base/message_loop/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_LOOP_MESSAGE_PUMP_LIBEVENT_H_
   6 #define BASE_MESSAGE_LOOP_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_loop/message_pump.h"
  12 #include "base/observer_list.h"
  13 #include "base/threading/thread_checker.h"
  14 #include "base/time/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   // Used with WatchFileDescriptor to asynchronously monitor the I/O readiness
  42   // of a file descriptor.
  43   class Watcher {
  44    public:
  45     // Called from MessageLoop::Run when an FD can be read from/written to
  46     // without blocking
  47     virtual void OnFileCanReadWithoutBlocking(int fd) = 0;
  48     virtual void OnFileCanWriteWithoutBlocking(int fd) = 0;
  49
  50    protected:
  51     virtual ~Watcher() {}
  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);
  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() const { 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     event* event_;
  87     MessagePumpLibevent* pump_;
  88     Watcher* watcher_;
  89     WeakPtrFactory<FileDescriptorWatcher> weak_factory_;
  90
  91     DISALLOW_COPY_AND_ASSIGN(FileDescriptorWatcher);
  92   };
  93
  94   enum Mode {
  95     WATCH_READ = 1 << 0,
  96     WATCH_WRITE = 1 << 1,
  97     WATCH_READ_WRITE = WATCH_READ | WATCH_WRITE
  98   };
  99
 100   MessagePumpLibevent();
 101   ~MessagePumpLibevent() override;
 102
 103   // Have the current thread's message loop watch for a a situation in which
 104   // reading/writing to the FD can be performed without blocking.
 105   // Callers must provide a preallocated FileDescriptorWatcher object which
 106   // can later be used to manage the lifetime of this event.
 107   // If a FileDescriptorWatcher is passed in which is already attached to
 108   // an event, then the effect is cumulative i.e. after the call |controller|
 109   // will watch both the previous event and the new one.
 110   // If an error occurs while calling this method in a cumulative fashion, the
 111   // event previously attached to |controller| is aborted.
 112   // Returns true on success.
 113   // Must be called on the same thread the message_pump is running on.
 114   // TODO(dkegel): switch to edge-triggered readiness notification
 115   bool WatchFileDescriptor(int fd,
 116                            bool persistent,
 117                            int mode,
 118                            FileDescriptorWatcher *controller,
 119                            Watcher *delegate);
 120
 121   void AddIOObserver(IOObserver* obs);
 122   void RemoveIOObserver(IOObserver* obs);
 123
 124   // MessagePump methods:
 125   void Run(Delegate* delegate) override;
 126   void Quit() override;
 127   void ScheduleWork() override;
 128   void ScheduleDelayedWork(const TimeTicks& delayed_work_time) override;
 129
 130  private:
 131   friend class MessagePumpLibeventTest;
 132
 133   void WillProcessIOEvent();
 134   void DidProcessIOEvent();
 135
 136   // Risky part of constructor.  Returns true on success.
 137   bool Init();
 138
 139   // Called by libevent to tell us a registered FD can be read/written to.
 140   static void OnLibeventNotification(int fd, short flags,
 141                                      void* context);
 142
 143   // Unix pipe used to implement ScheduleWork()
 144   // ... callback; called by libevent inside Run() when pipe is ready to read
 145   static void OnWakeup(int socket, short flags, void* context);
 146
 147   // This flag is set to false when Run should return.
 148   bool keep_running_;
 149
 150   // This flag is set when inside Run.
 151   bool in_run_;
 152
 153   // This flag is set if libevent has processed I/O events.
 154   bool processed_io_events_;
 155
 156   // The time at which we should call DoDelayedWork.
 157   TimeTicks delayed_work_time_;
 158
 159   // Libevent dispatcher.  Watches all sockets registered with it, and sends
 160   // readiness callbacks when a socket is ready for I/O.
 161   event_base* event_base_;
 162
 163   // ... write end; ScheduleWork() writes a single byte to it
 164   int wakeup_pipe_in_;
 165   // ... read end; OnWakeup reads it and then breaks Run() out of its sleep
 166   int wakeup_pipe_out_;
 167   // ... libevent wrapper for read end
 168   event* wakeup_event_;
 169
 170   ObserverList<IOObserver> io_observers_;
 171   ThreadChecker watch_file_descriptor_caller_checker_;
 172   DISALLOW_COPY_AND_ASSIGN(MessagePumpLibevent);
 173 };
 174
 175 }  // namespace base
 176
 177 #endif  // BASE_MESSAGE_LOOP_MESSAGE_PUMP_LIBEVENT_H_