1------------------------------------------------------------------------------
2--                                                                          --
3--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
4--                                                                          --
5--         S Y S T E M . T A S K I N G . I N I T I A L I Z A T I O N        --
6--                                                                          --
7--                                  S p e c                                 --
8--                                                                          --
9--          Copyright (C) 1992-2012, 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 3,  or (at your option) any later ver- --
14-- sion.  GNAT 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.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNARL was developed by the GNARL team at Florida State University.       --
28-- Extensive contributions were provided by Ada Core Technologies, Inc.     --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  This package provides overall initialization of the tasking portion of the
33--  RTS. This package must be elaborated before any tasking features are used.
34
35package System.Tasking.Initialization is
36
37   procedure Remove_From_All_Tasks_List (T : Task_Id);
38   --  Remove T from All_Tasks_List. Call this function with RTS_Lock taken
39
40   ---------------------------------
41   -- Tasking-Specific Soft Links --
42   ---------------------------------
43
44   --  These permit us to leave out certain portions of the tasking
45   --  run-time system if they are not used.  They are only used internally
46   --  by the tasking run-time system.
47
48   --  So far, the only example is support for Ada.Task_Attributes
49
50   type Proc_T is access procedure (T : Task_Id);
51
52   procedure Finalize_Attributes (T : Task_Id);
53   procedure Initialize_Attributes (T : Task_Id);
54
55   Finalize_Attributes_Link : Proc_T := Finalize_Attributes'Access;
56   --  should be called with abort deferred and T.L write-locked
57
58   Initialize_Attributes_Link : Proc_T := Initialize_Attributes'Access;
59   --  should be called with abort deferred, but holding no locks
60
61   -------------------------
62   -- Abort Defer/Undefer --
63   -------------------------
64
65   --  Defer_Abort defers the effects of low-level abort and priority change
66   --  in the calling task until a matching Undefer_Abort call is executed.
67
68   --  Undefer_Abort DOES MORE than just undo the effects of one call to
69   --  Defer_Abort. It is the universal "polling point" for deferred
70   --  processing, including the following:
71
72   --  1) base priority changes
73
74   --  2) abort/ATC
75
76   --  Abort deferral MAY be nested (Self_ID.Deferral_Level is a count), but
77   --  to avoid waste and undetected errors, it generally SHOULD NOT be
78   --  nested. The symptom of over-deferring abort is that an exception may
79   --  fail to be raised, or an abort may fail to take place.
80
81   --  Therefore, there are two sets of the inlineable defer/undefer routines,
82   --  which are the ones to be used inside GNARL. One set allows nesting. The
83   --  other does not. People who maintain the GNARL should try to avoid using
84   --  the nested versions, or at least look very critically at the places
85   --  where they are used.
86
87   --  In general, any GNARL call that is potentially blocking, or whose
88   --  semantics require that it sometimes raise an exception, or that is
89   --  required to be an abort completion point, must be made with abort
90   --  Deferral_Level = 1.
91
92   --  In general, non-blocking GNARL calls, which may be made from inside a
93   --  protected action, are likely to need to allow nested abort deferral.
94
95   --  With some critical exceptions (which are supposed to be documented),
96   --  internal calls to the tasking runtime system assume abort is already
97   --  deferred, and do not modify the deferral level.
98
99   --  There is also a set of non-inlineable defer/undefer routines, for direct
100   --  call from the compiler. These are not inlineable because they may need
101   --  to be called via pointers ("soft links"). For the sake of efficiency,
102   --  the version with Self_ID as parameter should used wherever possible.
103   --  These are all nestable.
104
105   --  Non-nestable inline versions
106
107   procedure Defer_Abort (Self_ID : Task_Id);
108   pragma Inline (Defer_Abort);
109
110   procedure Undefer_Abort (Self_ID : Task_Id);
111   pragma Inline (Undefer_Abort);
112
113   --  Nestable inline versions
114
115   procedure Defer_Abort_Nestable (Self_ID : Task_Id);
116   pragma Inline (Defer_Abort_Nestable);
117
118   procedure Undefer_Abort_Nestable (Self_ID : Task_Id);
119   pragma Inline (Undefer_Abort_Nestable);
120
121   procedure Do_Pending_Action (Self_ID : Task_Id);
122   --  Only call with no locks, and when Self_ID.Pending_Action = True Perform
123   --  necessary pending actions (e.g. abort, priority change). This procedure
124   --  is usually called when needed as a result of calling Undefer_Abort,
125   --  although in the case of e.g. No_Abort restriction, it can be necessary
126   --  to force execution of pending actions.
127
128   function Check_Abort_Status return Integer;
129   --  Returns Boolean'Pos (True) iff abort signal should raise
130   --  Standard'Abort_Signal. Only used by IRIX currently.
131
132   --------------------------
133   -- Change Base Priority --
134   --------------------------
135
136   procedure Change_Base_Priority (T : Task_Id);
137   --  Change the base priority of T. Has to be called with the affected
138   --  task's ATCB write-locked. May temporarily release the lock.
139
140   ----------------------
141   -- Task Lock/Unlock --
142   ----------------------
143
144   procedure Task_Lock (Self_ID : Task_Id);
145   pragma Inline (Task_Lock);
146
147   procedure Task_Unlock (Self_ID : Task_Id);
148   pragma Inline (Task_Unlock);
149   --  These are versions of Lock_Task and Unlock_Task created for use
150   --  within the GNARL.
151
152   procedure Final_Task_Unlock (Self_ID : Task_Id);
153   --  This version is only for use in Terminate_Task, when the task is
154   --  relinquishing further rights to its own ATCB. There is a very
155   --  interesting potential race condition there, where the old task may run
156   --  concurrently with a new task that is allocated the old tasks (now
157   --  reused) ATCB. The critical thing here is to not make any reference to
158   --  the ATCB after the lock is released. See also comments on
159   --  Terminate_Task and Unlock.
160
161   procedure Wakeup_Entry_Caller
162     (Self_ID    : Task_Id;
163      Entry_Call : Entry_Call_Link;
164      New_State  : Entry_Call_State);
165   pragma Inline (Wakeup_Entry_Caller);
166   --  This is called at the end of service of an entry call, to abort the
167   --  caller if he is in an abortable part, and to wake up the caller if he
168   --  is on Entry_Caller_Sleep. Call it holding the lock of Entry_Call.Self.
169   --
170   --  Timed_Call or Simple_Call:
171   --    The caller is waiting on Entry_Caller_Sleep, in Wait_For_Completion,
172   --    or Wait_For_Completion_With_Timeout.
173   --
174   --  Conditional_Call:
175   --    The caller might be in Wait_For_Completion,
176   --    waiting for a rendezvous (possibly requeued without abort) to
177   --    complete.
178   --
179   --  Asynchronous_Call:
180   --    The caller may be executing in the abortable part an async. select,
181   --    or on a time delay, if Entry_Call.State >= Was_Abortable.
182
183   procedure Locked_Abort_To_Level
184     (Self_ID : Task_Id;
185      T       : Task_Id;
186      L       : ATC_Level);
187   pragma Inline (Locked_Abort_To_Level);
188   --  Abort a task to a specified ATC level. Call this only with T locked
189
190end System.Tasking.Initialization;
191