribute	| Value	  |
       |mq_receive(), mq_timedreceive() | Thread safety | MT-Safe |
       POSIX.1-2001, POSIX.1-2008.

       On  Linux,  mq_timedreceive()  is  a system call, and mq_receive() is a
       library function layered on top of that system call.

       mq_close(3),  mq_getattr(3),  mq_notify(3),   mq_open(3),   mq_send(3),
       mq_unlink(3), mq_overview(7), time(7)

       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at

Linux				  2016-12-12			 MQ_RECEIVE(3)