gcc/ada/s-tassta.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
   4 --                                                                          --
   5 --                 S Y S T E M . T A S K I N G . S T A G E S                --
   6 --                                                                          --
   7 --                                  S p e c                                 --
   8 --                                                                          --
   9 --                                                                          --
  10 --          Copyright (C) 1992-1999, Free Software Foundation, Inc.         --
  11 --                                                                          --
  12 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNARL was developed by the GNARL team at Florida State University. It is --
  31 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  32 -- State University (http://www.gnat.com).                                  --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 --  This package represents the high level tasking interface used by the
  37 --  compiler to expand Ada 95 tasking constructs into simpler run time calls
  38 --  (aka GNARLI, GNU Ada Run-time Library Interface)
  39
  40 --  Note: Only the compiler is allowed to use this interface, by generating
  41 --  direct calls to it, via Rtsfind.
  42 --  Any changes to this interface may require corresponding compiler changes
  43 --  in exp_ch9.adb and possibly exp_ch7.adb
  44
  45 with System.Task_Info;
  46 --  used for Task_Info_Type
  47
  48 with System.Parameters;
  49 --  used for Size_Type
  50
  51 package System.Tasking.Stages is
  52    pragma Elaborate_Body;
  53
  54    --   The compiler will expand in the GNAT tree the following construct:
  55    --
  56    --   task type T (Discr : Integer);
  57    --
  58    --   task body T is
  59    --      ...declarations, possibly some controlled...
  60    --   begin
  61    --      ...B...;
  62    --   end T;
  63    --
  64    --   T1 : T (1);
  65    --
  66    --  as follows:
  67    --
  68    --   enter_master.all;
  69    --
  70    --   _chain : aliased activation_chain;
  71    --   _init_proc (_chain);
  72    --
  73    --   task type t (discr : integer);
  74    --   tE : aliased boolean := false;
  75    --   tZ : size_type := unspecified_size;
  76    --   type tV (discr : integer) is limited record
  77    --      _task_id : task_id;
  78    --   end record;
  79    --   procedure tB (_task : access tV);
  80    --   freeze tV [
  81    --      procedure _init_proc (_init : in out tV; _master : master_id;
  82    --        _chain : in out activation_chain; _task_id : in task_image_type;
  83    --        discr : integer) is
  84    --      begin
  85    --         _init.discr := discr;
  86    --         _init._task_id := null;
  87    --         create_task (unspecified_priority, tZ,
  88    --           unspecified_task_info, 0, _master,
  89    --           task_procedure_access!(tB'address),
  90    --           _init'address, tE'unchecked_access, _chain, _task_id, _init.
  91    --           _task_id);
  92    --         return;
  93    --      end _init_proc;
  94    --   ]
  95    --
  96    --   procedure tB (_task : access tV) is
  97    --      discr : integer renames _task.discr;
  98    --
  99    --      procedure _clean is
 100    --      begin
 101    --         abort_defer.all;
 102    --         complete_task;
 103    --         finalize_list (F14b);
 104    --         abort_undefer.all;
 105    --         return;
 106    --      end _clean;
 107    --   begin
 108    --      abort_undefer.all;
 109    --      ...declarations...
 110    --      complete_activation;
 111    --      ...B...;
 112    --      return;
 113    --   at end
 114    --      _clean;
 115    --   end tB;
 116    --
 117    --   tE := true;
 118    --   t1 : t (1);
 119    --   master : constant master_id := current_master.all;
 120    --   t1I : task_image_type := new string'"t1";
 121    --   _init_proc (t1, _master, _chain, t1I, 1);
 122    --
 123    --   activate_tasks (_chain'unchecked_access);
 124
 125    procedure Abort_Tasks (Tasks : Task_List);
 126    --  Compiler interface only. Do not call from within the RTS.
 127    --  Initiate abortion, however, the actual abortion is done by abortee by
 128    --  means of Abort_Handler and Abort_Undefer
 129    --
 130    --  source code:
 131    --     Abort T1, T2;
 132    --  code expansion:
 133    --     abort_tasks (task_list'(t1._task_id, t2._task_id));
 134
 135    procedure Activate_Tasks (Chain_Access : Activation_Chain_Access);
 136    --  Compiler interface only. Do not call from within the RTS.
 137    --  This must be called by the creator of a chain of one or more new tasks,
 138    --  to activate them. The chain is a linked list that up to this point is
 139    --  only known to the task that created them, though the individual tasks
 140    --  are already in the All_Tasks_List.
 141    --
 142    --  The compiler builds the chain in LIFO order (as a stack). Another
 143    --  version of this procedure had code to reverse the chain, so as to
 144    --  activate the tasks in the order of declaration. This might be nice, but
 145    --  it is not needed if priority-based scheduling is supported, since all
 146    --  the activated tasks synchronize on the activators lock before they
 147    --  start activating and so they should start activating in priority order.
 148
 149    procedure Complete_Activation;
 150    --  Compiler interface only. Do not call from within the RTS.
 151    --  This should be called from the task body at the end of
 152    --  the elaboration code for its declarative part.
 153    --  Decrement the count of tasks to be activated by the activator and
 154    --  wake it up so it can check to see if all tasks have been activated.
 155    --  Except for the environment task, which should never call this procedure,
 156    --  T.Activator should only be null iff T has completed activation.
 157
 158    procedure Complete_Master;
 159    --  Compiler interface only.  Do not call from within the RTS. This must
 160    --  be called on exit from any master where Enter_Master was called.
 161    --  Assume abort is deferred at this point.
 162
 163    procedure Complete_Task;
 164    --  Compiler interface only. Do not call from within the RTS.
 165    --  This should be called from an implicit at-end handler
 166    --  associated with the task body, when it completes.
 167    --  From this point, the current task will become not callable.
 168    --  If the current task have not completed activation, this should be done
 169    --  now in order to wake up the activator (the environment task).
 170
 171    procedure Create_Task
 172      (Priority      : Integer;
 173       Size          : System.Parameters.Size_Type;
 174       Task_Info     : System.Task_Info.Task_Info_Type;
 175       Num_Entries   : Task_Entry_Index;
 176       Master        : Master_Level;
 177       State         : Task_Procedure_Access;
 178       Discriminants : System.Address;
 179       Elaborated    : Access_Boolean;
 180       Chain         : in out Activation_Chain;
 181       Task_Image    : System.Task_Info.Task_Image_Type;
 182       Created_Task  : out Task_ID);
 183    --  Compiler interface only. Do not call from within the RTS.
 184    --  This must be called to create a new task.
 185    --
 186    --  Priority is the task's priority (assumed to be in the
 187    --   System.Any_Priority'Range)
 188    --  Size is the stack size of the task to create
 189    --  Task_Info is the task info associated with the created task, or
 190    --   Unspecified_Task_Info if none.
 191    --  State is the compiler generated task's procedure body
 192    --  Discriminants is a pointer to a limited record whose discriminants
 193    --   are those of the task to create. This parameter should be passed as
 194    --   the single argument to State.
 195    --  Elaborated is a pointer to a Boolean that must be set to true on exit
 196    --   if the task could be successfully elaborated.
 197    --  Chain is a linked list of task that needs to be created. On exit,
 198    --   Created_Task.Activation_Link will be Chain.T_ID, and Chain.T_ID
 199    --   will be Created_Task (e.g the created task will be linked at the front
 200    --   of Chain).
 201    --  Task_Image is a pointer to a string created by the compiler that the
 202    --   run time can store to ease the debugging and the
 203    --   Ada.Task_Identification facility.
 204    --  Created_Task is the resulting task.
 205    --
 206    --  This procedure can raise Storage_Error if the task creation failed.
 207
 208    function Current_Master return Master_Level;
 209    --  Compiler interface only.
 210    --  This is called to obtain the current master nesting level.
 211
 212    procedure Enter_Master;
 213    --  Compiler interface only.  Do not call from within the RTS.
 214    --  This must be called on entry to any "master" where a task,
 215    --  or access type designating objects containing tasks, may be
 216    --  declared.
 217
 218    procedure Expunge_Unactivated_Tasks (Chain : in out Activation_Chain);
 219    --  Compiler interface only.  Do not call from within the RTS.
 220    --  This must be called by the compiler-generated code for an allocator if
 221    --  the allocated object contains tasks, if the allocator exits without
 222    --  calling Activate_Tasks for a given activation chains, as can happen if
 223    --  an exception occurs during initialization of the object.
 224    --
 225    --  This should be called ONLY for tasks created via an allocator. Recovery
 226    --  of storage for unactivated local task declarations is done by
 227    --  Complete_Master and Complete_Task.
 228    --
 229    --  We remove each task from Chain and All_Tasks_List before we free the
 230    --  storage of its ATCB.
 231    --
 232    --  In other places where we recover the storage of unactivated tasks, we
 233    --  need to clean out the entry queues, but here that should not be
 234    --  necessary, since these tasks should not have been visible to any other
 235    --  tasks, and so no task should be able to queue a call on their entries.
 236    --
 237    --  Just in case somebody misuses this subprogram, there is a check to
 238    --  verify this condition.
 239
 240    procedure Finalize_Global_Tasks;
 241    --  This should be called to complete the execution of the environment task
 242    --  and shut down the tasking runtime system. It is the equivalent of
 243    --  Complete_Task, but for the environment task.
 244    --
 245    --  The environment task must first call Complete_Master, to wait for user
 246    --  tasks that depend on library-level packages to terminate. It then calls
 247    --  Abort_Dependents to abort the "independent" library-level server tasks
 248    --  that are created implicitly by the RTS packages (signal and timer server
 249    --  tasks), and then waits for them to terminate. Then, it calls
 250    --  Vulnerable_Complete_Task.
 251    --
 252    --  It currently also executes the global finalization list, and then resets
 253    --  the "soft links".
 254
 255    procedure Free_Task (T : Task_ID);
 256    --  Recover all runtime system storage associated with the task T, but only
 257    --  if T has terminated. Do nothing in the other case. It is called from
 258    --  Unchecked_Deallocation, for objects that are or contain tasks.
 259
 260    function Terminated (T : Task_ID) return Boolean;
 261    --  This is called by the compiler to implement the 'Terminated attribute.
 262    --  Though is not required to be so by the ARM, we choose to synchronize
 263    --  with the task's ATCB, so that this is more useful for polling the state
 264    --  of a task, and so that it becomes an abort completion point for the
 265    --  calling task (via Undefer_Abort).
 266    --
 267    --  source code:
 268    --     T1'Terminated
 269    --
 270    --  code expansion:
 271    --     terminated (t1._task_id)
 272
 273 end System.Tasking.Stages;