ImportantFileWriter: check return value of PostTask...

chrome/browser/extensions/test_extension_prefs.cc

Index: chrome/browser/extensions/test_extension_prefs.cc
===================================================================
--- chrome/browser/extensions/test_extension_prefs.cc	(revision 77440)
+++ chrome/browser/extensions/test_extension_prefs.cc	(working copy)
@@ -65,10 +65,8 @@
     // The PrefService writes its persistent file on the file thread, so we
     // need to wait for any pending I/O to complete before creating a new
     // PrefService.
-    MessageLoop file_loop;
-    BrowserThread file_thread(BrowserThread::FILE, &file_loop);
     pref_service_->SavePersistentPrefs();
-    file_loop.RunAllPending();
+    MessageLoop::current()->RunAllPending();

[asargent_no_longer_on_chrome, 2011/03/09 18:13:01]

The code before was waiting for the file loop to run all pending tasks, but
you've changed it to MessageLoop::current(), which I think will return the UI
thread's MessageLoop. Doesn't this create a race condition such that where we
recreate the pref service below this block, the I/O on the file thread might not
be finished in time?

[Paweł Hajdan Jr., 2011/03/09 18:22:14]

There can be only one MessageLoop per thread. My interpretation of the previous
code is that file_loop was totally equivalent to MessageLoop::current() after
the declaration MessageLoop file_loop.

[asargent_no_longer_on_chrome, 2011/03/09 18:33:25]

But it was registering file_loop as the message loop for the file thread just
after creating it. Are you saying that doesn't work?

[Paweł Hajdan Jr., 2011/03/09 20:40:03]

After a more detailed look I think MessageLoop::current() was _correct_ but
potentially fragile. I've switched to waiting for an event signaled on FILE
thread. This will work both in case FILE thread is a "mock" thread running on
the same message loop, or a "real" thread with its own message loop.

Thank you for catching this, I think it is an important issue.

   }
 
   extension_pref_value_map_.reset(new ExtensionPrefValueMap);