Consider PlatformThread::Join() to be blocking IO.

chrome/browser/browser_process_impl.cc

 // 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.
 
 #include "chrome/browser/browser_process_impl.h"
 
 #include <map>
 
 #include "app/clipboard/clipboard.h"
 #include "app/l10n_util.h"
 #include "base/command_line.h"
 #include "base/file_util.h"
 #include "base/path_service.h"
 #include "base/task.h"
 #include "base/thread.h"
+#include "base/thread_restrictions.h"
 #include "base/waitable_event.h"
 #include "chrome/browser/appcache/chrome_appcache_service.h"
 #include "chrome/browser/automation/automation_provider_list.h"
 #include "chrome/browser/browser_child_process_host.h"
 #include "chrome/browser/browser_list.h"
 #include "chrome/browser/browser_main.h"
 #include "chrome/browser/browser_process_sub_thread.h"
 #include "chrome/browser/browser_thread.h"
 #include "chrome/browser/browser_trial.h"
 #include "chrome/browser/debugger/debugger_wrapper.h"
@@ skipping 217 matching lines @@
   did_start_ = true;
   module_ref_count_++;
   return module_ref_count_;
 }
 
 unsigned int BrowserProcessImpl::ReleaseModule() {
   DCHECK(CalledOnValidThread());
   DCHECK_NE(0u, module_ref_count_);
   module_ref_count_--;
   if (0 == module_ref_count_) {
+    // Allow UI and IO threads to do blocking IO on shutdown, since we do a lot
+    // of it on shutdown for valid reasons.

[Evan Martin, 2010/12/10 21:43:04]

Heh, I hope this is the right place for this code...

[willchan no longer on Chromium, 2010/12/10 21:54:28]

What, you don't trust me? :)  Try it for yourself if you'd like.  But yeah, from
my extensive experience trawling through the morass of shutdown code nonsense,
this is the right place to do it.  It's interesting to note that APP_TERMINATING
is not the right signal to watch, because the automation provider can trigger
shutdown in ways that bypass APP_TERMINATING.  But this is the way we stop the
UI thread, so it's guaranteed to always work.

+    base::ThreadRestrictions::SetIOAllowed(true);
+    io_thread()->message_loop()->PostTask(
+        FROM_HERE,
+        NewRunnableFunction(&base::ThreadRestrictions::SetIOAllowed, true));
     MessageLoop::current()->PostTask(
         FROM_HERE, NewRunnableFunction(DidEndMainMessageLoop));
     MessageLoop::current()->Quit();
   }
   return module_ref_count_;
 }
 
 void BrowserProcessImpl::EndSession() {
 #if defined(OS_WIN) || defined(USE_X11)
   // Notify we are going away.
@@ skipping 553 matching lines @@
 }
 
 void BrowserProcessImpl::OnAutoupdateTimer() {
   if (CanAutorestartForUpdate()) {
     DLOG(WARNING) << "Detected update.  Restarting browser.";
     RestartPersistentInstance();
   }
 }
 
 #endif  // (defined(OS_WIN) || defined(OS_LINUX)) && !defined(OS_CHROMEOS)