Home | History | Annotate | Download | only in message_loop 
      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   virtual ~MessagePumpLibevent();
    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   virtual void Run(Delegate* delegate) OVERRIDE;
    126   virtual void Quit() OVERRIDE;
    127   virtual void ScheduleWork() OVERRIDE;
    128   virtual 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_
    178