Fix rare race condition in Dets

The correction is due to the the evil testcase
dets_SUITE:simultaneous_open(). If the process repairing a Dets file
is killed (should normally never happen), and another process tries to
repair the file, a temporary file from the first process could live on
for a while, even after a successful call to file:delete(). This has
only been seen on W-nd-ows, where it is a known problem.

There are other ways to deal with the problem (rename the file; use
some other filename), but we continue using one certain filename in
order to be as backwards compatible as possible.

2 files changed, 30 insertions, 13 deletions

diff --git a/lib/stdlib/src/dets.erl b/lib/stdlib/src/dets.erl
index 76e03bbfaa..a4bd45ea19 100644
--- a/lib/stdlib/src/dets.erl
+++ b/lib/stdlib/src/dets.erl
@@ -2839,17 +2839,22 @@ fsck_try(Fd, Tab, FH, Fname, SlotNumbers, Version) ->
 
 tempfile(Fname) ->
     Tmp = lists:concat([Fname, ".TMP"]),
-    tempfile(Tmp, 10).
-
-tempfile(Tmp, 0) ->
-    Tmp;
-tempfile(Tmp, N) ->
     case file:delete(Tmp) of
-        {error, eacces} -> % 'dets_process_died' happened anyway... (W-nd-ws)
-            timer:sleep(1000),
-            tempfile(Tmp, N-1);
-        _ ->
-            Tmp
+        {error, _Reason} -> % typically enoent
+            ok;
+        ok ->
+            assure_no_file(Tmp)
+    end,
+    Tmp.
+
+assure_no_file(File) ->
+    case file:read_file_info(File) of
+        {ok, _FileInfo} ->
+            %% Wait for some other process to close the file:
+            timer:sleep(100),
+            assure_no_file(File);
+        {error, _} ->
+            ok
     end.
 
 %% -> {ok, NewHead} | {try_again, integer()} | Error
diff --git a/lib/stdlib/src/dets_server.erl b/lib/stdlib/src/dets_server.erl
index 268c201047..3164d40f35 100644
--- a/lib/stdlib/src/dets_server.erl
+++ b/lib/stdlib/src/dets_server.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2001-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2001-2014. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -171,9 +171,15 @@ handle_info({pending_reply, {Ref, Result0}}, State) ->
 		link(Pid),
 		do_link(Store, FromPid),
 		true = ets:insert(Store, {FromPid, Tab}),
-		true = ets:insert(?REGISTRY, {Tab, 1, Pid}),
-		true = ets:insert(?OWNERS, {Pid, Tab}),
+                %% do_internal_open() has already done the following:
+                %% true = ets:insert(?REGISTRY, {Tab, 1, Pid}),
+                %% true = ets:insert(?OWNERS, {Pid, Tab}),
 		{ok, Tab};
+            {Reply, internal_open} ->
+                %% Clean up what do_internal_open() did:
+                true = ets:delete(?REGISTRY, Tab),
+                true = ets:delete(?OWNERS, Pid),
+                Reply;
 	    {Reply, _} -> % ok or Error
 		Reply
 	end,
@@ -309,6 +315,12 @@ do_internal_open(State, From, Args) ->
                       [T, _, _] -> T;
                       [_, _] -> Ref
                   end,
+            %% Pretend the table is open. If someone else tries to
+            %% open the file it will always become a pending
+            %% 'add_user' request. If someone tries to use the table
+            %% there will be a delay, but that is OK.
+            true = ets:insert(?REGISTRY, {Tab, 1, Pid}),
+            true = ets:insert(?OWNERS, {Pid, Tab}),
             pending_call(Tab, Pid, Ref, From, Args, internal_open, State);
         Error ->
             {Error, State}