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mq_receive (2)
  • >> mq_receive (2) ( FreeBSD man: Системные вызовы )
  • mq_receive (3) ( Solaris man: Библиотечные вызовы )
  • mq_receive (3) ( Linux man: Библиотечные вызовы )
  • mq_receive (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    mq_receive , mq_timedreceive
    
     - receive a message from message queue (REALTIME)
    
     
    

    LIBRARY

    Lb librt
    
     
    

    SYNOPSIS

       #include <mqueue.h>
    ssize_t Fo mq_receive Fa mqd_t mqdes Fa char *msg_ptr Fa size_t msg_len Fa unsigned *msg_prio Fc Ft ssize_t Fo mq_timedreceive Fa mqd_t mqdes Fa char *msg_ptr Fa size_t msg_len Fa unsigned *msg_prio Fa const struct timespec *abs_timeout Fc  

    DESCRIPTION

    The mq_receive ();
    system call receives oldest of the highest priority message(s) from the message queue specified by Fa mqdes . If the size of the buffer in bytes, specified by the Fa msg_len argument, is less than the mq_msgsize attribute of the message queue, the system call will fail and return an error. Otherwise, the selected message will be removed from the queue and copied to the buffer pointed to by the Fa msg_ptr argument.

    If the argument Fa msg_prio is not NULL the priority of the selected message will be stored in the location referenced by Fa msg_prio . If the specified message queue is empty and O_NONBLOCK is not set in the message queue description associated with Fa mqdes , mq_receive ();
    will block until a message is enqueued on the message queue or until mq_receive ();
    is interrupted by a signal. If more than one thread is waiting to receive a message when a message arrives at an empty queue and the Priority Scheduling option is supported, then the thread of highest priority that has been waiting the longest will be selected to receive the message. Otherwise, it is unspecified which waiting thread receives the message. If the specified message queue is empty and O_NONBLOCK is set in the message queue description associated with Fa mqdes , no message will be removed from the queue, and mq_receive ();
    will return an error.

    The mq_timedreceive ();
    system call will receive the oldest of the highest priority messages from the message queue specified by Fa mqdes as described for the mq_receive ();
    system call. However, if O_NONBLOCK was not specified when the message queue was opened via the mq_open ();
    system call, and no message exists on the queue to satisfy the receive, the wait for such a message will be terminated when the specified timeout expires. If O_NONBLOCK is set, this system call is equivalent to mq_receive (.);

    The timeout expires when the absolute time specified by Fa abs_timeout passes, as measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds Fa abs_timeout ) , or if the absolute time specified by Fa abs_timeout has already been passed at the time of the call.

    The timeout is based on the CLOCK_REALTIME clock.  

    RETURN VALUES

    Upon successful completion, the mq_receive ();
    and mq_timedreceive ();
    system calls return the length of the selected message in bytes and the message is removed from the queue. Otherwise, no message is removed from the queue, the system call returns a value of -1, and the global variable errno is set to indicate the error.  

    ERRORS

    The mq_receive ();
    and mq_timedreceive ();
    system calls will fail if:

    Bq Er EAGAIN
    O_NONBLOCK flag is set in the message queue description associated with Fa mqdes , and the specified message queue is empty.
    Bq Er EBADF
    The Fa mqdes argument is not a valid message queue descriptor open for reading.
    Bq Er EMSGSIZE
    The specified message buffer size, Fa msg_len , is less than the message size attribute of the message queue.
    Bq Er EINTR
    The mq_receive ();
    or mq_timedreceive ();
    operation was interrupted by a signal.
    Bq Er EINVAL
    The process or thread would have blocked, and the Fa abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.
    Bq Er ETIMEDOUT
    The O_NONBLOCK flag was not set when the message queue was opened, but no message arrived on the queue before the specified timeout expired.

     

    SEE ALSO

    mq_open2, mq_send2, mq_timedsend2  

    STANDARDS

    The mq_receive ();
    and mq_timedreceive ();
    system calls conform to St -p1003.1-2004 .  

    HISTORY

    Support for POSIX message queues first appeared in Fx 7.0 .  

    COPYRIGHT

    Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at         http://www.opengroup.org/unix/online.html.


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    SEE ALSO
    STANDARDS
    HISTORY
    COPYRIGHT


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