Introduce MIDIInputMap and MIDIOutputMap.

Source/modules/webmidi/MIDIPortMap.h

+// Copyright 2014 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 MIDIPortMap_h
+#define MIDIPortMap_h
+
+#include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/ScriptState.h"
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/V8Binding.h"
+#include "core/dom/Iterator.h"
+#include "platform/heap/Handle.h"
+#include "wtf/HashMap.h"
+#include "wtf/text/StringHash.h"
+#include "wtf/text/WTFString.h"
+
+namespace blink {
+
+template <typename T>
+class MIDIPortMap : public GarbageCollected<MIDIPortMap<T> > {
+public:
+    MIDIPortMap(const HeapHashMap<String, Member<T> >& entries) : m_entries(entries) { }
+
+    // IDL attributes / methods
+    size_t size() const { return m_entries.size(); }
+    Iterator* keys();
+    Iterator* entries();
+    Iterator* values();
+    T* get(const String& key) const;
+    bool has(const String& key) const { return m_entries.contains(key); }
+    Iterator* iterator(ScriptState*, ExceptionState&) { return values(); }
+
+    void trace(Visitor* visitor)
+    {
+        visitor->trace(m_entries);
+    }
+
+private:
+    typedef HeapHashMap<String, Member<T> > MapType;
+    typedef typename HeapHashMap<String, Member<T> >::const_iterator IteratorType;
+    struct KeySelector {
+        static const String& select(ScriptState*, IteratorType i) { return i->key; }
+    };
+    struct ValueSelector {
+        static T* select(ScriptState*, IteratorType i) { return i->value; }
+    };
+    struct EntrySelector {
+        static Vector<ScriptValue> select(ScriptState* scriptState, IteratorType i)
+        {
+            Vector<ScriptValue> entry;
+            entry.append(ScriptValue(scriptState, v8String(scriptState->isolate(), i->key)));
+            entry.append(ScriptValue(scriptState, V8ValueTraits<T*>::toV8Value(i->value, scriptState->context()->Global(), scriptState->isolate())));
+            return entry;
+        }
+    };
+
+    // Note: This template class relies on the fact that m_map.m_entries will
+    // never be modified once it is created.
+    template <typename Selector>
+    class MapIterator : public Iterator {
+    public:
+        MapIterator(MIDIPortMap<T>* map, IteratorType iterator, IteratorType end)
+            : m_map(map)
+            , m_iterator(iterator)
+            , m_end(end) { }
+
+        virtual ScriptValue next(ScriptState* scriptState, ExceptionState&) OVERRIDE
+        {
+            if (m_iterator == m_end)
+                return ScriptValue(scriptState, v8DoneIteratorResult(scriptState->isolate()));
+            ScriptValue result(scriptState, v8IteratorResult(scriptState, Selector::select(scriptState, m_iterator)));
+            ++m_iterator;
+            return result;
+        }
+
+        virtual ScriptValue next(ScriptState*, ScriptValue, ExceptionState& exceptionState) OVERRIDE
+        {
+            exceptionState.throwDOMException(InvalidModificationError, "Not implemented");

[haraken, 2014/08/31 07:18:57]

Just help me understand: Is there any way for user's script to reach this code?

If yes, I think it's problematic. If no, can we change this to
ASSERT_NOT_REACHED()?

[yhirano, 2014/09/01 02:22:11]

Yes, it can be called from a script. See [1]. It is intended to used with
yield[2], but we can call it manually.

1: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-iteratornext
2:
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generator-function-...

I don't understand why it is problematic: can you explain?

[haraken, 2014/09/01 07:17:48]

I just thought it would be problematic to expose "Not implemented" features to
outside. Wouldn't it be a concern for WebMIDI?

[yhirano, 2014/09/01 11:32:52]

I reread the spec and found ignoring the parameter was the desired behavior
here. Fixed.

+            return ScriptValue();
+        }
+
+        virtual void trace(Visitor* visitor) OVERRIDE
+        {
+            visitor->trace(m_map);
+            Iterator::trace(visitor);
+        }
+
+    private:
+        // m_map is stored just for keeping it alive.
+        const Member<const MIDIPortMap<T> > m_map;

[haraken, 2014/08/31 07:18:57]

Why do we need this? trace(m_entries) in MIDIPortMap is not enough to keep the
map alive?

[yhirano, 2014/09/01 02:22:11]

Scripts can hold iterators independently. i.e. you can write a script like this:

 // |map| is backed by MIDIPortMap.
 var i = map[Symbol.iterator]();
 map = undefined;

Here we must not release the MIDIPortMap::m_entries because the iterator uses it
while it is not reachable via |map|.

 

[haraken, 2014/09/01 07:17:48]

Makes sense. A comment about it will be helpful.

// The map needs to be kept alive while JavaScript holds the iterator to the
map.

[yhirano, 2014/09/01 11:32:52]

Done.

+        IteratorType m_iterator;
+        const IteratorType m_end;
+    };
+
+    const MapType m_entries;
+};
+
+template <typename T>
+Iterator* MIDIPortMap<T>::keys()
+{
+    return new MapIterator<KeySelector>(this, m_entries.begin(), m_entries.end());
+}
+
+template <typename T>
+Iterator* MIDIPortMap<T>::entries()
+{
+    return new MapIterator<EntrySelector>(this, m_entries.begin(), m_entries.end());
+}
+
+template <typename T>
+Iterator* MIDIPortMap<T>::values()
+{
+    return new MapIterator<ValueSelector>(this, m_entries.begin(), m_entries.end());
+}
+
+template <typename T>
+T* MIDIPortMap<T>::get(const String& key) const
+{
+    return has(key) ? m_entries.get(key) : 0;
+}
+
+} // namespace blink
+
+#endif