tubestation/toolkit/devtools/server/DeserializedNode.h

/* -*-  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/. */

#ifndef mozilla_devtools_DeserializedNode__
#define mozilla_devtools_DeserializedNode__

#include "js/UbiNode.h"
#include "mozilla/devtools/CoreDump.pb.h"
#include "mozilla/MaybeOneOf.h"
#include "mozilla/Move.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/Vector.h"

// `Deserialized{Node,Edge}` translate protobuf messages from our core dump
// format into structures we can rely upon for implementing `JS::ubi::Node`
// specializations on top of. All of the properties of the protobuf messages are
// optional for future compatibility, and this is the layer where we validate
// that the properties that do actually exist in any given message fulfill our
// semantic requirements.
//
// Both `DeserializedNode` and `DeserializedEdge` are always owned by a
// `HeapSnapshot` instance, and their lifetimes must not extend after that of
// their owning `HeapSnapshot`.

namespace mozilla {
namespace devtools {

class HeapSnapshot;

using NodeId = uint64_t;

// A `DeserializedEdge` represents an edge in the heap graph pointing to the
// node with id equal to `DeserializedEdge::referent` that we deserialized from
// a core dump.
struct DeserializedEdge {
  NodeId         referent;
  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
  const char16_t* name;

  explicit DeserializedEdge();
  DeserializedEdge(DeserializedEdge&& rhs);
  DeserializedEdge& operator=(DeserializedEdge&& rhs);

  // Initialize this `DeserializedEdge` from the given `protobuf::Edge` message.
  bool init(const protobuf::Edge& edge, HeapSnapshot& owner);

private:
  DeserializedEdge(const DeserializedEdge&) = delete;
  DeserializedEdge& operator=(const DeserializedEdge&) = delete;
};

// A `DeserializedNode` is a node in the heap graph that we deserialized from a
// core dump.
struct DeserializedNode {
  using EdgeVector = Vector<DeserializedEdge>;
  using UniqueStringPtr = UniquePtr<char16_t[]>;

  NodeId          id;
  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
  const char16_t* typeName;
  uint64_t        size;
  EdgeVector      edges;
  // A weak pointer to this node's owning `HeapSnapshot`. Safe without
  // AddRef'ing because this node's lifetime is equal to that of its owner.
  HeapSnapshot*   owner;

  DeserializedNode(NodeId id,
                   const char16_t* typeName,
                   uint64_t size,
                   EdgeVector&& edges,
                   HeapSnapshot& owner)
    : id(id)
    , typeName(typeName)
    , size(size)
    , edges(Move(edges))
    , owner(&owner)
  { }
  virtual ~DeserializedNode() { }

  DeserializedNode(DeserializedNode&& rhs);
  DeserializedNode& operator=(DeserializedNode&& rhs);

  // Get a borrowed reference to the given edge's referent. This method is
  // virtual to provide a hook for gmock and gtest.
  virtual JS::ubi::Node getEdgeReferent(const DeserializedEdge& edge);

  struct HashPolicy;

protected:
  // This is only for use with `MockDeserializedNode` in testing.
  DeserializedNode(NodeId id, const char16_t* typeName, uint64_t size);

private:
  DeserializedNode(const DeserializedNode&) = delete;
  DeserializedNode& operator=(const DeserializedNode&) = delete;
};

struct DeserializedNode::HashPolicy
{
  using Lookup = NodeId;

  static js::HashNumber hash(const Lookup& lookup) {
    // NodeIds are always 64 bits, but they are derived from the original
    // referents' addresses, which could have been either 32 or 64 bits long.
    // As such, a NodeId has little entropy in its bottom three bits, and may or
    // may not have entropy in its upper 32 bits. This hash should manage both
    // cases well.
    uint64_t id = lookup >> 3;
    return js::HashNumber((id >> 32) ^ id);
  }

  static bool match(const DeserializedNode& existing, const Lookup& lookup) {
    return existing.id == lookup;
  }
};

} // namespace devtools
} // namespace mozilla

namespace JS {
namespace ubi {

using mozilla::devtools::DeserializedNode;
using mozilla::UniquePtr;

template<>
struct Concrete<DeserializedNode> : public Base
{
protected:
  explicit Concrete(DeserializedNode* ptr) : Base(ptr) { }
  DeserializedNode& get() const {
    return *static_cast<DeserializedNode*>(ptr);
  }

public:
  static const char16_t concreteTypeName[];

  static void construct(void* storage, DeserializedNode* ptr) {
    new (storage) Concrete(ptr);
  }

  Id identifier() const override { return get().id; }
  bool isLive() const override { return false; }
  const char16_t* typeName() const override;
  size_t size(mozilla::MallocSizeOf mallocSizeof) const override;

  // We ignore the `bool wantNames` parameter because we can't control whether
  // the core dump was serialized with edge names or not.
  UniquePtr<EdgeRange> edges(JSContext* cx, bool) const override;
};

} // namespace ubi
} // namespace JS

#endif // mozilla_devtools_DeserializedNode__