message_pump_libevent.h revision 3f50c38dc070f4bb515c1b64450dae14f316474e 
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/message_pump.h"
11#include "base/observer_list.h"
12#include "base/time.h"
13
14// Declare structs we need from libevent.h rather than including it
15struct event_base;
16struct event;
17
18namespace base {
19
20// Class to monitor sockets and issue callbacks when sockets are ready for I/O
21// TODO(dkegel): add support for background file IO somehow
22class MessagePumpLibevent : public MessagePump {
23 public:
24  class IOObserver {
25   public:
26    IOObserver() {}
27
28    // An IOObserver is an object that receives IO notifications from the
29    // MessagePump.
30    //
31    // NOTE: An IOObserver implementation should be extremely fast!
32    virtual void WillProcessIOEvent() = 0;
33    virtual void DidProcessIOEvent() = 0;
34
35   protected:
36    virtual ~IOObserver() {}
37  };
38
39  // Used with WatchFileDescptor to asynchronously monitor the I/O readiness of
40  // a File Descriptor.
41  class Watcher {
42   public:
43    virtual ~Watcher() {}
44    // Called from MessageLoop::Run when an FD can be read from/written to
45    // without blocking
46    virtual void OnFileCanReadWithoutBlocking(int fd) = 0;
47    virtual void OnFileCanWriteWithoutBlocking(int fd) = 0;
48  };
49
50  // Object returned by WatchFileDescriptor to manage further watching.
51  class FileDescriptorWatcher {
52   public:
53    FileDescriptorWatcher();
54    ~FileDescriptorWatcher();  // Implicitly calls StopWatchingFileDescriptor.
55
56    // NOTE: These methods aren't called StartWatching()/StopWatching() to
57    // avoid confusion with the win32 ObjectWatcher class.
58
59    // Stop watching the FD, always safe to call.  No-op if there's nothing
60    // to do.
61    bool StopWatchingFileDescriptor();
62
63   private:
64    friend class MessagePumpLibevent;
65
66    // Called by MessagePumpLibevent, ownership of |e| is transferred to this
67    // object.
68    void Init(event* e, bool is_persistent);
69
70    // Used by MessagePumpLibevent to take ownership of event_.
71    event *ReleaseEvent();
72
73    void set_pump(MessagePumpLibevent* pump) { pump_ = pump; }
74    MessagePumpLibevent* pump() { return pump_; }
75
76    void set_watcher(Watcher* watcher) { watcher_ = watcher; }
77
78    void OnFileCanReadWithoutBlocking(int fd, MessagePumpLibevent* pump);
79    void OnFileCanWriteWithoutBlocking(int fd, MessagePumpLibevent* pump);
80
81    bool is_persistent_;  // false if this event is one-shot.
82    event* event_;
83    MessagePumpLibevent* pump_;
84    Watcher* watcher_;
85
86    DISALLOW_COPY_AND_ASSIGN(FileDescriptorWatcher);
87  };
88
89  enum Mode {
90    WATCH_READ = 1 << 0,
91    WATCH_WRITE = 1 << 1,
92    WATCH_READ_WRITE = WATCH_READ | WATCH_WRITE
93  };
94
95  MessagePumpLibevent();
96  virtual ~MessagePumpLibevent();
97
98  // Have the current thread's message loop watch for a a situation in which
99  // reading/writing to the FD can be performed without blocking.
100  // Callers must provide a preallocated FileDescriptorWatcher object which
101  // can later be used to manage the lifetime of this event.
102  // If a FileDescriptorWatcher is passed in which is already attached to
103  // an event, then the effect is cumulative i.e. after the call |controller|
104  // will watch both the previous event and the new one.
105  // If an error occurs while calling this method in a cumulative fashion, the
106  // event previously attached to |controller| is aborted.
107  // Returns true on success.
108  // TODO(dkegel): switch to edge-triggered readiness notification
109  bool WatchFileDescriptor(int fd,
110                           bool persistent,
111                           Mode mode,
112                           FileDescriptorWatcher *controller,
113                           Watcher *delegate);
114
115  void AddIOObserver(IOObserver* obs);
116  void RemoveIOObserver(IOObserver* obs);
117
118  // MessagePump methods:
119  virtual void Run(Delegate* delegate);
120  virtual void Quit();
121  virtual void ScheduleWork();
122  virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time);
123
124 private:
125  void WillProcessIOEvent();
126  void DidProcessIOEvent();
127
128  // Risky part of constructor.  Returns true on success.
129  bool Init();
130
131  // Called by libevent to tell us a registered FD can be read/written to.
132  static void OnLibeventNotification(int fd, short flags,
133                                     void* context);
134
135  // Unix pipe used to implement ScheduleWork()
136  // ... callback; called by libevent inside Run() when pipe is ready to read
137  static void OnWakeup(int socket, short flags, void* context);
138
139  // This flag is set to false when Run should return.
140  bool keep_running_;
141
142  // This flag is set when inside Run.
143  bool in_run_;
144
145  // The time at which we should call DoDelayedWork.
146  TimeTicks delayed_work_time_;
147
148  // Libevent dispatcher.  Watches all sockets registered with it, and sends
149  // readiness callbacks when a socket is ready for I/O.
150  event_base* event_base_;
151
152  // ... write end; ScheduleWork() writes a single byte to it
153  int wakeup_pipe_in_;
154  // ... read end; OnWakeup reads it and then breaks Run() out of its sleep
155  int wakeup_pipe_out_;
156  // ... libevent wrapper for read end
157  event* wakeup_event_;
158
159  ObserverList<IOObserver> io_observers_;
160
161  DISALLOW_COPY_AND_ASSIGN(MessagePumpLibevent);
162};
163
164}  // namespace base
165
166#endif  // BASE_MESSAGE_PUMP_LIBEVENT_H_
167