s-taskin.ads: Minor comment fix.

2014-01-31  Bob Duff  <duff@adacore.com>

	* s-taskin.ads: Minor comment fix.
	* s-tassta.adb (Abort_Dependents): Don't abort all dependents;
	just direct dependents. If this is actually an abort, each task
	will take care of aborting its dependents, so all dependents will
	get aborted, as before. However, when this is called the second
	time from Vulnerable_Complete_Master "for convenience" (i.e. to
	kill off tasks waiting at terminate alternatives), aborting
	indirect dependents is wrong, because it causes some unrelated
	tasks to get aborted.

From-SVN: r207350

gcc/ada/ChangeLog

+2014-01-31  Bob Duff  <duff@adacore.com>
+
+	* s-taskin.ads: Minor comment fix.
+	* s-tassta.adb (Abort_Dependents): Don't abort all dependents;
+	just direct dependents. If this is actually an abort, each task
+	will take care of aborting its dependents, so all dependents will
+	get aborted, as before. However, when this is called the second
+	time from Vulnerable_Complete_Master "for convenience" (i.e. to
+	kill off tasks waiting at terminate alternatives), aborting
+	indirect dependents is wrong, because it causes some unrelated
+	tasks to get aborted.
+
 2014-01-31  Robert Dewar  <dewar@adacore.com>
 
 	* sem_ch4.adb: Minor reformatting.

gcc/ada/s-taskin.ads

@@ -754,7 +754,7 @@ package System.Tasking is
    subtype Master_ID is Master_Level;
 
    --  Normally, a task starts out with internal master nesting level one
-   --  larger than external master nesting level. It is incremented to one by
+   --  larger than external master nesting level. It is incremented by one by
    --  Enter_Master, which is called in the task body only if the compiler
    --  thinks the task may have dependent tasks. It is set to 1 for the
    --  environment task, the level 2 is reserved for server tasks of the

gcc/ada/s-tassta.adb

@@ -150,27 +150,28 @@ package body System.Tasking.Stages is
       C : Task_Id;
       P : Task_Id;
 
+      --  Each task C will take care of its own dependents, so there is no need
+      --  to worry about them here. In fact, it would be wrong to abort
+      --  indirect dependents here, because we can't distinguish between
+      --  duplicate master ids. For example, suppose we have three nested task
+      --  bodies T1,T2,T3. And suppose T1 also calls P which calls Q (and both
+      --  P and Q are task masters). Q will have the same master id as
+      --  Master_of_Task of T3. Previous versions of this would abort T3 when Q
+      --  calls Complete_Master, which was completely wrong.
+
    begin
       C := All_Tasks_List;
       while C /= null loop
          P := C.Common.Parent;
-         while P /= null loop
-            if P = Self_ID then
-
-               --  ??? C is supposed to take care of its own dependents, so
-               --  there should be no need to worry about them. Need to double
-               --  check this.
-
-               if C.Master_of_Task = Self_ID.Master_Within then
-                  Utilities.Abort_One_Task (Self_ID, C);
-                  C.Dependents_Aborted := True;
-               end if;
 
-               exit;
+         if P = Self_ID then
+            if C.Master_of_Task = Self_ID.Master_Within then
+               pragma Debug
+                 (Debug.Trace (Self_ID, "Aborting", 'X', C));
+               Utilities.Abort_One_Task (Self_ID, C);
+               C.Dependents_Aborted := True;
             end if;
-
-            P := P.Common.Parent;
-         end loop;
+         end if;
 
          C := C.Common.All_Tasks_Link;
       end loop;
@@ -715,6 +716,10 @@ package body System.Tasking.Stages is
       if Runtime_Traces then
          Send_Trace_Info (T_Create, T);
       end if;
+
+      pragma Debug
+        (Debug.Trace
+           (Self_ID, "Created task in " & T.Master_of_Task'Img, 'C', T));
    end Create_Task;
 
    --------------------
@@ -734,6 +739,9 @@ package body System.Tasking.Stages is
       Self_ID : constant Task_Id := STPO.Self;
    begin
       Self_ID.Master_Within := Self_ID.Master_Within + 1;
+      pragma Debug
+        (Debug.Trace
+           (Self_ID, "Enter_Master ->" & Self_ID.Master_Within'Img, 'M'));
    end Enter_Master;
 
    -------------------------------
@@ -1669,7 +1677,7 @@ package body System.Tasking.Stages is
 
    begin
       pragma Debug
-        (Debug.Trace (Self_ID, "V_Complete_Master", 'C'));
+        (Debug.Trace (Self_ID, "V_Complete_Master(" & CM'Img & ")", 'C'));
 
       pragma Assert (Self_ID.Common.Wait_Count = 0);
       pragma Assert
@@ -1712,7 +1720,7 @@ package body System.Tasking.Stages is
             Unlock (C);
          end if;
 
-         --  Count it if dependent on this master
+         --  Count it if directly dependent on this master
 
          if C.Common.Parent = Self_ID and then C.Master_of_Task = CM then
             Write_Lock (C);
@@ -1759,6 +1767,8 @@ package body System.Tasking.Stages is
                Write_Lock (Self_ID);
             end if;
          else
+            pragma Debug
+              (Debug.Trace (Self_ID, "master_completion_sleep", 'C'));
             Sleep (Self_ID, Master_Completion_Sleep);
          end if;
       end loop;