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Comment:cron: fix incorrect concurrent access to Event_List internals
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: ffb7e43a74c49d02035a996c333aa7a4ecf9389d
User & Date: nat on 2017-04-13 20:30:01
Other Links: manifest | tags
Context
2017-05-05
19:50
s_expressions-parsers-tests: fix alphabetical ordering of tests check-in: a76936f058 user: nat tags: trunk
2017-04-13
20:30
cron: fix incorrect concurrent access to Event_List internals check-in: ffb7e43a74 user: nat tags: trunk
2017-04-12
20:54
cron-tests: new test to show an issue with unsafe access to Event_List

Thanks to OpenBSD for providing an environment where this issue could happen accidentally. Now to find a fix... check-in: 3267d1247d user: nat tags: trunk

Changes

Modified src/natools-cron.adb from [7158082d55] to [e86553a260].

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------------------------------------------------------------------------------
-- Copyright (c) 2014-2015, Natacha Porté                                   --
-- Copyright (c) 2014-2017, Natacha Porté                                   --
--                                                                          --
-- Permission to use, copy, modify, and distribute this software for any    --
-- purpose with or without fee is hereby granted, provided that the above   --
-- copyright notice and this permission notice appear in all copies.        --
--                                                                          --
-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES --
-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF         --
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         else
            Callback := Callback_Refs.Null_Reference;
         end if;

         First_Changed := False;
      end Get_First;


      procedure Get_Event_List
        (Source : in Event_List;
         List : out Event_Lists.List) is
      begin
         List := Source.List;
      end Get_Event_List;


      entry Update_Notification when First_Changed is
      begin
         null;
      end Update_Notification;

   end Database;
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   ----------------
   -- Event List --
   ----------------

   overriding procedure Run (Self : in out Event_List) is
      Local_List : Event_Lists.List;
   begin
      Database.Get_Event_List (Self, Local_List);

      for Ref of Self.List loop
      for Ref of Local_List loop
         Ref.Update.Data.Run;
      end loop;
   end Run;


   procedure Append
     (Self : in out Event_List;

Modified src/natools-cron.ads from [503d6dd125] to [de34f4fcac].

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------------------------------------------------------------------------------
-- Copyright (c) 2014-2015, Natacha Porté                                   --
-- Copyright (c) 2014-2017, Natacha Porté                                   --
--                                                                          --
-- Permission to use, copy, modify, and distribute this software for any    --
-- purpose with or without fee is hereby granted, provided that the above   --
-- copyright notice and this permission notice appear in all copies.        --
--                                                                          --
-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES --
-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF         --
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   type Cron_Entry is new Ada.Finalization.Limited_Controlled with record
      Callback : Callback_Refs.Reference;
   end record;

   overriding procedure Finalize (Object : in out Cron_Entry);


   package Event_Lists is new Ada.Containers.Doubly_Linked_Lists
     (Callback_Refs.Reference, Callback_Refs."=");

   type Event_List is new Callback with record
      List : Event_Lists.List;
   end record;

   overriding procedure Run (Self : in out Event_List);
      --  Sequentially run the contained events

   procedure Append
     (Self : in out Event_List;
      Ref : in Callback_Refs.Reference);
      --  Append Ref at the end of Self.List

   procedure Remove
     (Self : in out Event_List;
      Ref : in Callback_Refs.Reference;
      Removed : out Boolean);
      --  Remove Ref from Self.List, through a linear search

   function Is_Empty (Self : Event_List) return Boolean;
      --  Return whether Self contains any element


   function "<" (Left, Right : Periodic_Time) return Boolean;
      --  Comparison function for ordered map

   package Entry_Maps is new Ada.Containers.Ordered_Maps
     (Periodic_Time, Callback_Refs.Reference, "<", Callback_Refs."=");

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      procedure Get_First
        (Time : out Periodic_Time;
         Callback : out Callback_Refs.Reference);
         --  Return the next active callback, or an empty reference when
         --  the database is empty (to signal task termination).

      procedure Get_Event_List
        (Source : in Event_List;
         List : out Event_Lists.List);
         --  Initialize an event list from Source without
         --  any concurrent tampering of the list.

      entry Update_Notification;
         --  Block as long as the next active item does not change

   private
      Map : Entry_Maps.Map;
      First_Changed : Boolean := False;
   end Database;

   task type Worker is
   end Worker;

   type Worker_Access is access Worker;

   procedure Unchecked_Free is new Ada.Unchecked_Deallocation
     (Worker, Worker_Access);

   Global_Worker : Worker_Access := null;


   package Event_Lists is new Ada.Containers.Doubly_Linked_Lists
     (Callback_Refs.Reference, Callback_Refs."=");

   type Event_List is new Callback with record
      List : Event_Lists.List;
   end record;

   overriding procedure Run (Self : in out Event_List);
      --  Sequentially run the contained events

   procedure Append
     (Self : in out Event_List;
      Ref : in Callback_Refs.Reference);
      --  Append Ref at the end of Self.List

   procedure Remove
     (Self : in out Event_List;
      Ref : in Callback_Refs.Reference;
      Removed : out Boolean);
      --  Remove Ref from Self.List, through a linear search

   function Is_Empty (Self : Event_List) return Boolean;
      --  Return whether Self contains any element

end Natools.Cron;