Disallow UI/IO thread blocking on any other thread.

base/threading/thread_restrictions.h

 // Copyright (c) 2011 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.
 
 #ifndef BASE_THREADING_THREAD_RESTRICTIONS_H_
 #define BASE_THREADING_THREAD_RESTRICTIONS_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 
+class MetricsService;
+class RenderWidgetHelper;
+class TextInputClientMac;
+namespace chrome_browser_net {
+class Predictor;
+}
+namespace disk_cache {
+class BackendImpl;
+class InFlightIO;
+}
+
 namespace base {
 
+class Thread;
+
 // Certain behavior is disallowed on certain threads.  ThreadRestrictions helps
 // enforce these rules.  Examples of such rules:
 //
 // * Do not do blocking IO (makes the thread janky)
 // * Do not access Singleton/LazyInstance (may lead to shutdown crashes)
 //
 // Here's more about how the protection works:
 //
 // 1) If a thread should not be allowed to make IO calls, mark it:
 //      base::ThreadRestrictions::SetIOAllowed(false);
@@ skipping 53 matching lines @@
   // a discussion of where to add these checks.
   static void AssertIOAllowed();
 
   // Set whether the current thread can use singletons.  Returns the previous
   // value.
   static bool SetSingletonAllowed(bool allowed);
 
   // Check whether the current thread is allowed to use singletons (Singleton /
   // LazyInstance).  DCHECKs if not.
   static void AssertSingletonAllowed();
+
+  // Disable waiting on the current thread. Threads start out in the *allowed*
+  // state. Returns the previous value.
+  static void DisallowWaiting();
+
+  // Check whether the current thread is allowed to wait, and DCHECK if not.
+  static void AssertWaitAllowed();
 #else
   // In Release builds, inline the empty definitions of these functions so
   // that they can be compiled out.
   static bool SetIOAllowed(bool allowed) { return true; }
   static void AssertIOAllowed() {}
   static bool SetSingletonAllowed(bool allowed) { return true; }
   static void AssertSingletonAllowed() {}
+  static void DisallowWaiting() {}
+  static void AssertWaitAllowed() {}
 #endif
 
  private:
+  // DO NOT ADD ANY OTHER FRIEND STATEMENTS.
+  friend class ::RenderWidgetHelper;     // This is allowed, see documentation.
+  friend class Thread;                   // This is allowed.
+  friend class chrome_browser_net::Predictor;  // http://crbug.com/78451
+  friend class disk_cache::BackendImpl;  // http://crbug.com/74623
+  friend class disk_cache::InFlightIO;   // http://crbug.com/74623
+  friend class ::TextInputClientMac;     // http://crbug.com/121917
+  friend class ::MetricsService;         // http://crbug.com/124954
+
+#ifndef NDEBUG
+  static bool SetWaitAllowed(bool allowed);
+#else
+  static bool SetWaitAllowed(bool allowed) { return true; }
+#endif
+
+  // Constructing a ScopedAllowWait temporarily allows waiting on the current
+  // thread.  Doing this is almost always incorrect, which is why we limit who
+  // can use this through friend. If you find yourself needing to use this, find
+  // another way. Talk to jam or brettw.
+  class BASE_EXPORT ScopedAllowWait {
+   public:
+    ScopedAllowWait() { previous_value_ = SetWaitAllowed(true); }
+    ~ScopedAllowWait() { SetWaitAllowed(previous_value_); }
+   private:
+    // Whether singleton use is allowed when the ScopedAllowWait was
+    // constructed.
+    bool previous_value_;
+
+    DISALLOW_COPY_AND_ASSIGN(ScopedAllowWait);
+  };
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(ThreadRestrictions);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_RESTRICTIONS_H_