base/message_pump_libevent.h

   1 // Copyright (c) 2011 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 #pragma once
   8
   9 #include "base/basictypes.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_API 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     virtual ~Watcher() {}
  48     // Called from MessageLoop::Run when an FD can be read from/written to
  49     // without blocking
  50     virtual void OnFileCanReadWithoutBlocking(int fd) = 0;
  51     virtual void OnFileCanWriteWithoutBlocking(int fd) = 0;
  52   };
  53
  54   // Object returned by WatchFileDescriptor to manage further watching.
  55   class FileDescriptorWatcher {
  56    public:
  57     FileDescriptorWatcher();
  58     ~FileDescriptorWatcher();  // Implicitly calls StopWatchingFileDescriptor.
  59
  60     // NOTE: These methods aren't called StartWatching()/StopWatching() to
  61     // avoid confusion with the win32 ObjectWatcher class.
  62
  63     // Stop watching the FD, always safe to call.  No-op if there's nothing
  64     // to do.
  65     bool StopWatchingFileDescriptor();
  66
  67    private:
  68     friend class MessagePumpLibevent;
  69     friend class MessagePumpLibeventTest;
  70
  71     // Called by MessagePumpLibevent, ownership of |e| is transferred to this
  72     // object.
  73     void Init(event* e, bool is_persistent);
  74
  75     // Used by MessagePumpLibevent to take ownership of event_.
  76     event *ReleaseEvent();
  77
  78     void set_pump(MessagePumpLibevent* pump) { pump_ = pump; }
  79     MessagePumpLibevent* pump() { return pump_; }
  80
  81     void set_watcher(Watcher* watcher) { watcher_ = watcher; }
  82
  83     void OnFileCanReadWithoutBlocking(int fd, MessagePumpLibevent* pump);
  84     void OnFileCanWriteWithoutBlocking(int fd, MessagePumpLibevent* pump);
  85
  86     bool is_persistent_;  // false if this event is one-shot.
  87     event* event_;
  88     MessagePumpLibevent* pump_;
  89     Watcher* watcher_;
  90     base::WeakPtrFactory<FileDescriptorWatcher> weak_factory_;
  91
  92     DISALLOW_COPY_AND_ASSIGN(FileDescriptorWatcher);
  93   };
  94
  95   enum Mode {
  96     WATCH_READ = 1 << 0,
  97     WATCH_WRITE = 1 << 1,
  98     WATCH_READ_WRITE = WATCH_READ | WATCH_WRITE
  99   };
 100
 101   MessagePumpLibevent();
 102   virtual ~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);
 127   virtual void Quit();
 128   virtual void ScheduleWork();
 129   virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time);
 130
 131  private:
 132   friend class MessagePumpLibeventTest;
 133
 134   void WillProcessIOEvent();
 135   void DidProcessIOEvent();
 136
 137   // Risky part of constructor.  Returns true on success.
 138   bool Init();
 139
 140   // Called by libevent to tell us a registered FD can be read/written to.
 141   static void OnLibeventNotification(int fd, short flags,
 142                                      void* context);
 143
 144   // Unix pipe used to implement ScheduleWork()
 145   // ... callback; called by libevent inside Run() when pipe is ready to read
 146   static void OnWakeup(int socket, short flags, void* context);
 147
 148   // This flag is set to false when Run should return.
 149   bool keep_running_;
 150
 151   // This flag is set when inside Run.
 152   bool in_run_;
 153
 154   // This flag is set if libevent has processed I/O events.
 155   bool processed_io_events_;
 156
 157   // The time at which we should call DoDelayedWork.
 158   TimeTicks delayed_work_time_;
 159
 160   // Libevent dispatcher.  Watches all sockets registered with it, and sends
 161   // readiness callbacks when a socket is ready for I/O.
 162   event_base* event_base_;
 163
 164   // ... write end; ScheduleWork() writes a single byte to it
 165   int wakeup_pipe_in_;
 166   // ... read end; OnWakeup reads it and then breaks Run() out of its sleep
 167   int wakeup_pipe_out_;
 168   // ... libevent wrapper for read end
 169   event* wakeup_event_;
 170
 171   ObserverList<IOObserver> io_observers_;
 172   ThreadChecker watch_file_descriptor_caller_checker_;
 173   DISALLOW_COPY_AND_ASSIGN(MessagePumpLibevent);
 174 };
 175
 176 }  // namespace base
 177
 178 #endif  // BASE_MESSAGE_PUMP_LIBEVENT_H_