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