/usr/share/ada/adainclude/gnatcoll/gnatcoll-refcount.adb is in libgnatcoll16.1.0-dev 17.0.2017-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 | ------------------------------------------------------------------------------
-- G N A T C O L L --
-- --
-- Copyright (C) 2010-2017, AdaCore --
-- --
-- This library is free software; you can redistribute it and/or modify it --
-- under terms of the GNU General Public License as published by the Free --
-- Software Foundation; either version 3, or (at your option) any later --
-- version. This library is distributed in the hope that it will be useful, --
-- but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHAN- --
-- TABILITY or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- --
-- --
-- --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
------------------------------------------------------------------------------
-- Notes on the implementation of weak pointers:
-- There are several ways in which a weak pointer can be implemented:
-- - Using two counters (one for full references, one for weak). When both
-- reach 0, the memory blocks is freed; when only the first reaches 0,
-- the element is released, and the block can be resized.
-- This is hard to make task safe without using critical section though.
-- - store a doubly-linked list of weak pointers along with the counter.
-- When the counter reaches 0, change each of the weak pointers to null.
-- This requires more memory.
-- - (our choice) make the weak pointer a smart pointer pointing to the
-- same data:
-- smart_ptr ---> chunk1: counter + element + pointer to chunk2
-- weak_ptr ---> chunk2: weak_counter + pointer to chunk1
pragma Ada_2012;
with Ada.Finalization; use Ada.Finalization;
with Ada.Unchecked_Conversion;
with Ada.Unchecked_Deallocation;
with GNATCOLL.Atomic; use GNATCOLL.Atomic;
with System.Memory; use System, System.Memory;
package body GNATCOLL.Refcount is
procedure Inc_Ref (R : access Counters; Atomic : Boolean)
with Inline => True;
procedure Inc_Ref (R : access Weak_Data; Atomic : Boolean)
with Inline => True;
-- Increase/Decrease the refcount, and return the new value
procedure Unchecked_Free is new Ada.Unchecked_Deallocation
(Weak_Data, Weak_Data_Access);
procedure Unchecked_Free is new Ada.Unchecked_Deallocation
(Refcounted'Class, Refcounted_Access);
procedure Finalize (Data : in out Weak_Data_Access; Atomic : Boolean);
-- Decrease refcount, and free memory if needed
function Sync_Bool_Compare_And_Swap
is new GNATCOLL.Atomic.Sync_Bool_Compare_And_Swap
(Weak_Data, Weak_Data_Access);
-------------
-- Inc_Ref --
-------------
procedure Inc_Ref (R : access Counters; Atomic : Boolean) is
begin
if Atomic then
Increment (R.Refcount);
else
Unsafe_Increment (R.Refcount);
end if;
end Inc_Ref;
procedure Inc_Ref (R : access Weak_Data; Atomic : Boolean) is
begin
if Atomic then
Increment (R.Refcount);
else
Unsafe_Increment (R.Refcount);
end if;
end Inc_Ref;
--------------
-- Finalize --
--------------
procedure Finalize (Data : in out Weak_Data_Access; Atomic : Boolean) is
begin
if Atomic then
if Decrement (Data.Refcount) then
Unchecked_Free (Data);
end if;
else
if Unsafe_Decrement (Data.Refcount) then
Unchecked_Free (Data);
end if;
end if;
Data := null;
end Finalize;
---------------------
-- Shared_Pointers --
---------------------
package body Shared_Pointers is
use type Pools.Element_Access;
procedure Unchecked_Free is new Ada.Unchecked_Deallocation
(Element_Type, Pools.Element_Access);
pragma Warnings (Off, "*possible aliasing problem*");
function Convert is new Ada.Unchecked_Conversion
(Pools.Element_Access, System.Address);
function Convert is new Ada.Unchecked_Conversion
(System.Address, Pools.Element_Access);
pragma Warnings (On, "*possible aliasing problem*");
---------
-- Set --
---------
procedure Set (Self : in out Ref'Class; Data : Element_Type) is
R : access Counters;
begin
Finalize (Self);
Self.Data := new Element_Type'(Data); -- uses storage pool
R := Pools.Header_Of (Self.Data);
R.Refcount := 1;
R.Weak_Data := null;
end Set;
-------------------
-- Unchecked_Get --
-------------------
function Unchecked_Get (Self : Ref'Class) return Element_Access is
begin
return Self.Data;
end Unchecked_Get;
-------------
-- Process --
-------------
procedure Process
(Self : Ref'Class;
Process : not null access procedure (E : Element_Type)) is
begin
Process (Self.Data.all);
end Process;
-------------
-- Is_Null --
-------------
function Is_Null (Self : Ref'Class) return Boolean is
begin
return Self.Data = null;
end Is_Null;
----------
-- Weak --
----------
function Weak (Self : Ref'Class) return Weak_Ref is
R : access Counters;
V : Weak_Data_Access;
begin
if Self.Data = null then
return Null_Weak_Ref;
end if;
R := Pools.Header_Of (Self.Data);
if R.Weak_Data = null then
V := new Weak_Data'
(Refcount => 2, -- hold by Self and the result
Element => Convert (Self.Data));
if not Sync_Bool_Compare_And_Swap
(R.Weak_Data'Access, Oldval => null, Newval => V)
then
-- Was set by another thread concurrently
Unchecked_Free (V);
-- Need to increase refcount for the old weak ref
Inc_Ref (R.Weak_Data, Atomic_Counters);
end if;
else
Inc_Ref (R.Weak_Data, Atomic_Counters);
end if;
return (Controlled with Data => R.Weak_Data);
end Weak;
---------
-- Set --
---------
procedure Set (Self : in out Ref'Class; Weak : Weak_Ref'Class) is
begin
Finalize (Self);
if not Weak.Was_Freed then
Self.Data := Convert (Weak.Data.Element);
Inc_Ref (Pools.Header_Of (Self.Data), Atomic_Counters);
end if;
end Set;
---------------
-- Was_Freed --
---------------
function Was_Freed (Self : Weak_Ref'Class) return Boolean is
begin
return Self.Data = null
or else Self.Data.Element = System.Null_Address;
end Was_Freed;
---------
-- "=" --
---------
overriding function "=" (P1, P2 : Ref) return Boolean is
begin
return P1.Data = P2.Data;
end "=";
------------
-- Adjust --
------------
overriding procedure Adjust (Self : in out Ref) is
begin
if Self.Data /= null then
Inc_Ref (Pools.Header_Of (Self.Data), Atomic_Counters);
end if;
end Adjust;
------------
-- Adjust --
------------
overriding procedure Adjust (Self : in out Weak_Ref) is
begin
if Self.Data /= null then
Inc_Ref (Self.Data, Atomic_Counters);
end if;
end Adjust;
--------------
-- Finalize --
--------------
overriding procedure Finalize (Self : in out Weak_Ref) is
Data : Weak_Data_Access := Self.Data;
begin
if Data /= null then
Self.Data := null;
Finalize (Data, Atomic_Counters);
end if;
end Finalize;
--------------
-- Finalize --
--------------
overriding procedure Finalize (Self : in out Ref) is
R : access Counters;
Data : Pools.Element_Access := Self.Data;
Tmp : Boolean;
begin
if Data /= null then
Self.Data := null;
R := Pools.Header_Of (Data);
if Atomic_Counters then
Tmp := Decrement (R.Refcount);
else
Tmp := Unsafe_Decrement (R.Refcount);
end if;
if Tmp then
if R.Weak_Data /= null then
R.Weak_Data.Element := System.Null_Address;
Finalize (R.Weak_Data, Atomic_Counters);
end if;
Release (Data.all);
Unchecked_Free (Data); -- using storage_pool
end if;
end if;
end Finalize;
------------------
-- Get_Refcount --
------------------
function Get_Refcount (Self : Ref'Class) return Natural is
begin
if Self.Data = null then
return 0;
else
return Natural (Pools.Header_Of (Self.Data).Refcount);
end if;
end Get_Refcount;
------------------
-- From_Element --
------------------
procedure From_Element
(Self : out Ref'Class; Element : Element_Access) is
begin
if Self.Data /= Element then
Finalize (Self);
Self.Data := Element;
Adjust (Self);
end if;
end From_Element;
end Shared_Pointers;
--------------------
-- Smart_Pointers --
--------------------
package body Smart_Pointers is
---------
-- Set --
---------
procedure Set (Self : in out Ref; Data : access Encapsulated'Class) is
begin
if Self.Data = Refcounted_Access (Data) then
-- Avoid finalizing Self.Data if we are going to reuse it
return;
end if;
Finalize (Self); -- decrement reference count
Self.Data := Refcounted_Access (Data);
Adjust (Self); -- increment reference count if needed
end Set;
---------
-- Set --
---------
procedure Set (Self : in out Ref; Data : Encapsulated'Class) is
Tmp : constant Encapsulated_Access := new Encapsulated'Class'(Data);
begin
Set (Self, Tmp);
end Set;
---------
-- Get --
---------
function Get (P : Ref) return Encapsulated_Access is
begin
return Encapsulated_Access (P.Data);
end Get;
---------
-- "=" --
---------
overriding function "=" (P1, P2 : Ref) return Boolean is
begin
return P1.Data = P2.Data;
end "=";
--------------
-- Finalize --
--------------
overriding procedure Finalize (P : in out Ref) is
Data : Refcounted_Access := P.Data;
begin
-- Make Finalize idempotent, since it could be called several
-- times for the same instance (RM 7.6.1(24)).
P.Data := null;
-- Test if refcount is > 0, in case we are already freeing this
-- element.
if Data /= null then
if Decrement (Data.Refcount) then
Free (Data.all);
Unchecked_Free (Data);
end if;
end if;
end Finalize;
------------
-- Adjust --
------------
overriding procedure Adjust (P : in out Ref) is
begin
if P.Data /= null then
Sync_Add_And_Fetch (P.Data.Refcount'Access, 1);
end if;
end Adjust;
------------------
-- Get_Refcount --
------------------
function Get_Refcount (Self : Ref) return Natural is
begin
if Self.Data = null then
return 0;
else
return Natural (Self.Data.Refcount);
end if;
end Get_Refcount;
end Smart_Pointers;
end GNATCOLL.Refcount;
|