Disallow UI/IO thread blocking on any other thread.

chrome/browser/net/predictor.cc

 // Copyright (c) 2012 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/net/predictor.h"
 
 #include <algorithm>
 #include <cmath>
 #include <set>
 #include <sstream>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/string_split.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/time.h"
 #include "base/values.h"
 #include "chrome/browser/io_thread.h"
 #include "chrome/browser/net/preconnect.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/prefs/session_startup_pref.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 730 matching lines @@
         base::Bind(
             &SaveDnsPrefetchStateForNextStartupAndTrimOnIOThread,
             update_startup_list.Get(),
             update_referral_list.Get(),
             &completion,
             this));
 
     // TODO(jar): Synchronous waiting for the IO thread is a potential source
     // to deadlocks and should be investigated. See http://crbug.com/78451.
     DCHECK(posted);
-    if (posted)
+    if (posted) {
+      // http://crbug.com/124954
+      base::ThreadRestrictions::ScopedAllowWait allow_wait;
       completion.Wait();
+    }
   }
 }
 
 void Predictor::SaveDnsPrefetchStateForNextStartupAndTrim(
     base::ListValue* startup_list,
     base::ListValue* referral_list,
     base::WaitableEvent* completion) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   if (initial_observer_.get())
     initial_observer_->GetInitialDnsResolutionList(startup_list);
@@ skipping 389 matching lines @@
     IOThread* io_thread,
     net::URLRequestContextGetter* getter) {
   // Empty function for unittests.
 }
 
 void SimplePredictor::ShutdownOnUIThread(PrefService* user_prefs) {
   SetShutdown(true);
 }
 
 }  // namespace chrome_browser_net