base: Fix DCHECK when thread creation fails

base/message_loop/message_loop.cc

 // Copyright 2013 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.
 
 #include "base/message_loop/message_loop.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 117 matching lines @@
 }
 
 MessageLoop::MessageLoop(scoped_ptr<MessagePump> pump)
     : MessageLoop(TYPE_CUSTOM, Bind(&ReturnPump, Passed(&pump))) {
   BindToCurrentThread();
 }
 
 MessageLoop::~MessageLoop() {
   // current() could be NULL if this message loop is destructed before it is
   // bound to a thread.
-  DCHECK(current() == this || !current());
+  DCHECK(current() == this || !pump_);

[danakj, 2016/01/05 19:40:15]

This no longer captures that current() is either |this| or |nullptr| though, but
the comment claims current() would be NULL otherwise.

I believe that this comment is wrong and current() may be some other message
loop if pump_ is not set which means BindToCurrentThread() was never called for
this MessageLoop yet. Can you confirm and fix the comment?

[Sami, 2016/01/06 10:56:19]

You're right, I just noticed the same thing while adding a test. I think the
main scenarios are:

1) The loop has been bound and is the current one.
2) The loop hasn't been bound and there is another current loop.
3) The loop hasn't been bound and there's no other loop either.

I've changed the comment and the logic accordingly.

 
   // iOS just attaches to the loop, it doesn't Run it.
   // TODO(stuartmorgan): Consider wiring up a Detach().
 #if !defined(OS_IOS)
   DCHECK(!run_loop_);
 #endif
 
 #if defined(OS_WIN)
   if (in_high_res_mode_)
     Time::ActivateHighResolutionTimer(false);
@@ skipping 605 matching lines @@
       persistent,
       mode,
       controller,
       delegate);
 }
 #endif
 
 #endif  // !defined(OS_NACL_SFI)
 
 }  // namespace base