Add a CallbackRegistry class to base/ to manage callbacks

base/callback_list.h

+// Copyright 2013 The Chromium 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 BASE_CALLBACK_LIST_H_
+#define BASE_CALLBACK_LIST_H_
+
+#include <algorithm>
+#include <limits>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+
+///////////////////////////////////////////////////////////////////////////////
+//
+// OVERVIEW:
+//
+//   A container for a list of callbacks.  Unlike a normal STL vector or list,
+//   this container can be modified during iteration without invalidating the
+//   iterator.  So, it safely handles the case of an callback removing itself
+//   or other callback from the list while callbacks are being run.
+//
+// TYPICAL USAGE:
+//
+//   class MyWidget {
+//    public:
+//     ...
+//
+//     typedef base::Callback<void(const Foo&)> OnFooCallback;
+//
+//     base::Closure RegisterCallback(const OnFooCallback& cb) {
+//       return callback_list_.RegisterCallback(cb);
+//     }
+//
+//    private:
+//     void NotifyFoo(const Foo& foo) {
+//       callback_list_.Run(foo);
+//     }
+//
+//     CallbackList<Foo> callback_list_;
+//   };
+//
+//
+//  class MyWidgetListener {
+//    public:
+//
+//     MyWidgetListener::MyWidgetListener() {
+//       remove_foo_callback_ = MyWidget::GetCurrent()->RegisterCallback(
+//           base::Bind(&MyWidgetListener::OnFoo, this));
+//     }
+//
+//     MyWidgetListener::~MyWidgetListener() {
+//       remove_foo_callback_.Run();
+//     }
+//
+//     void OnFoo(const Foo& foo) {
+//       // Do something.
+//     }
+//
+//    private:
+//     base::Closure remove_foo_callback_;
+//   };
+//
+///////////////////////////////////////////////////////////////////////////////
+struct NoDetail {};
+
+template <typename Detail>
+class CallbackList {
+ public:
+  typedef base::Callback<void(const Detail&)> CallbackType;
+
+  // Enumeration of which callbacks are called.
+  enum NotificationType {
+    // Specifies that any callbacks added during notification are called.
+    // This is the default type if no type is provided to the constructor.
+    NOTIFY_ALL,
+
+    // Specifies that callbacks added while sending out notifications are not
+    // called.
+    NOTIFY_EXISTING_ONLY
+  };
+
+  CallbackList()
+      : active_iterator_count_(0),
+        type_(NOTIFY_ALL),
+        weak_factory_(this) {}
+
+  explicit CallbackList(NotificationType type)
+      : active_iterator_count_(0),
+        type_(type),
+        weak_factory_(this) {}
+
+  ~CallbackList() {
+    Compact();
+    DCHECK_EQ(0U, size());
+  }
+
+  // Add a callback to the list. A callback should not be added to
+  // the same list more than once. The returned closure (used to remove the
+  // callback from the list) is guaranteed to be safe to run.
+  base::Closure RegisterCallback(
+      const base::Callback<void(const Detail&)>& cb) {
+    DCHECK(!cb.is_null());
+    for (size_t i = 0; i < callbacks_.size(); i++) {
+      if (callbacks_[i].Equals(cb)) {
+        NOTREACHED() << "Callbacks can only be added once!";
+        return base::Bind(&base::DoNothing);
+      }
+    }
+    callbacks_.push_back(cb);
+    base::Closure removal_cb = base::Bind(
+        &CallbackList::RemoveCallback, GetWeakPtr(), cb);
+    return removal_cb;
+  }
+
+  // Remove an callback from the list if it is in the list.
+  void RemoveCallback(const base::Callback<void(const Detail&)>& cb) {

[awong, 2013/08/27 01:01:06]

Does this and HasCallback need to be exposed as public?

Seems like RegisterCallback returning a remove Closure makes this less
important.

+    for (size_t i = 0; i < callbacks_.size(); i++) {
+      if (callbacks_[i].Equals(cb)) {
+        if (active_iterator_count_)
+          callbacks_[i].Reset();
+        else

[awong, 2013/08/27 01:01:06]

I think style guide says you're supposed to use braces if you have an else
clause.

[Mark Mentovai, 2013/08/27 02:08:21]

awong wrote:
Nope. It says that if one side has braces, the other side needs it too. But
neither of these require braces, so they’re optional.

[awong, 2013/08/27 16:51:35]

Thanks for looking it up. Even so, in this case the lack of brace before the
return is making my eyes slightly wild. :-/

+          callbacks_.erase(callbacks_.begin() + i);
+        return;
+      }
+    }
+  }
+
+  bool HasCallback(const base::Callback<void(const Detail&)>& cb) const {
+    for (size_t i = 0; i < callbacks_.size(); ++i) {
+      if (callbacks_[i].Equals(cb))
+        return true;
+    }
+    return false;
+  }
+
+  void Run(const Detail& details) {
+    if (might_have_callbacks()) {
+      RunImpl(details);
+    }
+   }
+
+  void Clear() {
+    if (active_iterator_count_) {
+      for (size_t i = 0; i < callbacks_.size(); ++i) {
+        callbacks_[i].Reset();
+      }
+    } else {
+      callbacks_.clear();
+    }
+  }
+
+  bool might_have_callbacks() const {
+    return size() != 0;
+  }
+
+ private:
+  typedef std::vector<base::Callback<void(const Detail&)> > ListType;
+
+  // An iterator class that can be used to access the list of callbacks.
+  class Iterator {
+   public:
+    Iterator(CallbackList<Detail>* list)
+        : list_(list->GetWeakPtr()),
+          index_(0),
+          max_index_(list->type_ == NOTIFY_ALL ?
+                     std::numeric_limits<size_t>::max() :
+                     list->callbacks_.size()) {
+      ++list_->active_iterator_count_;
+    }
+
+    ~Iterator() {
+      if (list_.get() && --list_->active_iterator_count_ == 0)
+        list_->Compact();
+    }
+
+    base::Callback<void(const Detail&)> GetNext() {
+      if (!list_.get())
+        return base::Callback<void(const Detail&)>();
+      ListType& callbacks = list_->callbacks_;
+      size_t max_index = std::min(max_index_, callbacks.size());
+      while (index_ < max_index && callbacks[index_].is_null())
+        ++index_;
+      return index_ < max_index ? callbacks[index_++] :
+                                  base::Callback<void(const Detail&)>();
+    }
+
+   private:
+    base::WeakPtr<CallbackList<Detail> > list_;
+    size_t index_;
+    size_t max_index_;
+  };
+
+  base::WeakPtr<CallbackList<Detail> > GetWeakPtr() {
+    return weak_factory_.GetWeakPtr();
+  }
+
+  void Compact() {
+    size_t i = 0;
+    while (i < callbacks_.size()) {
+      if (callbacks_[i].is_null())
+        callbacks_.erase(callbacks_.begin() + i);
+      else
+        ++i;
+    }
+  }
+
+  // TODO(caitkp): Is there a better way to do this, while still keeping
+  // Iterator priavte?
+  void RunImpl(const Detail& details) {
+      Iterator it(this);
+      CallbackType cb;
+      while(!(cb = it.GetNext()).is_null())
+        cb.Run(details);
+  }
+  size_t size() const { return callbacks_.size(); }
+
+  ListType callbacks_;
+  int active_iterator_count_;
+  NotificationType type_;
+  base::WeakPtrFactory<CallbackList<Detail> > weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(CallbackList);
+};
+
+// TODO(caitkp): Figure out how to share implementation so we don't have to
+// rewrite the whole class in the specialization.
+/*template <>
+class CallbackList<NoDetail> {

[awong, 2013/08/27 01:01:06]

Hmm...thinking back on the mess between scoped_ptr and scoped_array, it actually
might not be possible.  That actually might be a reason for a base class (that
you'd want to stuff in the internal namespace).  Can that be made to work?

I'll look at it more tomorrow morning.

+ public:
+   void Run() {
+    // Specialization for NoDetails has do Run method.
+    if (CallbackList<NoDetail>::might_have_callbacks())
+      RunImpl(NoDetail());
+   }
+};
+*/
+
+#endif  // BASE_CALLBACK_LIST_H_