rom/exec/permit.c

   1 /*
   2     Copyright © 1995-2017, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Permit() - Allow tasks switches to occur.
   6     Lang: english
   7 */
   8
   9 #define DEBUG 0
  10
  11 #include <exec/types.h>
  12 #include <exec/execbase.h>
  13 #include <aros/libcall.h>
  14 #include <aros/atomic.h>
  15 #include <aros/debug.h>
  16 #include <proto/exec.h>
  17
  18 #include "exec_intern.h"
  19
  20 #undef Exec
  21 #ifdef UseExecstubs
  22 #    define Exec _Exec
  23 #endif
  24
  25 /*****************************************************************************
  26
  27     NAME */
  28
  29         AROS_LH0(void, Permit,
  30
  31 /*  LOCATION */
  32         struct ExecBase *, SysBase, 23, Exec)
  33
  34 /*  FUNCTION
  35         This function will reactivate the task dispatcher (*) after a call
  36         to Forbid(). Note that calls to Forbid() nest, and for every
  37         call to Forbid() you need a matching call to Permit().
  38
  39     INPUTS
  40         None.
  41
  42     RESULT
  43         Multitasking will be re-enabled.
  44
  45     NOTES
  46         This function preserves all registers.
  47
  48         To prevent deadlocks calling Wait() in forbidden state breaks
  49         the forbid - thus taskswitches may happen again.
  50
  51         (*) On EXECSMP builds, Forbid() only aplies to the processor
  52             it is called from. Data which needs to be protected from
  53             parallel access will also require a spinlock.
  54
  55     EXAMPLE
  56         On uniprocessor builds of AROS, it is generally not necessary/
  57         desirable to use Forbid()/Permit() in most userspace code - however for
  58         EXECSMP builds, you will need to protect spinlocks against
  59         task switches on the local processor..
  60
  61     BUGS
  62         The only architecture that you can rely on the registers being
  63         saved is on the Motorola mc68000 family.
  64
  65     SEE ALSO
  66         Forbid(), Disable(), Enable(), Wait()
  67
  68     INTERNALS
  69         If you want to preserve all the registers, replace this function
  70         in your $(KERNEL) directory. Otherwise this function is
  71         satisfactory.
  72
  73     HISTORY
  74
  75
  76 ******************************************************************************/
  77 #undef Exec
  78 {
  79     AROS_LIBFUNC_INIT
  80
  81     D(bug("[Exec] Permit()\n"));
  82
  83     /*
  84      * Task switches are allowed again, if a switch is pending, we
  85      * should allow it.
  86      */
  87     TDNESTCOUNT_DEC;
  88
  89     D(bug("[Exec] Permit: TDNESTCOUNT = %d\n", TDNESTCOUNT_GET));
  90
  91     if (KernelBase && !KrnIsSuper())
  92     {
  93         if(    ( TDNESTCOUNT_GET < 0 )
  94             && ( IDNESTCOUNT_GET < 0 )
  95             && ( FLAG_SCHEDSWITCH_ISSET ) )
  96         {
  97             /*
  98              * Haha, you re-enabled multitasking, only to have the rug
  99              * pulled out from under you feet :)
 100
 101              * Clear the Switch() pending flag.
 102              */
 103             D(bug("[Exec] Permit: rescheduling\n"));
 104             KrnSchedule();
 105         }
 106     }
 107
 108     AROS_LIBFUNC_EXIT
 109 } /* Permit() */