rom/exec/reschedule.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Reschedule() - Put a task back into the ready or waiting list.
   6     Lang: english
   7 */
   8
   9 #include <aros/debug.h>
  10 #include <exec/types.h>
  11 #include <exec/execbase.h>
  12 #include <aros/libcall.h>
  13
  14 /*****i***********************************************************************
  15
  16     NAME */
  17 #include <proto/exec.h>
  18
  19         AROS_LH1(void, Reschedule,
  20
  21 /*  SYNOPSIS */
  22         AROS_LHA(struct Task *, task, A0),
  23
  24 /*  LOCATION */
  25         struct ExecBase *, SysBase, 8, Exec)
  26
  27 /*  FUNCTION
  28         Reschedule will place the task into one of Execs internal task
  29         lists. Which list it is placed in will depend upon whether the
  30         task is ready to run, or whether it is waiting for an external
  31         event to awaken it.
  32
  33         It is possible that in the future, more efficient schedulers
  34         will be implemented. In which case this is the function that they
  35         need to implement.
  36
  37         You should not do any costly calculations since you will be
  38         running in interupt mode.
  39
  40     INPUTS
  41         task    -   The task to insert into the list.
  42
  43     RESULT
  44         The task will be inserted into one of Exec's task lists.
  45
  46     NOTES
  47         Not actually complete yet. Some of the task states don't have any
  48         supplied action.
  49
  50     EXAMPLE
  51
  52     BUGS
  53         Only in relation to the comments within about low-priority tasks
  54         not getting any processor time.
  55
  56     SEE ALSO
  57
  58     INTERNALS
  59
  60 ******************************************************************************/
  61 {
  62     AROS_LIBFUNC_INIT
  63
  64     /*
  65         The code in here defines how "good" the task switching is.
  66         There are seveal things which should be taken into account:
  67
  68         1. No task should block the CPU forever even if it is an
  69             endless loop.
  70
  71         2. Tasks with a higher priority should get the CPU more often.
  72
  73         3. Tasks with a low priority should get the CPU every now and then.
  74
  75         Enqueue() fulfills 2 but not 1 and 3. AddTail() fulfills 1 and 3.
  76
  77         A better way would be to "deteriorate" a task, ie. decrease the
  78         priority and use Enqueue() but at this time, I can't do this
  79         because I have no good way to extend the task structure (I
  80         need a variable to store the original prio).
  81     */
  82
  83    /* Somebody had better have set the tasks state properly */
  84
  85     switch(task->tc_State)
  86     {
  87         case TS_READY:
  88             Enqueue(&SysBase->TaskReady, (struct Node *)task);
  89             break;
  90
  91         case TS_ADDED:
  92             Enqueue(&SysBase->TaskReady, (struct Node *)task);
  93             break;
  94
  95         /*
  96             We don't need to Enqueue() onto the TaskWait list,
  97             as it is not sorted - saves quite a few cycles in
  98             the long run.
  99         */
 100         case TS_WAIT:
 101             AddTail(&SysBase->TaskWait, (struct Node *)task);
 102             break;
 103
 104         case TS_REMOVED:
 105             /* Ideally we should free the task here, but we can't
 106                because that would corrupt the memory lists.
 107             */
 108             break;
 109
 110         case TS_INVALID:
 111         case TS_EXCEPT:
 112         case TS_RUN:
 113             /* We should never be called with this state. */
 114             ASSERT(FALSE);
 115             break;
 116     }
 117
 118     AROS_LIBFUNC_EXIT
 119 } /* Reschedule */