base/run_loop.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_RUN_LOOP_H_
   6 #define BASE_RUN_LOOP_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/callback.h"
  10 #include "base/memory/weak_ptr.h"
  11 #include "base/message_loop/message_loop.h"
  12
  13 namespace base {
  14 #if defined(OS_ANDROID)
  15 class MessagePumpForUI;
  16 #endif
  17
  18 #if defined(OS_WIN)
  19 class MessagePumpDispatcher;
  20 #endif
  21
  22 #if defined(OS_IOS)
  23 class MessagePumpUIApplication;
  24 #endif
  25
  26 // Helper class to Run a nested MessageLoop. Please do not use nested
  27 // MessageLoops in production code! If you must, use this class instead of
  28 // calling MessageLoop::Run/Quit directly. RunLoop::Run can only be called once
  29 // per RunLoop lifetime. Create a RunLoop on the stack and call Run/Quit to run
  30 // a nested MessageLoop.
  31 class BASE_EXPORT RunLoop {
  32  public:
  33   RunLoop();
  34 #if defined(OS_WIN)
  35   explicit RunLoop(MessagePumpDispatcher* dispatcher);
  36 #endif
  37   ~RunLoop();
  38
  39   // Run the current MessageLoop. This blocks until Quit is called. Before
  40   // calling Run, be sure to grab an AsWeakPtr or the QuitClosure in order to
  41   // stop the MessageLoop asynchronously. MessageLoop::Quit and QuitNow will
  42   // also trigger a return from Run, but those are deprecated.
  43   void Run();
  44
  45   // Run the current MessageLoop until it doesn't find any tasks or messages in
  46   // the queue (it goes idle). WARNING: This may never return! Only use this
  47   // when repeating tasks such as animated web pages have been shut down.
  48   void RunUntilIdle();
  49
  50   bool running() const { return running_; }
  51
  52   // Quit an earlier call to Run(). There can be other nested RunLoops servicing
  53   // the same task queue (MessageLoop); Quitting one RunLoop has no bearing on
  54   // the others. Quit can be called before, during or after Run. If called
  55   // before Run, Run will return immediately when called. Calling Quit after the
  56   // RunLoop has already finished running has no effect.
  57   //
  58   // WARNING: You must NEVER assume that a call to Quit will terminate the
  59   // targetted message loop. If a nested message loop continues running, the
  60   // target may NEVER terminate. It is very easy to livelock (run forever) in
  61   // such a case.
  62   void Quit();
  63
  64   // Convenience method to get a closure that safely calls Quit (has no effect
  65   // if the RunLoop instance is gone).
  66   //
  67   // Example:
  68   //   RunLoop run_loop;
  69   //   PostTask(run_loop.QuitClosure());
  70   //   run_loop.Run();
  71   base::Closure QuitClosure();
  72
  73  private:
  74   friend class MessageLoop;
  75 #if defined(OS_ANDROID)
  76   // Android doesn't support the blocking MessageLoop::Run, so it calls
  77   // BeforeRun and AfterRun directly.
  78   friend class base::MessagePumpForUI;
  79 #endif
  80
  81 #if defined(OS_IOS)
  82   // iOS doesn't support the blocking MessageLoop::Run, so it calls
  83   // BeforeRun directly.
  84   friend class base::MessagePumpUIApplication;
  85 #endif
  86
  87   // Return false to abort the Run.
  88   bool BeforeRun();
  89   void AfterRun();
  90
  91   MessageLoop* loop_;
  92
  93   // Parent RunLoop or NULL if this is the top-most RunLoop.
  94   RunLoop* previous_run_loop_;
  95
  96 #if defined(OS_WIN)
  97   MessagePumpDispatcher* dispatcher_;
  98 #endif
  99
 100   // Used to count how many nested Run() invocations are on the stack.
 101   int run_depth_;
 102
 103   bool run_called_;
 104   bool quit_called_;
 105   bool running_;
 106
 107   // Used to record that QuitWhenIdle() was called on the MessageLoop, meaning
 108   // that we should quit Run once it becomes idle.
 109   bool quit_when_idle_received_;
 110
 111   // WeakPtrFactory for QuitClosure safety.
 112   base::WeakPtrFactory<RunLoop> weak_factory_;
 113
 114   DISALLOW_COPY_AND_ASSIGN(RunLoop);
 115 };
 116
 117 }  // namespace base
 118
 119 #endif  // BASE_RUN_LOOP_H_