Fixing AutoReset to be a template.

I've run into a couple of times this week when I needed one of these, for two different types besides bool.  Time to fix the TODO.

TEST=trybots FTW, and built locally.
BUG=none

Review URL: http://codereview.chromium.org/2394001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@48644 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 15 insertions, 12 deletions

diff --git a/base/auto_reset.h b/base/auto_reset.h
index dd968ef..3925abe 100644
--- a/base/auto_reset.h
+++ b/base/auto_reset.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -7,27 +7,30 @@
 
 #include "base/basictypes.h"
 
-// AutoReset is useful for setting a variable to some value only during a
-// particular scope.  If you have code that has to add "var = false;" or
-// "var = old_var;" at all the exit points of a block, for example, you would
-// benefit from using this instead.
+// AutoResetValue is useful for setting a variable to some value only
+// during a particular scope.  If you have code that has to add "var =
+// false;" or "var = old_var;" at all the exit points of a block, for
+// example, you would benefit from using this instead.
 //
-// NOTE: Right now this is hardcoded to work on bools, since that covers all the
-// cases where we've used it.  It would be reasonable to turn it into a template
-// class in the future.
+// This should be obvious, but note that the AutoResetValue instance
+// should have a shorter lifetime than the scoped_variable, to prevent
+// writing to invalid memory when the AutoResetValue goes out of
+// scope.
 
+template<typename T>
 class AutoReset {
  public:
-  explicit AutoReset(bool* scoped_variable, bool new_value)
+  AutoReset(T* scoped_variable, T new_value)
       : scoped_variable_(scoped_variable),
         original_value_(*scoped_variable) {
     *scoped_variable_ = new_value;
   }
+
   ~AutoReset() { *scoped_variable_ = original_value_; }
 
  private:
-  bool* scoped_variable_;
-  bool original_value_;
+  T* scoped_variable_;
+  T original_value_;
 
   DISALLOW_COPY_AND_ASSIGN(AutoReset);
 };
diff --git a/base/message_pump_libevent.cc b/base/message_pump_libevent.cc
index 01ebee5..2ad1d97 100644
--- a/base/message_pump_libevent.cc
+++ b/base/message_pump_libevent.cc
@@ -229,7 +229,7 @@ static void timer_callback(int fd, short events, void *context)
 // Reentrant!
 void MessagePumpLibevent::Run(Delegate* delegate) {
   DCHECK(keep_running_) << "Quit must have been called outside of Run!";
-  AutoReset auto_reset_in_run(&in_run_, true);
+  AutoReset<bool> auto_reset_in_run(&in_run_, true);
 
   // event_base_loopexit() + EVLOOP_ONCE is leaky, see http://crbug.com/25641.
   // Instead, make our own timer and reuse it on each call to event_base_loop().