rom/exec/forbid.c

   1 /*
   2     Copyright © 1995-2017, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Forbid() - Prevent tasks switches from taking place.
   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
  16 #include "exec_intern.h"
  17
  18 #undef Exec
  19 #ifdef UseExecstubs
  20 #    define Exec _Exec
  21 #endif
  22
  23 /*****************************************************************************/
  24
  25
  26 /*  NAME */
  27 #include <proto/exec.h>
  28
  29         AROS_LH0(void, Forbid,
  30
  31 /*  LOCATION */
  32         struct ExecBase *, SysBase, 22, Exec)
  33
  34 /*  FUNCTION
  35         Forbid any further taskswitches (*) until a matching call to Permit().
  36         Naturally disabling taskswitches means:
  37
  38         THIS CALL IS DANGEROUS
  39
  40         Do not use it without thinking very well about it or better
  41         do not use it at all. Most of the time you can live without
  42         it by using semaphores or similar.
  43
  44         Calls to Forbid() nest, i.e. for each call to Forbid() you
  45         need one call to Permit().
  46
  47     INPUTS
  48         None.
  49
  50     RESULT
  51         The multitasking state will be disabled AFTER this function
  52         returns to the caller.
  53
  54     NOTES
  55         This function preserves all registers.
  56
  57         To prevent deadlocks calling Wait() in forbidden state breaks
  58         the forbid - thus taskswitches may happen again.
  59
  60         (*) On EXECSMP builds, Forbid() only aplies to the processor
  61             it is called from. Data which needs to be protected from
  62             parallel access will also require a spinlock.
  63
  64     EXAMPLE
  65         On uniprocessor builds of AROS, it is generally not necessary/
  66         desirable to use Forbid()/Permit() in most userspace code - however for
  67         EXECSMP builds, you will need to protect spinlocks against
  68         task switches on the local processor..
  69
  70     BUGS
  71         The only architecture that you can rely on the registers being
  72         saved is on the Motorola mc68000 family.
  73
  74     SEE ALSO
  75         Permit(), Disable(), Enable(), Wait()
  76
  77     INTERNALS
  78         If you want to preserve all the registers, replace this function
  79         in your $(KERNEL) directory. Otherwise this function is
  80         satisfactory.
  81
  82 ******************************************************************************/
  83 {
  84 #undef Exec
  85
  86     AROS_LIBFUNC_INIT
  87
  88     D(bug("[Exec] Forbid()\n"));
  89
  90     TDNESTCOUNT_INC;
  91
  92     D(bug("[Exec] Forbid: TDNESTCOUNT = %d\n", TDNESTCOUNT_GET);)
  93
  94     AROS_LIBFUNC_EXIT
  95 } /* Forbid() */