Bug 1431256 part 3: AccessibleHandler: When a client requests children, fetch them optimally using a single cross-process call. r=MarcoZ

This implements IEnumVARIANT locally using the new method provided by HandlerProvider.
This avoids marshaling full objects for text leaf accessibles (instead using HandlerTextLeaf), which is much faster.
It also avoids a pointless cross-process call to IEnumVARIANT::Reset (and possibly IEnumVARIANT::Clone).
Finally, it caches children after the first query so that clients (such as UI Automation) which walk children one by one don't incur separate cross-process calls for every child.

MozReview-Commit-ID: KUIXQoXxInQ

--HG--
extra : rebase_source : a6c0a56c2bb65e227f7c45eb1b767e7df19efa49

accessible/ipc/win/handler/AccessibleHandler.cpp

@@ -12,6 +12,7 @@
 
 #include "AccessibleHandler.h"
 #include "AccessibleHandlerControl.h"
+#include "HandlerChildEnumerator.h"
 #include "HandlerRelation.h"
 
 #include "Factory.h"
@@ -406,6 +407,13 @@ AccessibleHandler::QueryHandlerInterface(IUnknown* aProxyUnknown, REFIID aIid,
     return S_OK;
   }
 
+  if (aIid == IID_IEnumVARIANT && mCachedData.mGeckoBackChannel) {
+    RefPtr<IEnumVARIANT> childEnum(
+      new HandlerChildEnumerator(this, mCachedData.mGeckoBackChannel));
+    childEnum.forget(aOutInterface);
+    return S_OK;
+  }
+
   return E_NOINTERFACE;
 }
 

accessible/ipc/win/handler/HandlerChildEnumerator.cpp

@@ -0,0 +1,183 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#if defined(MOZILLA_INTERNAL_API)
+#error This code is NOT for internal Gecko use!
+#endif // defined(MOZILLA_INTERNAL_API)
+
+#include "HandlerChildEnumerator.h"
+#include "HandlerTextLeaf.h"
+#include "mozilla/Assertions.h"
+
+namespace mozilla {
+namespace a11y {
+
+HandlerChildEnumerator::HandlerChildEnumerator(AccessibleHandler* aHandler,
+    IGeckoBackChannel* aGeckoBackChannel)
+  : mHandler(aHandler)
+  , mGeckoBackChannel(aGeckoBackChannel)
+  , mChildCount(0)
+  , mNextChild(0)
+{
+  MOZ_ASSERT(aHandler);
+  MOZ_ASSERT(aGeckoBackChannel);
+}
+
+HandlerChildEnumerator::HandlerChildEnumerator(
+    const HandlerChildEnumerator& aEnumerator)
+  : mHandler(aEnumerator.mHandler)
+  , mGeckoBackChannel(aEnumerator.mGeckoBackChannel)
+  , mChildCount(aEnumerator.mChildCount)
+  , mNextChild(aEnumerator.mNextChild)
+{
+  if (mChildCount == 0) {
+    return;
+  }
+  mChildren = MakeUnique<VARIANT[]>(mChildCount);
+  CopyMemory(mChildren.get(), aEnumerator.mChildren.get(),
+             sizeof(VARIANT) * mChildCount);
+  for (ULONG index = 0; index < mChildCount; ++index) {
+    mChildren[index].pdispVal->AddRef();
+  }
+}
+
+HandlerChildEnumerator::~HandlerChildEnumerator()
+{
+  ClearCache();
+}
+
+void
+HandlerChildEnumerator::ClearCache()
+{
+  if (!mChildren) {
+    return;
+  }
+
+  for (ULONG index = 0; index < mChildCount; ++index) {
+    mChildren[index].pdispVal->Release();
+  }
+
+  mChildren = nullptr;
+  mChildCount = 0;
+}
+
+HRESULT
+HandlerChildEnumerator::MaybeCacheChildren()
+{
+  if (mChildren) {
+    // Already cached.
+    return S_OK;
+  }
+
+  AccChildData* children;
+  HRESULT hr = mGeckoBackChannel->get_AllChildren(&children, &mChildCount);
+  if (FAILED(hr)) {
+    mChildCount = 0;
+    ClearCache();
+    return hr;
+  }
+
+  HWND hwnd = nullptr;
+  hr = mHandler->get_windowHandle(&hwnd);
+  MOZ_ASSERT(SUCCEEDED(hr));
+
+  RefPtr<IDispatch> parent;
+  hr = mHandler->QueryInterface(IID_IDispatch, getter_AddRefs(parent));
+  MOZ_ASSERT(SUCCEEDED(hr));
+
+  mChildren = MakeUnique<VARIANT[]>(mChildCount);
+  for (ULONG index = 0; index < mChildCount; ++index) {
+    AccChildData& data = children[index];
+    VARIANT& child = mChildren[index];
+    if (data.mAccessible) {
+      RefPtr<IDispatch> disp;
+      hr = data.mAccessible->QueryInterface(IID_IDispatch,
+                                            getter_AddRefs(disp));
+      data.mAccessible->Release();
+      MOZ_ASSERT(SUCCEEDED(hr));
+      if (FAILED(hr)) {
+        child.vt = VT_EMPTY;
+        continue;
+      }
+      child.vt = VT_DISPATCH;
+      disp.forget(&child.pdispVal);
+    } else {
+      // Text leaf.
+      RefPtr<IDispatch> leaf(
+        new HandlerTextLeaf(parent, index, hwnd, data));
+      child.vt = VT_DISPATCH;
+      leaf.forget(&child.pdispVal);
+    }
+  }
+
+  ::CoTaskMemFree(children);
+  return S_OK;
+}
+
+IMPL_IUNKNOWN_QUERY_HEAD(HandlerChildEnumerator)
+IMPL_IUNKNOWN_QUERY_IFACE(IEnumVARIANT)
+IMPL_IUNKNOWN_QUERY_TAIL_AGGREGATED(mHandler)
+
+/*** IEnumVARIANT ***/
+
+HRESULT
+HandlerChildEnumerator::Clone(IEnumVARIANT** aPpEnum)
+{
+  RefPtr<HandlerChildEnumerator> newEnum(new HandlerChildEnumerator(*this));
+  newEnum.forget(aPpEnum);
+  return S_OK;
+}
+
+HRESULT
+HandlerChildEnumerator::Next(ULONG aCelt, VARIANT* aRgVar,
+                             ULONG* aPCeltFetched)
+{
+  if (!aRgVar || aCelt == 0) {
+    return E_INVALIDARG;
+  }
+
+  HRESULT hr = MaybeCacheChildren();
+  if (FAILED(hr)) {
+    return hr;
+  }
+
+  for (ULONG index = 0; index < aCelt; ++index) {
+    if (mNextChild >= mChildCount) {
+      // Less elements remaining than were requested.
+      if (aPCeltFetched) {
+        *aPCeltFetched = index;
+      }
+      return S_FALSE;
+    }
+    aRgVar[index] = mChildren[mNextChild];
+    aRgVar[index].pdispVal->AddRef();
+    ++mNextChild;
+  }
+  *aPCeltFetched = aCelt;
+  return S_OK;
+}
+
+HRESULT
+HandlerChildEnumerator::Reset()
+{
+  mNextChild = 0;
+  ClearCache();
+  return S_OK;
+}
+
+HRESULT
+HandlerChildEnumerator::Skip(ULONG aCelt)
+{
+  mNextChild += aCelt;
+  if (mNextChild > mChildCount) {
+    // Less elements remaining than the client requested to skip.
+    return S_FALSE;
+  }
+  return S_OK;
+}
+
+} // namespace a11y
+} // namespace mozilla

accessible/ipc/win/handler/HandlerChildEnumerator.h

@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#if defined(MOZILLA_INTERNAL_API)
+#error This code is NOT for internal Gecko use!
+#endif // defined(MOZILLA_INTERNAL_API)
+
+#ifndef mozilla_a11y_HandlerChildEnumerator_h
+#define mozilla_a11y_HandlerChildEnumerator_h
+
+#include "AccessibleHandler.h"
+#include "IUnknownImpl.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+namespace a11y {
+
+class HandlerChildEnumerator final : public IEnumVARIANT
+{
+public:
+  explicit HandlerChildEnumerator(AccessibleHandler* aHandler,
+                                  IGeckoBackChannel* aGeckoBackChannel);
+
+  DECL_IUNKNOWN
+
+  // IEnumVARIANT
+  STDMETHODIMP Clone(IEnumVARIANT** aPpEnum) override;
+  STDMETHODIMP Next(ULONG aCelt, VARIANT* aRgVar,
+                    ULONG* aPCeltFetched) override;
+  STDMETHODIMP Reset() override;
+  STDMETHODIMP Skip(ULONG aCelt) override;
+
+private:
+  explicit HandlerChildEnumerator(const HandlerChildEnumerator& aEnumerator);
+  ~HandlerChildEnumerator();
+  void ClearCache();
+  HRESULT MaybeCacheChildren();
+
+  RefPtr<AccessibleHandler> mHandler;
+  RefPtr<IGeckoBackChannel> mGeckoBackChannel;
+  UniquePtr<VARIANT[]> mChildren;
+  ULONG mChildCount;
+  ULONG mNextChild;
+};
+
+} // namespace a11y
+} // namespace mozilla
+
+#endif // mozilla_a11y_HandlerChildEnumerator_h

accessible/ipc/win/handler/moz.build

@@ -23,6 +23,7 @@ SOURCES += [
     '!HandlerData_p.c',
     'AccessibleHandler.cpp',
     'AccessibleHandlerControl.cpp',
+    'HandlerChildEnumerator.cpp',
     'HandlerRelation.cpp',
     'HandlerTextLeaf.cpp',
 ]