gecko-dev/devtools/shared/heapsnapshot/DominatorTree.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
/* 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/. */

#include "mozilla/devtools/DominatorTree.h"
#include "mozilla/dom/DominatorTreeBinding.h"

namespace mozilla {
namespace devtools {

dom::Nullable<uint64_t> DominatorTree::GetRetainedSize(uint64_t aNodeId,
                                                       ErrorResult& aRv) {
  JS::ubi::Node::Id id(aNodeId);
  auto node = mHeapSnapshot->getNodeById(id);
  if (node.isNothing()) return dom::Nullable<uint64_t>();

  auto mallocSizeOf = GetCurrentThreadDebuggerMallocSizeOf();
  JS::ubi::Node::Size size = 0;
  if (!mDominatorTree.getRetainedSize(*node, mallocSizeOf, size)) {
    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
    return dom::Nullable<uint64_t>();
  }

  MOZ_ASSERT(size != 0,
             "The node should not have been unknown since we got it from the "
             "heap snapshot.");
  return dom::Nullable<uint64_t>(size);
}

struct NodeAndRetainedSize {
  JS::ubi::Node mNode;
  JS::ubi::Node::Size mSize;

  NodeAndRetainedSize(const JS::ubi::Node& aNode, JS::ubi::Node::Size aSize)
      : mNode(aNode), mSize(aSize) {}

  struct Comparator {
    static bool Equals(const NodeAndRetainedSize& aLhs,
                       const NodeAndRetainedSize& aRhs) {
      return aLhs.mSize == aRhs.mSize;
    }

    static bool LessThan(const NodeAndRetainedSize& aLhs,
                         const NodeAndRetainedSize& aRhs) {
      // Use > because we want to sort from greatest to least retained size.
      return aLhs.mSize > aRhs.mSize;
    }
  };
};

void DominatorTree::GetImmediatelyDominated(
    uint64_t aNodeId, dom::Nullable<nsTArray<uint64_t>>& aOutResult,
    ErrorResult& aRv) {
  MOZ_ASSERT(aOutResult.IsNull());

  JS::ubi::Node::Id id(aNodeId);
  Maybe<JS::ubi::Node> node = mHeapSnapshot->getNodeById(id);
  if (node.isNothing()) return;

  // Get all immediately dominated nodes and their retained sizes.
  MallocSizeOf mallocSizeOf = GetCurrentThreadDebuggerMallocSizeOf();
  Maybe<JS::ubi::DominatorTree::DominatedSetRange> range =
      mDominatorTree.getDominatedSet(*node);
  MOZ_ASSERT(
      range.isSome(),
      "The node should be known, since we got it from the heap snapshot.");
  size_t length = range->length();
  nsTArray<NodeAndRetainedSize> dominatedNodes(length);
  for (const JS::ubi::Node& dominatedNode : *range) {
    JS::ubi::Node::Size retainedSize = 0;
    if (NS_WARN_IF(!mDominatorTree.getRetainedSize(dominatedNode, mallocSizeOf,
                                                   retainedSize))) {
      aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
      return;
    }
    MOZ_ASSERT(retainedSize != 0,
               "retainedSize should not be zero since we know the node is in "
               "the dominator tree.");

    dominatedNodes.AppendElement(
        NodeAndRetainedSize(dominatedNode, retainedSize));
  }

  // Sort them by retained size.
  NodeAndRetainedSize::Comparator comparator;
  dominatedNodes.Sort(comparator);

  // Fill the result with the nodes' ids.
  JS::ubi::Node root = mDominatorTree.root();
  aOutResult.SetValue(nsTArray<uint64_t>(length));
  for (const NodeAndRetainedSize& entry : dominatedNodes) {
    // The root dominates itself, but we don't want to expose that to JS.
    if (entry.mNode == root) continue;

    aOutResult.Value().AppendElement(entry.mNode.identifier());
  }
}

dom::Nullable<uint64_t> DominatorTree::GetImmediateDominator(
    uint64_t aNodeId) const {
  JS::ubi::Node::Id id(aNodeId);
  Maybe<JS::ubi::Node> node = mHeapSnapshot->getNodeById(id);
  if (node.isNothing()) return dom::Nullable<uint64_t>();

  JS::ubi::Node dominator = mDominatorTree.getImmediateDominator(*node);
  if (!dominator || dominator == *node) return dom::Nullable<uint64_t>();

  return dom::Nullable<uint64_t>(dominator.identifier());
}

/*** Cycle Collection Boilerplate
 * *****************************************************************/

NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(DominatorTree, mParent, mHeapSnapshot)

NS_IMPL_CYCLE_COLLECTING_ADDREF(DominatorTree)
NS_IMPL_CYCLE_COLLECTING_RELEASE(DominatorTree)

NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(DominatorTree)
  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
  NS_INTERFACE_MAP_ENTRY(nsISupports)
NS_INTERFACE_MAP_END

/* virtual */
JSObject* DominatorTree::WrapObject(JSContext* aCx,
                                    JS::HandleObject aGivenProto) {
  return dom::DominatorTree_Binding::Wrap(aCx, this, aGivenProto);
}

}  // namespace devtools
}  // namespace mozilla