rom/exec/waitport.c

   1 /*
   2     Copyright © 1995-2017, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Wait for a message on a port.
   6     Lang: english
   7 */
   8
   9 #define DEBUG 0
  10 #include <aros/debug.h>
  11
  12 #include "exec_intern.h"
  13 #include <exec/ports.h>
  14 #include <aros/libcall.h>
  15 #include <proto/exec.h>
  16
  17 /*****************************************************************************
  18
  19     NAME */
  20
  21         AROS_LH1(struct Message *, WaitPort,
  22
  23 /*  SYNOPSIS */
  24         AROS_LHA(struct MsgPort *, port, A0),
  25
  26 /*  LOCATION */
  27         struct ExecBase *, SysBase, 64, Exec)
  28
  29 /*  FUNCTION
  30         Wait until a message arrives at the given port. If there is already
  31         a message in it this function returns immediately.
  32
  33     INPUTS
  34         port    - Pointer to messageport.
  35
  36     RESULT
  37         Pointer to the first message that arrived at the port. The message
  38         is _not_ removed from the port. GetMsg() does this for you.
  39
  40     NOTES
  41
  42     EXAMPLE
  43
  44     BUGS
  45
  46     SEE ALSO
  47         WaitPort(), GetMsg()
  48
  49     INTERNALS
  50
  51 ******************************************************************************/
  52 {
  53     AROS_LIBFUNC_INIT
  54
  55     ASSERT_VALID_PTR(port);
  56     /*
  57         On uniprocessors systems, Disable() is not necessary  since emptiness
  58             can be checked without it - and nobody is allowed to change the signal bit as soon
  59         as the current task entered WaitPort() (and probably did not yet
  60         have a chance to Disable()).
  61     */
  62     D(bug("[Exec] WaitPort(0x%p)\n", port);)
  63
  64     /* Is messageport empty? */
  65 #if defined(__AROSEXEC_SMP__)
  66     Disable();
  67     EXEC_SPINLOCK_LOCK(&port->mp_SpinLock, NULL, SPINLOCK_MODE_READ);
  68 #endif
  69     while (IsListEmpty(&port->mp_MsgList))
  70     {
  71 #if defined(__AROSEXEC_SMP__)
  72         EXEC_SPINLOCK_UNLOCK(&port->mp_SpinLock);
  73         Enable();
  74 #endif
  75         D(bug("[Exec] WaitPort: Msg list empty, waiting for activity...\n");)
  76
  77         /*
  78             Yes. Wait for the signal to arrive. Remember that signals may
  79             arrive without a message so check again.
  80         */
  81         Wait(1<<port->mp_SigBit);
  82
  83         D(bug("[Exec] WaitPort: Msgport signal received ...\n");)
  84 #if defined(__AROSEXEC_SMP__)
  85         Disable();
  86         EXEC_SPINLOCK_LOCK(&port->mp_SpinLock, NULL, SPINLOCK_MODE_READ);
  87 #endif
  88     }
  89 #if defined(__AROSEXEC_SMP__)
  90     EXEC_SPINLOCK_UNLOCK(&port->mp_SpinLock);
  91     Enable();
  92 #endif
  93
  94     D(bug("[Exec] WaitPort: Returning...\n");)
  95
  96     /* Return the first node in the list. */
  97     return (struct Message *)port->mp_MsgList.lh_Head;
  98
  99     AROS_LIBFUNC_EXIT
 100 } /* WaitPort() */
 101