1------------------------------------------------------------------------------
2--                                                                          --
3--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
4--                                                                          --
5--      S Y S T E M . T A S K I N G . P R O T E C T E D _ O B J E C T S     --
6--                                                                          --
7--                                  B o d y                                 --
8--                                                                          --
9--            Copyright (C) 1991-2017, Florida State University             --
10--                     Copyright (C) 1995-2018, AdaCore                     --
11--                                                                          --
12-- GNAT 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 3,  or (at your option) any later ver- --
15-- sion.  GNAT 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.                                     --
18--                                                                          --
19-- As a special exception under Section 7 of GPL version 3, you are granted --
20-- additional permissions described in the GCC Runtime Library Exception,   --
21-- version 3.1, as published by the Free Software Foundation.               --
22--                                                                          --
23-- You should have received a copy of the GNU General Public License and    --
24-- a copy of the GCC Runtime Library Exception along with this program;     --
25-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
26-- <http://www.gnu.org/licenses/>.                                          --
27--                                                                          --
28-- GNARL was developed by the GNARL team at Florida State University.       --
29-- Extensive contributions were provided by Ada Core Technologies, Inc.     --
30--                                                                          --
31------------------------------------------------------------------------------
32
33pragma Polling (Off);
34--  Turn off polling, we do not want ATC polling to take place during tasking
35--  operations. It causes infinite loops and other problems.
36
37with System.Task_Primitives.Operations;
38with System.Soft_Links.Tasking;
39
40with System.Secondary_Stack;
41pragma Elaborate_All (System.Secondary_Stack);
42pragma Unreferenced (System.Secondary_Stack);
43--  Make sure the body of Secondary_Stack is elaborated before calling
44--  Init_Tasking_Soft_Links. See comments for this routine for explanation.
45
46package body System.Tasking.Protected_Objects is
47
48   use System.Task_Primitives.Operations;
49
50   ----------------
51   -- Local Data --
52   ----------------
53
54   Locking_Policy : Character;
55   pragma Import (C, Locking_Policy, "__gl_locking_policy");
56
57   -------------------------
58   -- Finalize_Protection --
59   -------------------------
60
61   procedure Finalize_Protection (Object : in out Protection) is
62   begin
63      Finalize_Lock (Object.L'Unrestricted_Access);
64   end Finalize_Protection;
65
66   ---------------------------
67   -- Initialize_Protection --
68   ---------------------------
69
70   procedure Initialize_Protection
71     (Object           : Protection_Access;
72      Ceiling_Priority : Integer)
73   is
74      Init_Priority : Integer := Ceiling_Priority;
75
76   begin
77      if Init_Priority = Unspecified_Priority then
78         Init_Priority := System.Priority'Last;
79      end if;
80
81      Initialize_Lock (Init_Priority, Object.L'Access);
82      Object.Ceiling := System.Any_Priority (Init_Priority);
83      Object.New_Ceiling := System.Any_Priority (Init_Priority);
84      Object.Owner := Null_Task;
85   end Initialize_Protection;
86
87   -----------------
88   -- Get_Ceiling --
89   -----------------
90
91   function Get_Ceiling
92     (Object : Protection_Access) return System.Any_Priority is
93   begin
94      return Object.New_Ceiling;
95   end Get_Ceiling;
96
97   ----------
98   -- Lock --
99   ----------
100
101   procedure Lock (Object : Protection_Access) is
102      Ceiling_Violation : Boolean;
103
104   begin
105      --  The lock is made without deferring abort
106
107      --  Therefore the abort has to be deferred before calling this routine.
108      --  This means that the compiler has to generate a Defer_Abort call
109      --  before the call to Lock.
110
111      --  The caller is responsible for undeferring abort, and compiler
112      --  generated calls must be protected with cleanup handlers to ensure
113      --  that abort is undeferred in all cases.
114
115      --  If pragma Detect_Blocking is active then, as described in the ARM
116      --  9.5.1, par. 15, we must check whether this is an external call on a
117      --  protected subprogram with the same target object as that of the
118      --  protected action that is currently in progress (i.e., if the caller
119      --  is already the protected object's owner). If this is the case hence
120      --  Program_Error must be raised.
121
122      if Detect_Blocking and then Object.Owner = Self then
123         raise Program_Error;
124      end if;
125
126      Write_Lock (Object.L'Access, Ceiling_Violation);
127
128      if Ceiling_Violation then
129         raise Program_Error;
130      end if;
131
132      --  We are entering in a protected action, so that we increase the
133      --  protected object nesting level (if pragma Detect_Blocking is
134      --  active), and update the protected object's owner.
135
136      if Detect_Blocking then
137         declare
138            Self_Id : constant Task_Id := Self;
139         begin
140            --  Update the protected object's owner
141
142            Object.Owner := Self_Id;
143
144            --  Increase protected object nesting level
145
146            Self_Id.Common.Protected_Action_Nesting :=
147              Self_Id.Common.Protected_Action_Nesting + 1;
148         end;
149      end if;
150   end Lock;
151
152   --------------------
153   -- Lock_Read_Only --
154   --------------------
155
156   procedure Lock_Read_Only (Object : Protection_Access) is
157      Ceiling_Violation : Boolean;
158
159   begin
160      --  If pragma Detect_Blocking is active then, as described in the ARM
161      --  9.5.1, par. 15, we must check whether this is an external call on
162      --  protected subprogram with the same target object as that of the
163      --  protected action that is currently in progress (i.e., if the caller
164      --  is already the protected object's owner). If this is the case hence
165      --  Program_Error must be raised.
166      --
167      --  Note that in this case (getting read access), several tasks may have
168      --  read ownership of the protected object, so that this method of
169      --  storing the (single) protected object's owner does not work reliably
170      --  for read locks. However, this is the approach taken for two major
171      --  reasons: first, this function is not currently being used (it is
172      --  provided for possible future use), and second, it largely simplifies
173      --  the implementation.
174
175      if Detect_Blocking and then Object.Owner = Self then
176         raise Program_Error;
177      end if;
178
179      Read_Lock (Object.L'Access, Ceiling_Violation);
180
181      if Ceiling_Violation then
182         raise Program_Error;
183      end if;
184
185      --  We are entering in a protected action, so we increase the protected
186      --  object nesting level (if pragma Detect_Blocking is active).
187
188      if Detect_Blocking then
189         declare
190            Self_Id : constant Task_Id := Self;
191         begin
192            --  Update the protected object's owner
193
194            Object.Owner := Self_Id;
195
196            --  Increase protected object nesting level
197
198            Self_Id.Common.Protected_Action_Nesting :=
199              Self_Id.Common.Protected_Action_Nesting + 1;
200         end;
201      end if;
202   end Lock_Read_Only;
203
204   -----------------
205   -- Set_Ceiling --
206   -----------------
207
208   procedure Set_Ceiling
209     (Object : Protection_Access;
210      Prio   : System.Any_Priority) is
211   begin
212      Object.New_Ceiling := Prio;
213   end Set_Ceiling;
214
215   ------------
216   -- Unlock --
217   ------------
218
219   procedure Unlock (Object : Protection_Access) is
220   begin
221      --  We are exiting from a protected action, so that we decrease the
222      --  protected object nesting level (if pragma Detect_Blocking is
223      --  active), and remove ownership of the protected object.
224
225      if Detect_Blocking then
226         declare
227            Self_Id : constant Task_Id := Self;
228
229         begin
230            --  Calls to this procedure can only take place when being within
231            --  a protected action and when the caller is the protected
232            --  object's owner.
233
234            pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
235                             and then Object.Owner = Self_Id);
236
237            --  Remove ownership of the protected object
238
239            Object.Owner := Null_Task;
240
241            --  We are exiting from a protected action, so we decrease the
242            --  protected object nesting level.
243
244            Self_Id.Common.Protected_Action_Nesting :=
245              Self_Id.Common.Protected_Action_Nesting - 1;
246         end;
247      end if;
248
249      --  Before releasing the mutex we must actually update its ceiling
250      --  priority if it has been changed.
251
252      if Object.New_Ceiling /= Object.Ceiling then
253         if Locking_Policy = 'C' then
254            System.Task_Primitives.Operations.Set_Ceiling
255              (Object.L'Access, Object.New_Ceiling);
256         end if;
257
258         Object.Ceiling := Object.New_Ceiling;
259      end if;
260
261      Unlock (Object.L'Access);
262
263   end Unlock;
264
265begin
266   --  Ensure that tasking is initialized, as well as tasking soft links
267   --  when using protected objects.
268
269   Tasking.Initialize;
270   System.Soft_Links.Tasking.Init_Tasking_Soft_Links;
271end System.Tasking.Protected_Objects;
272