[Ada] Warn on barrier functions that depend on global data

[Arnaud Charlet <charlet at adacore dot com>]

This patch adds a warning to a barrier function in an entry body, when the
barrier mentions data that is not private to the protected object, and subject
to external modification by unsynchronized actions, which can lead to hard-to-
diagnose race conditions.

Compiling entry_with_global_barrier.adb must yield

entry_with_global_barrier.adb:39:49:
         warning: potentially unsynchronized barrier
entry_with_global_barrier.adb:39:49:
         warning: "Global_Flag" should be private component of type


with Ada.Text_IO; use Ada.Text_IO;
procedure Entry_with_global_barrier is
   Global_Flag : Boolean := False;

   protected Triggered_from_Outside is
      entry Block_until_External_Condition;
   private
      Some_Flag : Boolean := False;
   end Triggered_from_Outside;

   protected body Triggered_from_Outside is

      entry Block_until_External_Condition when Global_Flag is
      begin
         Put_Line ("Barrier opened");
      end Block_until_External_Condition;

   end Triggered_from_Outside;

   task Block;
   task body Block is
   begin
      Triggered_from_Outside.Block_until_External_Condition;
      Put_Line ("Block task terminates");
   end Block;

begin
   Global_Flag := True;
   Put_Line ("Main task waits for termination");
end Entry_with_global_barrier;

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-01-31  Ed Schonberg  <schonberg@adacore.com>

	* exp_ch9.adb (Expand_Entry_Barrier): Warn if the barrier
	depends on data that is not private to the protected object,
	and potentially modifiable in unsynchronized fashion.

Attachment: difs
Description: Text document