base/threading/thread_restrictions.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_THREADING_THREAD_RESTRICTIONS_H_
   6 #define BASE_THREADING_THREAD_RESTRICTIONS_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/basictypes.h"
  10
  11 // See comment at top of thread_checker.h
  12 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
  13 #define ENABLE_THREAD_RESTRICTIONS 1
  14 #else
  15 #define ENABLE_THREAD_RESTRICTIONS 0
  16 #endif
  17
  18 class BrowserProcessImpl;
  19 class HistogramSynchronizer;
  20 class NativeBackendKWallet;
  21 class ScopedAllowWaitForLegacyWebViewApi;
  22
  23 namespace cc {
  24 class CompletionEvent;
  25 class TaskGraphRunner;
  26 }
  27 namespace chromeos {
  28 class BlockingMethodCaller;
  29 namespace system {
  30 class StatisticsProviderImpl;
  31 }
  32 }
  33 namespace chrome_browser_net {
  34 class Predictor;
  35 }
  36 namespace content {
  37 class BrowserGpuChannelHostFactory;
  38 class BrowserGpuMemoryBufferManager;
  39 class BrowserShutdownProfileDumper;
  40 class BrowserTestBase;
  41 class GpuChannelHost;
  42 class NestedMessagePumpAndroid;
  43 class RenderWidgetResizeHelper;
  44 class ScopedAllowWaitForAndroidLayoutTests;
  45 class TextInputClientMac;
  46 }  // namespace content
  47 namespace dbus {
  48 class Bus;
  49 }
  50 namespace disk_cache {
  51 class BackendImpl;
  52 class InFlightIO;
  53 }
  54 namespace mojo {
  55 namespace common {
  56 class WatcherThreadManager;
  57 }
  58 }
  59 namespace net {
  60 namespace internal {
  61 class AddressTrackerLinux;
  62 }
  63 }
  64
  65 namespace remoting {
  66 class AutoThread;
  67 }
  68
  69 namespace base {
  70
  71 namespace android {
  72 class JavaHandlerThread;
  73 }
  74
  75 class SequencedWorkerPool;
  76 class SimpleThread;
  77 class Thread;
  78 class ThreadTestHelper;
  79
  80 // Certain behavior is disallowed on certain threads.  ThreadRestrictions helps
  81 // enforce these rules.  Examples of such rules:
  82 //
  83 // * Do not do blocking IO (makes the thread janky)
  84 // * Do not access Singleton/LazyInstance (may lead to shutdown crashes)
  85 //
  86 // Here's more about how the protection works:
  87 //
  88 // 1) If a thread should not be allowed to make IO calls, mark it:
  89 //      base::ThreadRestrictions::SetIOAllowed(false);
  90 //    By default, threads *are* allowed to make IO calls.
  91 //    In Chrome browser code, IO calls should be proxied to the File thread.
  92 //
  93 // 2) If a function makes a call that will go out to disk, check whether the
  94 //    current thread is allowed:
  95 //      base::ThreadRestrictions::AssertIOAllowed();
  96 //
  97 //
  98 // Style tip: where should you put AssertIOAllowed checks?  It's best
  99 // if you put them as close to the disk access as possible, at the
 100 // lowest level.  This rule is simple to follow and helps catch all
 101 // callers.  For example, if your function GoDoSomeBlockingDiskCall()
 102 // only calls other functions in Chrome and not fopen(), you should go
 103 // add the AssertIOAllowed checks in the helper functions.
 104
 105 class BASE_EXPORT ThreadRestrictions {
 106  public:
 107   // Constructing a ScopedAllowIO temporarily allows IO for the current
 108   // thread.  Doing this is almost certainly always incorrect.
 109   class BASE_EXPORT ScopedAllowIO {
 110    public:
 111     ScopedAllowIO() { previous_value_ = SetIOAllowed(true); }
 112     ~ScopedAllowIO() { SetIOAllowed(previous_value_); }
 113    private:
 114     // Whether IO is allowed when the ScopedAllowIO was constructed.
 115     bool previous_value_;
 116
 117     DISALLOW_COPY_AND_ASSIGN(ScopedAllowIO);
 118   };
 119
 120   // Constructing a ScopedAllowSingleton temporarily allows accessing for the
 121   // current thread.  Doing this is almost always incorrect.
 122   class BASE_EXPORT ScopedAllowSingleton {
 123    public:
 124     ScopedAllowSingleton() { previous_value_ = SetSingletonAllowed(true); }
 125     ~ScopedAllowSingleton() { SetSingletonAllowed(previous_value_); }
 126    private:
 127     // Whether singleton use is allowed when the ScopedAllowSingleton was
 128     // constructed.
 129     bool previous_value_;
 130
 131     DISALLOW_COPY_AND_ASSIGN(ScopedAllowSingleton);
 132   };
 133
 134 #if ENABLE_THREAD_RESTRICTIONS
 135   // Set whether the current thread to make IO calls.
 136   // Threads start out in the *allowed* state.
 137   // Returns the previous value.
 138   static bool SetIOAllowed(bool allowed);
 139
 140   // Check whether the current thread is allowed to make IO calls,
 141   // and DCHECK if not.  See the block comment above the class for
 142   // a discussion of where to add these checks.
 143   static void AssertIOAllowed();
 144
 145   // Set whether the current thread can use singletons.  Returns the previous
 146   // value.
 147   static bool SetSingletonAllowed(bool allowed);
 148
 149   // Check whether the current thread is allowed to use singletons (Singleton /
 150   // LazyInstance).  DCHECKs if not.
 151   static void AssertSingletonAllowed();
 152
 153   // Disable waiting on the current thread. Threads start out in the *allowed*
 154   // state. Returns the previous value.
 155   static void DisallowWaiting();
 156
 157   // Check whether the current thread is allowed to wait, and DCHECK if not.
 158   static void AssertWaitAllowed();
 159 #else
 160   // Inline the empty definitions of these functions so that they can be
 161   // compiled out.
 162   static bool SetIOAllowed(bool allowed) { return true; }
 163   static void AssertIOAllowed() {}
 164   static bool SetSingletonAllowed(bool allowed) { return true; }
 165   static void AssertSingletonAllowed() {}
 166   static void DisallowWaiting() {}
 167   static void AssertWaitAllowed() {}
 168 #endif
 169
 170  private:
 171   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to jam or brettw first.
 172   // BEGIN ALLOWED USAGE.
 173   friend class content::BrowserShutdownProfileDumper;
 174   friend class content::BrowserTestBase;
 175   friend class content::NestedMessagePumpAndroid;
 176   friend class content::RenderWidgetResizeHelper;
 177   friend class content::ScopedAllowWaitForAndroidLayoutTests;
 178   friend class ::HistogramSynchronizer;
 179   friend class ::ScopedAllowWaitForLegacyWebViewApi;
 180   friend class cc::CompletionEvent;
 181   friend class cc::TaskGraphRunner;
 182   friend class mojo::common::WatcherThreadManager;
 183   friend class remoting::AutoThread;
 184   friend class MessagePumpDefault;
 185   friend class SequencedWorkerPool;
 186   friend class SimpleThread;
 187   friend class Thread;
 188   friend class ThreadTestHelper;
 189   friend class PlatformThread;
 190   friend class android::JavaHandlerThread;
 191
 192   // END ALLOWED USAGE.
 193   // BEGIN USAGE THAT NEEDS TO BE FIXED.
 194   friend class ::chromeos::BlockingMethodCaller;  // http://crbug.com/125360
 195   friend class ::chromeos::system::StatisticsProviderImpl;  // http://crbug.com/125385
 196   friend class chrome_browser_net::Predictor;     // http://crbug.com/78451
 197   friend class
 198       content::BrowserGpuChannelHostFactory;      // http://crbug.com/125248
 199   friend class
 200       content::BrowserGpuMemoryBufferManager;     // http://crbug.com/420368
 201   friend class content::GpuChannelHost;           // http://crbug.com/125264
 202   friend class content::TextInputClientMac;       // http://crbug.com/121917
 203   friend class dbus::Bus;                         // http://crbug.com/125222
 204   friend class disk_cache::BackendImpl;           // http://crbug.com/74623
 205   friend class disk_cache::InFlightIO;            // http://crbug.com/74623
 206   friend class net::internal::AddressTrackerLinux;  // http://crbug.com/125097
 207   friend class ::BrowserProcessImpl;              // http://crbug.com/125207
 208   friend class ::NativeBackendKWallet;            // http://crbug.com/125331
 209   // END USAGE THAT NEEDS TO BE FIXED.
 210
 211 #if ENABLE_THREAD_RESTRICTIONS
 212   static bool SetWaitAllowed(bool allowed);
 213 #else
 214   static bool SetWaitAllowed(bool allowed) { return true; }
 215 #endif
 216
 217   // Constructing a ScopedAllowWait temporarily allows waiting on the current
 218   // thread.  Doing this is almost always incorrect, which is why we limit who
 219   // can use this through friend. If you find yourself needing to use this, find
 220   // another way. Talk to jam or brettw.
 221   class BASE_EXPORT ScopedAllowWait {
 222    public:
 223     ScopedAllowWait() { previous_value_ = SetWaitAllowed(true); }
 224     ~ScopedAllowWait() { SetWaitAllowed(previous_value_); }
 225    private:
 226     // Whether singleton use is allowed when the ScopedAllowWait was
 227     // constructed.
 228     bool previous_value_;
 229
 230     DISALLOW_COPY_AND_ASSIGN(ScopedAllowWait);
 231   };
 232
 233   DISALLOW_IMPLICIT_CONSTRUCTORS(ThreadRestrictions);
 234 };
 235
 236 }  // namespace base
 237
 238 #endif  // BASE_THREADING_THREAD_RESTRICTIONS_H_