base/message_pump_libevent.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_MESSAGE_PUMP_LIBEVENT_H_
   6 #define BASE_MESSAGE_PUMP_LIBEVENT_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/compiler_specific.h"
  10 #include "base/memory/weak_ptr.h"
  11 #include "base/message_pump.h"
  12 #include "base/observer_list.h"
  13 #include "base/threading/thread_checker.h"
  14 #include "base/time.h"
  15
  16 // Declare structs we need from libevent.h rather than including it
  17 struct event_base;
  18 struct event;
  19
  20 namespace base {
  21
  22 // Class to monitor sockets and issue callbacks when sockets are ready for I/O
  23 // TODO(dkegel): add support for background file IO somehow
  24 class BASE_EXPORT MessagePumpLibevent : public MessagePump {
  25  public:
  26   class IOObserver {
  27    public:
  28     IOObserver() {}
  29
  30     // An IOObserver is an object that receives IO notifications from the
  31     // MessagePump.
  32     //
  33     // NOTE: An IOObserver implementation should be extremely fast!
  34     virtual void WillProcessIOEvent() = 0;
  35     virtual void DidProcessIOEvent() = 0;
  36
  37    protected:
  38     virtual ~IOObserver() {}
  39   };
  40
  41   class FileDescriptorWatcher;
  42
  43   // Used with WatchFileDescriptor to asynchronously monitor the I/O readiness
  44   // of a file descriptor.
  45   class Watcher {
  46    public:
  47     // Called from MessageLoop::Run when an FD can be read from/written to
  48     // without blocking
  49     virtual void OnFileCanReadWithoutBlocking(int fd) = 0;
  50     virtual void OnFileCanWriteWithoutBlocking(int fd) = 0;
  51
  52    protected:
  53     virtual ~Watcher() {}
  54   };
  55
  56   // Object returned by WatchFileDescriptor to manage further watching.
  57   class FileDescriptorWatcher {
  58    public:
  59     FileDescriptorWatcher();
  60     ~FileDescriptorWatcher();  // Implicitly calls StopWatchingFileDescriptor.
  61
  62     // NOTE: These methods aren't called StartWatching()/StopWatching() to
  63     // avoid confusion with the win32 ObjectWatcher class.
  64
  65     // Stop watching the FD, always safe to call.  No-op if there's nothing
  66     // to do.
  67     bool StopWatchingFileDescriptor();
  68
  69    private:
  70     friend class MessagePumpLibevent;
  71     friend class MessagePumpLibeventTest;
  72
  73     // Called by MessagePumpLibevent, ownership of |e| is transferred to this
  74     // object.
  75     void Init(event* e);
  76
  77     // Used by MessagePumpLibevent to take ownership of event_.
  78     event* ReleaseEvent();
  79
  80     void set_pump(MessagePumpLibevent* pump) { pump_ = pump; }
  81     MessagePumpLibevent* pump() { return pump_; }
  82
  83     void set_watcher(Watcher* watcher) { watcher_ = watcher; }
  84
  85     void OnFileCanReadWithoutBlocking(int fd, MessagePumpLibevent* pump);
  86     void OnFileCanWriteWithoutBlocking(int fd, MessagePumpLibevent* pump);
  87
  88     event* event_;
  89     MessagePumpLibevent* pump_;
  90     Watcher* watcher_;
  91     base::WeakPtrFactory<FileDescriptorWatcher> weak_factory_;
  92
  93     DISALLOW_COPY_AND_ASSIGN(FileDescriptorWatcher);
  94   };
  95
  96   enum Mode {
  97     WATCH_READ = 1 << 0,
  98     WATCH_WRITE = 1 << 1,
  99     WATCH_READ_WRITE = WATCH_READ | WATCH_WRITE
 100   };
 101
 102   MessagePumpLibevent();
 103
 104   // Have the current thread's message loop watch for a a situation in which
 105   // reading/writing to the FD can be performed without blocking.
 106   // Callers must provide a preallocated FileDescriptorWatcher object which
 107   // can later be used to manage the lifetime of this event.
 108   // If a FileDescriptorWatcher is passed in which is already attached to
 109   // an event, then the effect is cumulative i.e. after the call |controller|
 110   // will watch both the previous event and the new one.
 111   // If an error occurs while calling this method in a cumulative fashion, the
 112   // event previously attached to |controller| is aborted.
 113   // Returns true on success.
 114   // Must be called on the same thread the message_pump is running on.
 115   // TODO(dkegel): switch to edge-triggered readiness notification
 116   bool WatchFileDescriptor(int fd,
 117                            bool persistent,
 118                            Mode mode,
 119                            FileDescriptorWatcher *controller,
 120                            Watcher *delegate);
 121
 122   void AddIOObserver(IOObserver* obs);
 123   void RemoveIOObserver(IOObserver* obs);
 124
 125   // MessagePump methods:
 126   virtual void Run(Delegate* delegate) OVERRIDE;
 127   virtual void Quit() OVERRIDE;
 128   virtual void ScheduleWork() OVERRIDE;
 129   virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time) OVERRIDE;
 130
 131  protected:
 132   virtual ~MessagePumpLibevent();
 133
 134  private:
 135   friend class MessagePumpLibeventTest;
 136
 137   void WillProcessIOEvent();
 138   void DidProcessIOEvent();
 139
 140   // Risky part of constructor.  Returns true on success.
 141   bool Init();
 142
 143   // Called by libevent to tell us a registered FD can be read/written to.
 144   static void OnLibeventNotification(int fd, short flags,
 145                                      void* context);
 146
 147   // Unix pipe used to implement ScheduleWork()
 148   // ... callback; called by libevent inside Run() when pipe is ready to read
 149   static void OnWakeup(int socket, short flags, void* context);
 150
 151   // This flag is set to false when Run should return.
 152   bool keep_running_;
 153
 154   // This flag is set when inside Run.
 155   bool in_run_;
 156
 157   // This flag is set if libevent has processed I/O events.
 158   bool processed_io_events_;
 159
 160   // The time at which we should call DoDelayedWork.
 161   TimeTicks delayed_work_time_;
 162
 163   // Libevent dispatcher.  Watches all sockets registered with it, and sends
 164   // readiness callbacks when a socket is ready for I/O.
 165   event_base* event_base_;
 166
 167   // ... write end; ScheduleWork() writes a single byte to it
 168   int wakeup_pipe_in_;
 169   // ... read end; OnWakeup reads it and then breaks Run() out of its sleep
 170   int wakeup_pipe_out_;
 171   // ... libevent wrapper for read end
 172   event* wakeup_event_;
 173
 174   ObserverList<IOObserver> io_observers_;
 175   ThreadChecker watch_file_descriptor_caller_checker_;
 176   DISALLOW_COPY_AND_ASSIGN(MessagePumpLibevent);
 177 };
 178
 179 }  // namespace base
 180
 181 #endif  // BASE_MESSAGE_PUMP_LIBEVENT_H_