base/threading/thread_restrictions.h

// 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.

#ifndef BASE_THREADING_THREAD_RESTRICTIONS_H_
#define BASE_THREADING_THREAD_RESTRICTIONS_H_

#include "base/base_export.h"
#include "base/basictypes.h"

// See comment at top of thread_checker.h
#if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
#define ENABLE_THREAD_RESTRICTIONS 1
#else
#define ENABLE_THREAD_RESTRICTIONS 0
#endif

class AcceleratedPresenter;
class BrowserProcessImpl;
class HistogramSynchronizer;
class MetricsService;
class NativeBackendKWallet;
class ScopedAllowWaitForLegacyWebViewApi;
class TestingAutomationProvider;

namespace browser_sync {
class NonFrontendDataTypeController;
class UIModelWorker;
}
namespace cc {
class CompletionEvent;
}
namespace chromeos {
class AudioMixerAlsa;
class BlockingMethodCaller;
namespace system {
class StatisticsProviderImpl;
}
}
namespace chrome_browser_net {
class Predictor;
}
namespace content {
class BrowserGpuChannelHostFactory;
class GLHelper;
class GpuChannelHost;
class RenderWidgetHelper;
class TextInputClientMac;
}
namespace dbus {
class Bus;
}
namespace disk_cache {
class BackendImpl;
class InFlightIO;
}
namespace media {
class AudioOutputController;
}
namespace net {
class FileStreamPosix;
class FileStreamWin;
class NetworkManagerApi;
}

namespace remoting {
class AutoThread;
}

namespace base {

class SequencedWorkerPool;
class SimpleThread;
class Thread;
class ThreadTestHelper;

// 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);
//    By default, threads *are* allowed to make IO calls.
//    In Chrome browser code, IO calls should be proxied to the File thread.
//
// 2) If a function makes a call that will go out to disk, check whether the
//    current thread is allowed:
//      base::ThreadRestrictions::AssertIOAllowed();
//
//
// Style tip: where should you put AssertIOAllowed checks?  It's best
// if you put them as close to the disk access as possible, at the
// lowest level.  This rule is simple to follow and helps catch all
// callers.  For example, if your function GoDoSomeBlockingDiskCall()
// only calls other functions in Chrome and not fopen(), you should go
// add the AssertIOAllowed checks in the helper functions.

class BASE_EXPORT ThreadRestrictions {
 public:
  // Constructing a ScopedAllowIO temporarily allows IO for the current
  // thread.  Doing this is almost certainly always incorrect.
  class BASE_EXPORT ScopedAllowIO {
   public:
    ScopedAllowIO() { previous_value_ = SetIOAllowed(true); }
    ~ScopedAllowIO() { SetIOAllowed(previous_value_); }
   private:
    // Whether IO is allowed when the ScopedAllowIO was constructed.
    bool previous_value_;

    DISALLOW_COPY_AND_ASSIGN(ScopedAllowIO);
  };

  // Constructing a ScopedAllowSingleton temporarily allows accessing for the
  // current thread.  Doing this is almost always incorrect.
  class BASE_EXPORT ScopedAllowSingleton {
   public:
    ScopedAllowSingleton() { previous_value_ = SetSingletonAllowed(true); }
    ~ScopedAllowSingleton() { SetSingletonAllowed(previous_value_); }
   private:
    // Whether singleton use is allowed when the ScopedAllowSingleton was
    // constructed.
    bool previous_value_;

    DISALLOW_COPY_AND_ASSIGN(ScopedAllowSingleton);
  };

#if ENABLE_THREAD_RESTRICTIONS
  // Set whether the current thread to make IO calls.
  // Threads start out in the *allowed* state.
  // Returns the previous value.
  static bool SetIOAllowed(bool allowed);

  // Check whether the current thread is allowed to make IO calls,
  // and DCHECK if not.  See the block comment above the class for
  // 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
  // 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, talk to jam or brettw first.
  // BEGIN ALLOWED USAGE.
  friend class content::RenderWidgetHelper;
  friend class ::HistogramSynchronizer;
  friend class ::ScopedAllowWaitForLegacyWebViewApi;
  friend class ::TestingAutomationProvider;
  friend class cc::CompletionEvent;
  friend class remoting::AutoThread;
  friend class SequencedWorkerPool;
  friend class SimpleThread;
  friend class Thread;
  friend class ThreadTestHelper;

  // END ALLOWED USAGE.
  // BEGIN USAGE THAT NEEDS TO BE FIXED.
  friend class ::chromeos::AudioMixerAlsa;        // http://crbug.com/125206
  friend class ::chromeos::BlockingMethodCaller;  // http://crbug.com/125360
  friend class ::chromeos::system::StatisticsProviderImpl;  // http://crbug.com/125385
  friend class browser_sync::NonFrontendDataTypeController;  // http://crbug.com/19757
  friend class browser_sync::UIModelWorker;       // http://crbug.com/19757
  friend class chrome_browser_net::Predictor;     // http://crbug.com/78451
  friend class
      content::BrowserGpuChannelHostFactory;      // http://crbug.com/125248
  friend class content::GLHelper;                 // http://crbug.com/125415
  friend class content::GpuChannelHost;           // http://crbug.com/125264
  friend class content::TextInputClientMac;       // http://crbug.com/121917
  friend class dbus::Bus;                         // http://crbug.com/125222
  friend class disk_cache::BackendImpl;           // http://crbug.com/74623
  friend class disk_cache::InFlightIO;            // http://crbug.com/74623
  friend class media::AudioOutputController;      // http://crbug.com/120973
  friend class net::FileStreamPosix;              // http://crbug.com/115067
  friend class net::FileStreamWin;                // http://crbug.com/115067
  friend class net::NetworkManagerApi;            // http://crbug.com/125097
  friend class ::AcceleratedPresenter;            // http://crbug.com/125391
  friend class ::BrowserProcessImpl;              // http://crbug.com/125207
  friend class ::MetricsService;                  // http://crbug.com/124954
  friend class ::NativeBackendKWallet;            // http://crbug.com/125331
  // END USAGE THAT NEEDS TO BE FIXED.

#if ENABLE_THREAD_RESTRICTIONS
  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_