rom/exec/permit.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Permit() - Allow tasks switches to occur.
   6     Lang: english
   7 */
   8
   9 #include <exec/types.h>
  10 #include <exec/execbase.h>
  11 #include <aros/libcall.h>
  12 #include <aros/atomic.h>
  13 #include <proto/exec.h>
  14
  15 /*****************************************************************************/
  16 #undef  Exec
  17 #ifdef UseExecstubs
  18 #    define Exec _Exec
  19 #endif
  20
  21 /*  NAME */
  22
  23         AROS_LH0(void, Permit,
  24
  25 /*  LOCATION */
  26         struct ExecBase *, SysBase, 23, Exec)
  27
  28 /*  FUNCTION
  29         This function will reactivate the task dispatcher after a call
  30         to Forbid(). Note that calls to Forbid() nest, and for every
  31         call to Forbid() you need a matching call to Permit().
  32
  33     INPUTS
  34         None.
  35
  36     RESULT
  37         Multitasking will be re-enabled.
  38
  39     NOTES
  40         This function preserves all registers.
  41
  42         To prevent deadlocks calling Wait() in forbidden state breaks
  43         the forbid - thus taskswitches may happen again.
  44
  45     EXAMPLE
  46         No you really don't want to use this function.
  47
  48     BUGS
  49         The only architecture that you can rely on the registers being
  50         saved is on the Motorola mc68000 family.
  51
  52     SEE ALSO
  53         Forbid(), Disable(), Enable(), Wait()
  54
  55     INTERNALS
  56         If you want to preserve all the registers, replace this function
  57         in your $(KERNEL) directory. Otherwise this function is
  58         satisfactory.
  59
  60 ******************************************************************************/
  61 {
  62 #undef Exec
  63
  64     AROS_LIBFUNC_INIT
  65
  66     /*
  67         Task switches are allowed again, if a switch is pending, we
  68         should allow it.
  69     */
  70 #if 1
  71     AROS_ATOMIC_DEC(SysBase->TDNestCnt);
  72 #else
  73     AROS_ATOMIC_DEC(SysBase->TDNestCnt);
  74
  75     if(    ( SysBase->TDNestCnt < 0 )
  76         && ( SysBase->IDNestCnt < 0 )
  77         && ( SysBase->AttnResched & 0x80 ) )
  78     {
  79         /* Haha, you re-enabled multitasking, only to have the rug
  80            pulled out from under you feet :)
  81
  82             Clear the Switch() pending flag.
  83         */
  84
  85         Disable();
  86         SysBase->AttnResched &= ~0x80;
  87         Switch();
  88         Enable();
  89     }
  90 #endif
  91
  92     AROS_LIBFUNC_EXIT
  93 } /* Permit() */