Add initial sketch to shill repository

shill_event.h

+// Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SHILL_EVENT_
+#define SHILL_EVENT_
+
+#include <vector>
+
+namespace shill {
+
+// This is a pure-virtual base class for callback objects which can be
+// queued up and called later.  The callback virtual method takes a single
+// argument, which will be handed to the dispatcher to call on all listeners.
+template <typename Arg>
+class Callback {

[Chris Masone, 2011/03/10 18:44:15]

I won't push too hard, but Chrome does have a notion of event loops and tasks
you can schedule/post to them.  The Chrome main message loop == the glib main
loop, even.  It gets a little awkward if you want to use both the chrome and
glib mechanisms for doing event handling, but it can be done.  If you're really
just doing task posting and handling dbus, it works pretty good.  If it doesn't
do stuff you need, though, don't worry about it.

[Sam Leffler, 2011/03/11 01:30:42]

I haven't looked at chrome's event + task support but I'd echo this comment--the
more existing code you can re-use the easier it should be to get people ramped
up on shill.

+ public:
+  virtual ~Callback() {}
+  virtual void Run(Arg arg) = 0;
+};
+
+// This is a callback subclass that contains an object and method to call.
+// These methods take a passed-in argument specific to the callback type.
+template <typename Class, typename Arg>
+class ClassCallback : public Callback<Arg> {
+ public:
+  typedef void (Class::*MethodType)(Arg arg);
+
+  ClassCallback(Class* object, MethodType method)
+    : object_(object), method_(method) {}
+  ~ClassCallback() {}
+
+  void Run(Arg arg) {
+    (object_->*method_)(arg);
+  }
+
+ private:
+  Class* object_;
+  MethodType method_;
+};
+
+// This is the event queue superclass, which contains a function for
+// dispatching all events in the queue to their respective listeners.
+// A common "AlertDispatcher()" function is used by subclasses to alert
+// the central dispatcher that events have been queued and a dispatch
+// should be performed soon.
+class EventDispatcher;
+class EventQueueItem {
+ public:
+  EventQueueItem(EventDispatcher *dispatcher);
+  ~EventQueueItem();
+  virtual void Dispatch() = 0;
+  void AlertDispatcher();
+ private:
+  EventDispatcher *dispatcher_;
+};
+
+// This is a template subclass of EventQueueItem which is specific to
+// a particular argument type.  This object contains a queue of events
+// waiting for delivery to liesteners, and a list of even callbacks --
+// the listeners for this event.
+template <typename Arg>
+class EventQueue : public EventQueueItem {
+  typedef Callback<Arg>CallbackType;
+
+ public:
+  explicit EventQueue(EventDispatcher *dispatcher)
+    : EventQueueItem(dispatcher) {}
+
+  inline void AddCallback(CallbackType *cb) {
+    callback_list_.push_back(cb);
+  }
+
+  void RemoveCallback(CallbackType *cb) {
+    for (size_t event_idx = 0; event_idx < callback_list_.size(); ++event_idx) {
+      if (callback_list_[event_idx] == cb) {
+        callback_list_.erase(callback_list_.begin() + event_idx);
+        return;
+      }
+    }
+  }
+
+  void Dispatch() {
+    for (size_t event_idx = 0; event_idx < event_queue_.size(); ++event_idx)
+      for (size_t call_idx = 0; call_idx < callback_list_.size(); ++call_idx)
+        callback_list_[call_idx]->Run(event_queue_[event_idx]);
+    event_queue_.clear();
+  }
+
+  void AddEvent(Arg arg) {
+    event_queue_.push_back(arg);
+    AlertDispatcher();
+  }
+
+ private:
+  std::vector<CallbackType *> callback_list_;
+  std::vector<Arg> event_queue_;
+};
+
+// This is the main event dispatcher.  It contains a central instance, and
+// is the entity responsible for dispatching events out of all queues to
+// their listeners during the idle loop.
+class EventDispatcher {
+ public:
+  void DispatchEvents();
+  void ExecuteOnIdle();
+  void RegisterCallbackQueue(EventQueueItem *queue);
+  void UnregisterCallbackQueue(EventQueueItem *queue);
+ private:
+  std::vector<EventQueueItem*> queue_list_;
+};
+
+}  // namespace shill
+
+#endif  // SHILL_EVENT_