rom/exec/waitport.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Wait for a message on a port.
   6     Lang: english
   7 */
   8 #include "exec_intern.h"
   9 #include <exec/ports.h>
  10 #include <aros/libcall.h>
  11 #include <proto/exec.h>
  12
  13 /*****************************************************************************
  14
  15     NAME */
  16
  17         AROS_LH1(struct Message *, WaitPort,
  18
  19 /*  SYNOPSIS */
  20         AROS_LHA(struct MsgPort *, port, A0),
  21
  22 /*  LOCATION */
  23         struct ExecBase *, SysBase, 64, Exec)
  24
  25 /*  FUNCTION
  26         Wait until a message arrives at the given port. If there is already
  27         a message in it this function returns immediately.
  28
  29     INPUTS
  30         port    - Pointer to messageport.
  31
  32     RESULT
  33         Pointer to the first message that arrived at the port. The message
  34         is _not_ removed from the port. GetMsg() does this for you.
  35
  36     NOTES
  37
  38     EXAMPLE
  39
  40     BUGS
  41
  42     SEE ALSO
  43         WaitPort(), GetMsg()
  44
  45     INTERNALS
  46
  47 ******************************************************************************/
  48 {
  49     AROS_LIBFUNC_INIT
  50
  51     ASSERT_VALID_PTR(port);
  52     /*
  53         No Disable() necessary here since emptiness can be checked
  54         without and nobody is allowed to change the signal bit as soon
  55         as the current task entered WaitPort() (and probably did not yet
  56         have a chance to Disable()).
  57     */
  58
  59     /* Is messageport empty? */
  60     while (IsListEmpty (&port->mp_MsgList))
  61     {
  62         /*
  63             Yes. Wait for the signal to arrive. Remember that signals may
  64             arrive without a message so check again.
  65         */
  66         Wait(1<<port->mp_SigBit);
  67     }
  68
  69     /* Return the first node in the list. */
  70     return (struct Message *)port->mp_MsgList.lh_Head;
  71
  72     AROS_LIBFUNC_EXIT
  73 } /* WaitPort() */
  74