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 --          Copyright (C) 1992-2003, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, USA.                                                      --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNARL was developed by the GNARL team at Florida State University.       --
  30 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This package represents the high level tasking interface used by the
  35 --  compiler to expand Ada 95 tasking constructs into simpler run time calls
  36 --  (aka GNARLI, GNU Ada Run-time Library Interface)
  37
  38 --  Note: Only the compiler is allowed to use this interface, by generating
  39 --  direct calls to it, via Rtsfind.
  40 --  Any changes to this interface may require corresponding compiler changes
  41 --  in exp_ch9.adb and possibly exp_ch7.adb
  42
  43 with System.Task_Info;
  44 --  used for Task_Info_Type
  45
  46 with System.Parameters;
  47 --  used for Size_Type
  48
  49 package System.Tasking.Stages is
  50    pragma Elaborate_Body;
  51
  52    --   The compiler will expand in the GNAT tree the following construct:
  53
  54    --   task type T (Discr : Integer);
  55
  56    --   task body T is
  57    --      ...declarations, possibly some controlled...
  58    --   begin
  59    --      ...B...;
  60    --   end T;
  61
  62    --   T1 : T (1);
  63
  64    --  as follows:
  65
  66    --   enter_master.all;
  67
  68    --   _chain : aliased activation_chain;
  69    --   activation_chainIP (_chain);
  70
  71    --   task type t (discr : integer);
  72    --   tE : aliased boolean := false;
  73    --   tZ : size_type := unspecified_size;
  74    --   type tV (discr : integer) is limited record
  75    --      _task_id : task_id;
  76    --   end record;
  77    --   procedure tB (_task : access tV);
  78    --   freeze tV [
  79    --      procedure tVIP (_init : in out tV; _master : master_id;
  80    --        _chain : in out activation_chain; _task_id : in task_image_type;
  81    --        discr : integer) is
  82    --      begin
  83    --         _init.discr := discr;
  84    --         _init._task_id := null;
  85    --         create_task (unspecified_priority, tZ,
  86    --           unspecified_task_info, 0, _master,
  87    --           task_procedure_access!(tB'address),
  88    --           _init'address, tE'unchecked_access, _chain, _task_id, _init.
  89    --           _task_id);
  90    --         return;
  91    --      end tVIP;
  92    --   ]
  93
  94    --   procedure tB (_task : access tV) is
  95    --      discr : integer renames _task.discr;
  96
  97    --      procedure _clean is
  98    --      begin
  99    --         abort_defer.all;
 100    --         complete_task;
 101    --         finalize_list (F14b);
 102    --         abort_undefer.all;
 103    --         return;
 104    --      end _clean;
 105    --   begin
 106    --      abort_undefer.all;
 107    --      ...declarations...
 108    --      complete_activation;
 109    --      ...B...;
 110    --      return;
 111    --   at end
 112    --      _clean;
 113    --   end tB;
 114
 115    --   tE := true;
 116    --   t1 : t (1);
 117    --   _master : constant master_id := current_master.all;
 118    --   t1S : task_image_type := new string'"t1";
 119    --   task_image_typeIP (t1, _master, _chain, t1S, 1);
 120
 121    --   activate_tasks (_chain'unchecked_access);
 122
 123    procedure Abort_Tasks (Tasks : Task_List);
 124    --  Compiler interface only. Do not call from within the RTS.
 125    --  Initiate abortion, however, the actual abortion is done by abortee by
 126    --  means of Abort_Handler and Abort_Undefer
 127    --
 128    --  source code:
 129    --     Abort T1, T2;
 130    --  code expansion:
 131    --     abort_tasks (task_list'(t1._task_id, t2._task_id));
 132
 133    procedure Activate_Tasks (Chain_Access : Activation_Chain_Access);
 134    --  Compiler interface only. Do not call from within the RTS.
 135    --  This must be called by the creator of a chain of one or more new tasks,
 136    --  to activate them. The chain is a linked list that up to this point is
 137    --  only known to the task that created them, though the individual tasks
 138    --  are already in the All_Tasks_List.
 139    --
 140    --  The compiler builds the chain in LIFO order (as a stack). Another
 141    --  version of this procedure had code to reverse the chain, so as to
 142    --  activate the tasks in the order of declaration. This might be nice, but
 143    --  it is not needed if priority-based scheduling is supported, since all
 144    --  the activated tasks synchronize on the activators lock before they
 145    --  start activating and so they should start activating in priority order.
 146
 147    procedure Complete_Activation;
 148    --  Compiler interface only. Do not call from within the RTS.
 149    --  This should be called from the task body at the end of
 150    --  the elaboration code for its declarative part.
 151    --  Decrement the count of tasks to be activated by the activator and
 152    --  wake it up so it can check to see if all tasks have been activated.
 153    --  Except for the environment task, which should never call this procedure,
 154    --  T.Activator should only be null iff T has completed activation.
 155
 156    procedure Complete_Master;
 157    --  Compiler interface only.  Do not call from within the RTS. This must
 158    --  be called on exit from any master where Enter_Master was called.
 159    --  Assume abort is deferred at this point.
 160
 161    procedure Complete_Task;
 162    --  Compiler interface only. Do not call from within the RTS.
 163    --  This should be called from an implicit at-end handler
 164    --  associated with the task body, when it completes.
 165    --  From this point, the current task will become not callable.
 166    --  If the current task have not completed activation, this should be done
 167    --  now in order to wake up the activator (the environment task).
 168
 169    procedure Create_Task
 170      (Priority      : Integer;
 171       Size          : System.Parameters.Size_Type;
 172       Task_Info     : System.Task_Info.Task_Info_Type;
 173       Num_Entries   : Task_Entry_Index;
 174       Master        : Master_Level;
 175       State         : Task_Procedure_Access;
 176       Discriminants : System.Address;
 177       Elaborated    : Access_Boolean;
 178       Chain         : in out Activation_Chain;
 179       Task_Image    : String;
 180       Created_Task  : out Task_ID);
 181    --  Compiler interface only. Do not call from within the RTS.
 182    --  This must be called to create a new task.
 183    --
 184    --  Priority is the task's priority (assumed to be in the
 185    --   System.Any_Priority'Range)
 186    --  Size is the stack size of the task to create
 187    --  Task_Info is the task info associated with the created task, or
 188    --   Unspecified_Task_Info if none.
 189    --  State is the compiler generated task's procedure body
 190    --  Discriminants is a pointer to a limited record whose discriminants
 191    --   are those of the task to create. This parameter should be passed as
 192    --   the single argument to State.
 193    --  Elaborated is a pointer to a Boolean that must be set to true on exit
 194    --   if the task could be sucessfully elaborated.
 195    --  Chain is a linked list of task that needs to be created. On exit,
 196    --   Created_Task.Activation_Link will be Chain.T_ID, and Chain.T_ID
 197    --   will be Created_Task (e.g the created task will be linked at the front
 198    --   of Chain).
 199    --  Task_Image is a string created by the compiler that the
 200    --   run time can store to ease the debugging and the
 201    --   Ada.Task_Identification facility.
 202    --  Created_Task is the resulting task.
 203    --
 204    --  This procedure can raise Storage_Error if the task creation failed.
 205
 206    function Current_Master return Master_Level;
 207    --  Compiler interface only.
 208    --  This is called to obtain the current master nesting level.
 209
 210    procedure Enter_Master;
 211    --  Compiler interface only.  Do not call from within the RTS.
 212    --  This must be called on entry to any "master" where a task,
 213    --  or access type designating objects containing tasks, may be
 214    --  declared.
 215
 216    procedure Expunge_Unactivated_Tasks (Chain : in out Activation_Chain);
 217    --  Compiler interface only. Do not call from within the RTS.
 218    --  This must be called by the compiler-generated code for an allocator if
 219    --  the allocated object contains tasks, if the allocator exits without
 220    --  calling Activate_Tasks for a given activation chains, as can happen if
 221    --  an exception occurs during initialization of the object.
 222    --
 223    --  This should be called ONLY for tasks created via an allocator. Recovery
 224    --  of storage for unactivated local task declarations is done by
 225    --  Complete_Master and Complete_Task.
 226    --
 227    --  We remove each task from Chain and All_Tasks_List before we free the
 228    --  storage of its ATCB.
 229    --
 230    --  In other places where we recover the storage of unactivated tasks, we
 231    --  need to clean out the entry queues, but here that should not be
 232    --  necessary, since these tasks should not have been visible to any other
 233    --  tasks, and so no task should be able to queue a call on their entries.
 234    --
 235    --  Just in case somebody misuses this subprogram, there is a check to
 236    --  verify this condition.
 237
 238    procedure Finalize_Global_Tasks;
 239    --  This should be called to complete the execution of the environment task
 240    --  and shut down the tasking runtime system. It is the equivalent of
 241    --  Complete_Task, but for the environment task.
 242    --
 243    --  The environment task must first call Complete_Master, to wait for user
 244    --  tasks that depend on library-level packages to terminate. It then calls
 245    --  Abort_Dependents to abort the "independent" library-level server tasks
 246    --  that are created implicitly by the RTS packages (signal and timer server
 247    --  tasks), and then waits for them to terminate. Then, it calls
 248    --  Vulnerable_Complete_Task.
 249    --
 250    --  It currently also executes the global finalization list, and then resets
 251    --  the "soft links".
 252
 253    procedure Free_Task (T : Task_ID);
 254    --  Recover all runtime system storage associated with the task T, but only
 255    --  if T has terminated. Do nothing in the other case. It is called from
 256    --  Unchecked_Deallocation, for objects that are or contain tasks.
 257
 258    function Terminated (T : Task_ID) return Boolean;
 259    --  This is called by the compiler to implement the 'Terminated attribute.
 260    --  Though is not required to be so by the ARM, we choose to synchronize
 261    --  with the task's ATCB, so that this is more useful for polling the state
 262    --  of a task, and so that it becomes an abort completion point for the
 263    --  calling task (via Undefer_Abort).
 264    --
 265    --  source code:
 266    --     T1'Terminated
 267    --
 268    --  code expansion:
 269    --     terminated (t1._task_id)
 270
 271    procedure Terminate_Task (Self_ID : Task_ID);
 272    --  Terminate the calling task.
 273    --  This should only be called by the Task_Wrapper procedure, and to
 274    --  deallocate storage associate with foreign tasks.
 275
 276 end System.Tasking.Stages;