1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--               S Y S T E M . E X C E P T I O N _ T A B L E                --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--          Copyright (C) 1996-2014, Free Software Foundation, Inc.         --
10--                                                                          --
11-- GNAT 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-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32pragma Compiler_Unit_Warning;
33
34with System.Soft_Links; use System.Soft_Links;
35
36package body System.Exception_Table is
37
38   use System.Standard_Library;
39
40   type Hash_Val is mod 2 ** 8;
41   subtype Hash_Idx is Hash_Val range 1 .. 37;
42
43   HTable : array (Hash_Idx) of aliased Exception_Data_Ptr;
44   --  Actual hash table containing all registered exceptions
45   --
46   --  The table is very small and the hash function weak, as looking up
47   --  registered exceptions is rare and minimizing space and time overhead
48   --  of registration is more important. In addition, it is expected that the
49   --  exceptions that need to be looked up are registered dynamically, and
50   --  therefore will be at the begin of the hash chains.
51   --
52   --  The table differs from System.HTable.Static_HTable in that the final
53   --  element of each chain is not marked by null, but by a pointer to self.
54   --  This way it is possible to defend against the same entry being inserted
55   --  twice, without having to do a lookup which is relatively expensive for
56   --  programs with large number
57   --
58   --  All non-local subprograms use the global Task_Lock to protect against
59   --  concurrent use of the exception table. This is needed as local
60   --  exceptions may be declared concurrently with those declared at the
61   --  library level.
62
63   --  Local Subprograms
64
65   generic
66      with procedure Process (T : Exception_Data_Ptr; More : out Boolean);
67   procedure Iterate;
68   --  Iterate over all
69
70   function Lookup  (Name : String) return Exception_Data_Ptr;
71   --  Find and return the Exception_Data of the exception with the given Name
72   --  (which must be in all uppercase), or null if none was registered.
73
74   procedure Register (Item : Exception_Data_Ptr);
75   --  Register an exception with the given Exception_Data in the table.
76
77   function Has_Name (Item : Exception_Data_Ptr; Name : String) return Boolean;
78   --  Return True iff Item.Full_Name and Name are equal. Both names are
79   --  assumed to be in all uppercase and end with ASCII.NUL.
80
81   function Hash (S : String) return Hash_Idx;
82   --  Return the index in the hash table for S, which is assumed to be all
83   --  uppercase and end with ASCII.NUL.
84
85   --------------
86   -- Has_Name --
87   --------------
88
89   function Has_Name (Item : Exception_Data_Ptr; Name : String) return Boolean
90   is
91      S : constant Big_String_Ptr := To_Ptr (Item.Full_Name);
92      J : Integer := S'First;
93
94   begin
95      for K in Name'Range loop
96
97         --  Note that as both items are terminated with ASCII.NUL, the
98         --  comparison below must fail for strings of different lengths.
99
100         if S (J) /= Name (K) then
101            return False;
102         end if;
103
104         J := J + 1;
105      end loop;
106
107      return True;
108   end Has_Name;
109
110   ------------
111   -- Lookup --
112   ------------
113
114   function Lookup (Name : String) return Exception_Data_Ptr is
115      Prev   : Exception_Data_Ptr;
116      Curr   : Exception_Data_Ptr;
117
118   begin
119      Curr := HTable (Hash (Name));
120      Prev := null;
121      while Curr /= Prev loop
122         if Has_Name (Curr, Name) then
123            return Curr;
124         end if;
125
126         Prev := Curr;
127         Curr := Curr.HTable_Ptr;
128      end loop;
129
130      return null;
131   end Lookup;
132
133   ----------
134   -- Hash --
135   ----------
136
137   function Hash (S : String) return Hash_Idx is
138      Hash : Hash_Val := 0;
139
140   begin
141      for J in S'Range loop
142         exit when S (J) = ASCII.NUL;
143         Hash := Hash xor Character'Pos (S (J));
144      end loop;
145
146      return Hash_Idx'First + Hash mod (Hash_Idx'Last - Hash_Idx'First + 1);
147   end Hash;
148
149   -------------
150   -- Iterate --
151   -------------
152
153   procedure Iterate is
154      More : Boolean;
155      Prev, Curr : Exception_Data_Ptr;
156
157   begin
158      Outer : for Idx in HTable'Range loop
159         Prev   := null;
160         Curr   := HTable (Idx);
161
162         while Curr /= Prev loop
163               Process (Curr, More);
164
165               exit Outer when not More;
166
167               Prev := Curr;
168               Curr := Curr.HTable_Ptr;
169         end loop;
170      end loop Outer;
171   end Iterate;
172
173   --------------
174   -- Register --
175   --------------
176
177   procedure Register (Item : Exception_Data_Ptr) is
178   begin
179      if Item.HTable_Ptr = null then
180         Prepend_To_Chain : declare
181            Chain : Exception_Data_Ptr
182                      renames HTable (Hash (To_Ptr (Item.Full_Name).all));
183
184         begin
185            if Chain = null then
186               Item.HTable_Ptr := Item;
187            else
188               Item.HTable_Ptr := Chain;
189            end if;
190
191            Chain := Item;
192         end Prepend_To_Chain;
193      end if;
194   end Register;
195
196   -------------------------------
197   -- Get_Registered_Exceptions --
198   -------------------------------
199
200   procedure Get_Registered_Exceptions
201     (List : out Exception_Data_Array;
202      Last : out Integer)
203   is
204      procedure Get_One (Item : Exception_Data_Ptr; More : out Boolean);
205      --  Add Item to List (List'First .. Last) by first incrementing Last
206      --  and storing Item in List (Last). Last should be in List'First - 1
207      --  and List'Last.
208
209      procedure Get_All is new Iterate (Get_One);
210      --  Store all registered exceptions in List, updating Last
211
212      -------------
213      -- Get_One --
214      -------------
215
216      procedure Get_One (Item : Exception_Data_Ptr; More : out Boolean) is
217      begin
218         if Last < List'Last then
219            Last := Last + 1;
220            List (Last) := Item;
221            More := True;
222
223         else
224            More := False;
225         end if;
226      end Get_One;
227
228   begin
229      --  In this routine the invariant is that List (List'First .. Last)
230      --  contains the registered exceptions retrieved so far.
231
232      Last := List'First - 1;
233
234      Lock_Task.all;
235      Get_All;
236      Unlock_Task.all;
237   end Get_Registered_Exceptions;
238
239   ------------------------
240   -- Internal_Exception --
241   ------------------------
242
243   function Internal_Exception
244     (X                   : String;
245      Create_If_Not_Exist : Boolean := True) return Exception_Data_Ptr
246   is
247      --  If X was not yet registered and Create_if_Not_Exist is True,
248      --  dynamically allocate and register a new exception.
249
250      type String_Ptr is access all String;
251
252      Dyn_Copy : String_Ptr;
253      Copy     : aliased String (X'First .. X'Last + 1);
254      Result   : Exception_Data_Ptr;
255
256   begin
257      Lock_Task.all;
258
259      Copy (X'Range) := X;
260      Copy (Copy'Last) := ASCII.NUL;
261      Result := Lookup (Copy);
262
263      --  If unknown exception, create it on the heap. This is a legitimate
264      --  situation in the distributed case when an exception is defined
265      --  only in a partition
266
267      if Result = null and then Create_If_Not_Exist then
268         Dyn_Copy := new String'(Copy);
269
270         Result :=
271           new Exception_Data'
272             (Not_Handled_By_Others => False,
273              Lang                  => 'A',
274              Name_Length           => Copy'Length,
275              Full_Name             => Dyn_Copy.all'Address,
276              HTable_Ptr            => null,
277              Foreign_Data          => Null_Address,
278              Raise_Hook            => null);
279
280         Register (Result);
281      end if;
282
283      Unlock_Task.all;
284
285      return Result;
286   end Internal_Exception;
287
288   ------------------------
289   -- Register_Exception --
290   ------------------------
291
292   procedure Register_Exception (X : Exception_Data_Ptr) is
293   begin
294      Lock_Task.all;
295      Register (X);
296      Unlock_Task.all;
297   end Register_Exception;
298
299   ---------------------------------
300   -- Registered_Exceptions_Count --
301   ---------------------------------
302
303   function Registered_Exceptions_Count return Natural is
304      Count : Natural := 0;
305
306      procedure Count_Item (Item : Exception_Data_Ptr; More : out Boolean);
307      --  Update Count for given Item
308
309      procedure Count_Item (Item : Exception_Data_Ptr; More : out Boolean) is
310         pragma Unreferenced (Item);
311      begin
312         Count := Count + 1;
313         More := Count < Natural'Last;
314      end Count_Item;
315
316      procedure Count_All is new Iterate (Count_Item);
317
318   begin
319      Lock_Task.all;
320      Count_All;
321      Unlock_Task.all;
322
323      return Count;
324   end Registered_Exceptions_Count;
325
326begin
327   --  Register the standard exceptions at elaboration time
328
329   --  We don't need to use the locking version here as the elaboration
330   --  will not be concurrent and no tasks can call any subprograms of this
331   --  unit before it has been elaborated.
332
333   Register (Abort_Signal_Def'Access);
334   Register (Tasking_Error_Def'Access);
335   Register (Storage_Error_Def'Access);
336   Register (Program_Error_Def'Access);
337   Register (Numeric_Error_Def'Access);
338   Register (Constraint_Error_Def'Access);
339end System.Exception_Table;
340