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 // Copyright 2010 the V8 project 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 V8_V8_PROFILER_H_
 #define V8_V8_PROFILER_H_
 
 #include <limits.h>
 
 #include <memory>
 #include <unordered_set>
 #include <vector>
 
 #include "cppgc/common.h"          // NOLINT(build/include_directory)
 #include "v8-local-handle.h"       // NOLINT(build/include_directory)
 #include "v8-message.h"            // NOLINT(build/include_directory)
 #include "v8-persistent-handle.h"  // NOLINT(build/include_directory)
 
 /**
  * Profiler support for the V8 JavaScript engine.
  */
 namespace v8 {
 
 enum class EmbedderStateTag : uint8_t;
 class HeapGraphNode;
 struct HeapStatsUpdate;
 class Object;
 enum StateTag : uint16_t;
 
 using NativeObject = void*;
 using SnapshotObjectId = uint32_t;
 using ProfilerId = uint32_t;
 
 struct CpuProfileDeoptFrame {
   int script_id;
   size_t position;
 };
 
 namespace internal {
 class CpuProfile;
 }  // namespace internal
 
 }  // namespace v8
 
 #ifdef V8_OS_WIN
 template class V8_EXPORT std::vector<v8::CpuProfileDeoptFrame>;
 #endif
 
 namespace v8 {
 
 /**
  * Identifies which component initiated CPU profiling for proper attribution.
  */
 enum class CpuProfileSource : uint8_t {
   /** Default value when no explicit source is specified. */
   kUnspecified = 0,
   /** Profiling initiated via the DevTools Inspector protocol. */
   kInspector = 1,
   /** Profiling initiated by the embedder (e.g., Blink) via self-profiling API.
    */
   kSelfProfiling = 2,
   /** Profiling initiated internally by V8 (e.g., tracing CPU profiler). */
   kInternal = 3,
 };
 
 struct V8_EXPORT CpuProfileDeoptInfo {
   /** A pointer to a static string owned by v8. */
   const char* deopt_reason;
   std::vector<CpuProfileDeoptFrame> stack;
 };
 
 }  // namespace v8
 
 #ifdef V8_OS_WIN
 template class V8_EXPORT std::vector<v8::CpuProfileDeoptInfo>;
 #endif
 
 namespace v8 {
 
 /**
  * CpuProfileNode represents a node in a call graph.
  */
 class V8_EXPORT CpuProfileNode {
  public:
   struct LineTick {
     /** The 1-based number of the source line where the function originates. */
     int line;
 
     /** The 1-based number of the source column where the function originates.
      */
     int column;
 
     /** The count of samples associated with the source line. */
     unsigned int hit_count;
   };
 
   // An annotation hinting at the source of a CpuProfileNode.
   enum SourceType {
     // User-supplied script with associated resource information.
     kScript = 0,
     // Native scripts and provided builtins.
     kBuiltin = 1,
     // Callbacks into native code.
     kCallback = 2,
     // VM-internal functions or state.
     kInternal = 3,
     // A node that failed to symbolize.
     kUnresolved = 4,
   };
 
   /** Returns function name (empty string for anonymous functions.) */
   Local<String> GetFunctionName() const;
 
   /**
    * Returns function name (empty string for anonymous functions.)
    * The string ownership is *not* passed to the caller. It stays valid until
    * profile is deleted. The function is thread safe.
    */
   const char* GetFunctionNameStr() const;
 
   /** Returns id of the script where function is located. */
   int GetScriptId() const;
 
   /** Returns resource name for script from where the function originates. */
   Local<String> GetScriptResourceName() const;
 
   /**
    * Returns resource name for script from where the function originates.
    * The string ownership is *not* passed to the caller. It stays valid until
    * profile is deleted. The function is thread safe.
    */
   const char* GetScriptResourceNameStr() const;
 
   /**
    * Return true if the script from where the function originates is flagged as
    * being shared cross-origin.
    */
   bool IsScriptSharedCrossOrigin() const;
 
   /**
    * Returns the number, 1-based, of the line where the function originates.
    * kNoLineNumberInfo if no line number information is available.
    */
   int GetLineNumber() const;
 
   /**
    * Returns 1-based number of the column where the function originates.
    * kNoColumnNumberInfo if no column number information is available.
    */
   int GetColumnNumber() const;
 
   /**
    * Returns the number of the function's source lines that collect the samples.
    */
   unsigned int GetHitLineCount() const;
 
   /** Returns the set of source lines that collect the samples.
    *  The caller allocates buffer and responsible for releasing it.
    *  True if all available entries are copied, otherwise false.
    *  The function copies nothing if buffer is not large enough.
    */
   bool GetLineTicks(LineTick* entries, unsigned int length) const;
 
   /** Returns bailout reason for the function
     * if the optimization was disabled for it.
     */
   const char* GetBailoutReason() const;
 
   /**
     * Returns the count of samples where the function was currently executing.
     */
   unsigned GetHitCount() const;
 
   /** Returns id of the node. The id is unique within the tree */
   unsigned GetNodeId() const;
 
   /**
    * Gets the type of the source which the node was captured from.
    */
   SourceType GetSourceType() const;
 
   /** Returns child nodes count of the node. */
   int GetChildrenCount() const;
 
   /** Retrieves a child node by index. */
   const CpuProfileNode* GetChild(int index) const;
 
   /** Retrieves the ancestor node, or null if the root. */
   const CpuProfileNode* GetParent() const;
 
   /** Retrieves deopt infos for the node. */
   const std::vector<CpuProfileDeoptInfo>& GetDeoptInfos() const;
 
   static const int kNoLineNumberInfo = Message::kNoLineNumberInfo;
   static const int kNoColumnNumberInfo = Message::kNoColumnInfo;
 };
 
 /**
  * An interface for exporting data from V8, using "push" model.
  */
 class V8_EXPORT OutputStream {
  public:
   enum WriteResult { kContinue = 0, kAbort = 1 };
   virtual ~OutputStream() = default;
   /** Notify about the end of stream. */
   virtual void EndOfStream() = 0;
   /** Get preferred output chunk size. Called only once. */
   virtual int GetChunkSize() { return 1024; }
   /**
    * Writes the next chunk of snapshot data into the stream. Writing
    * can be stopped by returning kAbort as function result. EndOfStream
    * will not be called in case writing was aborted.
    */
   virtual WriteResult WriteAsciiChunk(char* data, int size) = 0;
   /**
    * Writes the next chunk of heap stats data into the stream. Writing
    * can be stopped by returning kAbort as function result. EndOfStream
    * will not be called in case writing was aborted.
    */
   virtual WriteResult WriteHeapStatsChunk(HeapStatsUpdate* data, int count) {
     return kAbort;
   }
 };
 
 /**
  * CpuProfile contains a CPU profile in a form of top-down call tree
  * (from main() down to functions that do all the work).
  */
 class V8_EXPORT CpuProfile {
  public:
   enum SerializationFormat {
     kJSON = 0  // See format description near 'Serialize' method.
   };
   /** Returns CPU profile title. */
   Local<String> GetTitle() const;
 
   /** Returns the root node of the top down call tree. */
   const CpuProfileNode* GetTopDownRoot() const;
 
   /**
    * Returns number of samples recorded. The samples are not recorded unless
    * |record_samples| parameter of CpuProfiler::StartCpuProfiling is true.
    */
   int GetSamplesCount() const;
 
   /**
    * Returns profile node corresponding to the top frame the sample at
    * the given index.
    */
   const CpuProfileNode* GetSample(int index) const;
 
   /**
    * Returns the timestamp of the sample. The timestamp is the number of
    * microseconds since some unspecified starting point.
    * The point is equal to the starting point used by GetStartTime.
    */
   int64_t GetSampleTimestamp(int index) const;
 
   /**
    * Returns time when the profile recording was started (in microseconds)
    * since some unspecified starting point.
    */
   int64_t GetStartTime() const;
 
   /**
    * Returns state of the vm when sample was captured.
    */
   StateTag GetSampleState(int index) const;
 
   /**
    * Returns state of the embedder when sample was captured.
    */
   EmbedderStateTag GetSampleEmbedderState(int index) const;
 
   /**
    * Returns time when the profile recording was stopped (in microseconds)
    * since some unspecified starting point.
    * The point is equal to the starting point used by GetStartTime.
    */
   int64_t GetEndTime() const;
 
   /**
    * Deletes the profile and removes it from CpuProfiler's list.
    * All pointers to nodes previously returned become invalid.
    */
   void Delete();
 
   /**
    * Prepare a serialized representation of the profile. The result
    * is written into the stream provided in chunks of specified size.
    *
    * For the JSON format, heap contents are represented as an object
    * with the following structure:
    *
    *  {
    *    nodes: [nodes array],
    *    startTime: number,
    *    endTime: number
    *    samples: [strings array]
    *    timeDeltas: [numbers array]
    *  }
    *
    */
   void Serialize(OutputStream* stream,
                  SerializationFormat format = kJSON) const;
 };
 
 enum CpuProfilingMode {
   // In the resulting CpuProfile tree, intermediate nodes in a stack trace
   // (from the root to a leaf) will have line numbers that point to the start
   // line of the function, rather than the line of the callsite of the child.
   kLeafNodeLineNumbers,
   // In the resulting CpuProfile tree, nodes are separated based on the line
   // number of their callsite in their parent.
   kCallerLineNumbers,
 };
 
 // Determines how names are derived for functions sampled.
 enum CpuProfilingNamingMode {
   // Use the immediate name of functions at compilation time.
   kStandardNaming,
   // Use more verbose naming for functions without names, inferred from scope
   // where possible.
   kDebugNaming,
 };
 
 enum CpuProfilingLoggingMode {
   // Enables logging when a profile is active, and disables logging when all
   // profiles are detached.
   kLazyLogging,
   // Enables logging for the lifetime of the CpuProfiler. Calls to
   // StartRecording are faster, at the expense of runtime overhead.
   kEagerLogging,
 };
 
 // Enum for returning profiling status. Once StartProfiling is called,
 // we want to return to clients whether the profiling was able to start
 // correctly, or return a descriptive error.
 enum class CpuProfilingStatus {
   kStarted,
   kAlreadyStarted,
   kErrorTooManyProfilers
 };
 
 /**
  * Result from StartProfiling returning the Profiling Status, and
  * id of the started profiler, or 0 if profiler is not started
  */
 struct CpuProfilingResult {
   const ProfilerId id;
   const CpuProfilingStatus status;
 };
 
 /**
  * Delegate for when max samples reached and samples are discarded.
  */
 class V8_EXPORT DiscardedSamplesDelegate {
  public:
   DiscardedSamplesDelegate() = default;
 
   virtual ~DiscardedSamplesDelegate() = default;
   virtual void Notify() = 0;
 
   ProfilerId GetId() const { return profiler_id_; }
 
  private:
   friend internal::CpuProfile;
 
   void SetId(ProfilerId id) { profiler_id_ = id; }
 
   ProfilerId profiler_id_;
 };
 
 /**
  * Optional profiling attributes.
  */
 class V8_EXPORT CpuProfilingOptions {
  public:
   // Indicates that the sample buffer size should not be explicitly limited.
   static const unsigned kNoSampleLimit = UINT_MAX;
 
   /**
    * \param mode Type of computation of stack frame line numbers.
    * \param max_samples The maximum number of samples that should be recorded by
    *                    the profiler. Samples obtained after this limit will be
    *                    discarded.
    * \param sampling_interval_us controls the profile-specific target
    *                             sampling interval. The provided sampling
    *                             interval will be snapped to the next lowest
    *                             non-zero multiple of the profiler's sampling
    *                             interval, set via SetSamplingInterval(). If
    *                             zero, the sampling interval will be equal to
    *                             the profiler's sampling interval.
    * \param filter_context If specified, profiles will only contain frames
    *                       using this context. Other frames will be elided.
    * \param profile_source Identifies the source of this CPU profile.
    */
   CpuProfilingOptions(
       CpuProfilingMode mode = kLeafNodeLineNumbers,
       unsigned max_samples = kNoSampleLimit, int sampling_interval_us = 0,
       MaybeLocal<Context> filter_context = MaybeLocal<Context>(),
       CpuProfileSource profile_source = CpuProfileSource::kUnspecified);
 
   CpuProfilingOptions(CpuProfilingOptions&&) = default;
   CpuProfilingOptions& operator=(CpuProfilingOptions&&) = default;
 
   CpuProfilingMode mode() const { return mode_; }
   unsigned max_samples() const { return max_samples_; }
   int sampling_interval_us() const { return sampling_interval_us_; }
   CpuProfileSource profile_source() const { return profile_source_; }
 
  private:
   friend class internal::CpuProfile;
 
   bool has_filter_context() const { return !filter_context_.IsEmpty(); }
   void* raw_filter_context() const;
 
   CpuProfilingMode mode_;
   unsigned max_samples_;
   int sampling_interval_us_;
   Global<Context> filter_context_;
   CpuProfileSource profile_source_;
 };
 
 /**
  * Interface for controlling CPU profiling. Instance of the
  * profiler can be created using v8::CpuProfiler::New method.
  */
 class V8_EXPORT CpuProfiler {
  public:
   /**
    * Creates a new CPU profiler for the |isolate|. The isolate must be
    * initialized. The profiler object must be disposed after use by calling
    * |Dispose| method.
    */
   static CpuProfiler* New(Isolate* isolate,
                           CpuProfilingNamingMode = kDebugNaming,
                           CpuProfilingLoggingMode = kLazyLogging);
 
   /**
    * Synchronously collect current stack sample in all profilers attached to
    * the |isolate|. The call does not affect number of ticks recorded for
    * the current top node.
    * |trace_id| is an optional identifier set to the collected sample.
    * this is useful to associate the sample with a trace event.
    */
   static void CollectSample(
       Isolate* isolate, const std::optional<uint64_t> trace_id = std::nullopt);
 
   /**
    * Disposes the CPU profiler object.
    */
   void Dispose();
 
   /**
    * Changes default CPU profiler sampling interval to the specified number
    * of microseconds. Default interval is 1000us. This method must be called
    * when there are no profiles being recorded.
    */
   void SetSamplingInterval(int us);
 
   /**
    * Sets whether or not the profiler should prioritize consistency of sample
    * periodicity on Windows. Disabling this can greatly reduce CPU usage, but
    * may result in greater variance in sample timings from the platform's
    * scheduler. Defaults to enabled. This method must be called when there are
    * no profiles being recorded.
    */
   void SetUsePreciseSampling(bool);
 
   /**
    * Starts collecting a CPU profile. Several profiles may be collected at once.
    * Generates an anonymous profiler, without a String identifier.
    */
   CpuProfilingResult Start(
       CpuProfilingOptions options,
       std::unique_ptr<DiscardedSamplesDelegate> delegate = nullptr);
 
   /**
    * Starts collecting a CPU profile. Title may be an empty string. Several
    * profiles may be collected at once. Attempts to start collecting several
    * profiles with the same title are silently ignored.
    */
   CpuProfilingResult Start(
       Local<String> title, CpuProfilingOptions options,
       std::unique_ptr<DiscardedSamplesDelegate> delegate = nullptr);
 
   /**
    * Starts profiling with the same semantics as above, except with expanded
    * parameters.
    *
    * |record_samples| parameter controls whether individual samples should
    * be recorded in addition to the aggregated tree.
    *
    * |max_samples| controls the maximum number of samples that should be
    * recorded by the profiler. Samples obtained after this limit will be
    * discarded.
    */
   CpuProfilingResult Start(
       Local<String> title, CpuProfilingMode mode, bool record_samples = false,
       unsigned max_samples = CpuProfilingOptions::kNoSampleLimit);
 
   /**
    * The same as StartProfiling above, but the CpuProfilingMode defaults to
    * kLeafNodeLineNumbers mode, which was the previous default behavior of the
    * profiler.
    */
   CpuProfilingResult Start(Local<String> title, bool record_samples = false);
 
   /**
    * Starts collecting a CPU profile. Title may be an empty string. Several
    * profiles may be collected at once. Attempts to start collecting several
    * profiles with the same title are silently ignored.
    */
   CpuProfilingStatus StartProfiling(
       Local<String> title, CpuProfilingOptions options,
       std::unique_ptr<DiscardedSamplesDelegate> delegate = nullptr);
 
   /**
    * Starts profiling with the same semantics as above, except with expanded
    * parameters.
    *
    * |record_samples| parameter controls whether individual samples should
    * be recorded in addition to the aggregated tree.
    *
    * |max_samples| controls the maximum number of samples that should be
    * recorded by the profiler. Samples obtained after this limit will be
    * discarded.
    */
   CpuProfilingStatus StartProfiling(
       Local<String> title, CpuProfilingMode mode, bool record_samples = false,
       unsigned max_samples = CpuProfilingOptions::kNoSampleLimit);
 
   /**
    * The same as StartProfiling above, but the CpuProfilingMode defaults to
    * kLeafNodeLineNumbers mode, which was the previous default behavior of the
    * profiler.
    */
   CpuProfilingStatus StartProfiling(Local<String> title,
                                     bool record_samples = false);
 
   /**
    * Stops collecting CPU profile with a given id and returns it.
    */
   CpuProfile* Stop(ProfilerId id);
 
   /**
    * Stops collecting CPU profile with a given title and returns it.
    * If the title given is empty, finishes the last profile started.
    */
   CpuProfile* StopProfiling(Local<String> title);
 
   /**
    * Generate more detailed source positions to code objects. This results in
    * better results when mapping profiling samples to script source.
    */
   static void UseDetailedSourcePositionsForProfiling(Isolate* isolate);
 
  private:
   CpuProfiler();
   ~CpuProfiler();
   CpuProfiler(const CpuProfiler&);
   CpuProfiler& operator=(const CpuProfiler&);
 };
 
 /**
  * HeapSnapshotEdge represents a directed connection between heap
  * graph nodes: from retainers to retained nodes.
  */
 class V8_EXPORT HeapGraphEdge {
  public:
   enum Type {
     kContextVariable = 0,  // A variable from a function context.
     kElement = 1,          // An element of an array.
     kProperty = 2,         // A named object property.
     kInternal = 3,         // A link that can't be accessed from JS,
                            // thus, its name isn't a real property name
                            // (e.g. parts of a ConsString).
     kHidden = 4,           // A link that is needed for proper sizes
                            // calculation, but may be hidden from user.
     kShortcut = 5,         // A link that must not be followed during
                            // sizes calculation.
     kWeak = 6              // A weak reference (ignored by the GC).
   };
 
   /** Returns edge type (see HeapGraphEdge::Type). */
   Type GetType() const;
 
   /**
    * Returns edge name. This can be a variable name, an element index, or
    * a property name.
    */
   Local<Value> GetName() const;
 
   /** Returns origin node. */
   const HeapGraphNode* GetFromNode() const;
 
   /** Returns destination node. */
   const HeapGraphNode* GetToNode() const;
 };
 
 
 /**
  * HeapGraphNode represents a node in a heap graph.
  */
 class V8_EXPORT HeapGraphNode {
  public:
   enum Type {
     kHidden = 0,         // Hidden node, may be filtered when shown to user.
     kArray = 1,          // An array of elements.
     kString = 2,         // A string.
     kObject = 3,         // A JS object (except for arrays and strings).
     kCode = 4,           // Compiled code.
     kClosure = 5,        // Function closure.
     kRegExp = 6,         // RegExp.
     kHeapNumber = 7,     // Number stored in the heap.
     kNative = 8,         // Native object (not from V8 heap).
     kSynthetic = 9,      // Synthetic object, usually used for grouping
                          // snapshot items together.
     kConsString = 10,    // Concatenated string. A pair of pointers to strings.
     kSlicedString = 11,  // Sliced string. A fragment of another string.
     kSymbol = 12,        // A Symbol (ES6).
     kBigInt = 13,        // BigInt.
     kObjectShape = 14,   // Internal data used for tracking the shapes (or
                          // "hidden classes") of JS objects.
   };
 
   /** Returns node type (see HeapGraphNode::Type). */
   Type GetType() const;
 
   /**
    * Returns node name. Depending on node's type this can be the name
    * of the constructor (for objects), the name of the function (for
    * closures), string value, or an empty string (for compiled code).
    */
   Local<String> GetName() const;
 
   /**
    * Returns node id. For the same heap object, the id remains the same
    * across all snapshots.
    */
   SnapshotObjectId GetId() const;
 
   /** Returns node's own size, in bytes. */
   size_t GetShallowSize() const;
 
   /** Returns child nodes count of the node. */
   int GetChildrenCount() const;
 
   /** Retrieves a child by index. */
   const HeapGraphEdge* GetChild(int index) const;
 };
 
 /**
  * HeapSnapshots record the state of the JS heap at some moment.
  */
 class V8_EXPORT HeapSnapshot {
  public:
   enum SerializationFormat {
     kJSON = 0  // See format description near 'Serialize' method.
   };
 
   /** Returns the root node of the heap graph. */
   const HeapGraphNode* GetRoot() const;
 
   /** Returns a node by its id. */
   const HeapGraphNode* GetNodeById(SnapshotObjectId id) const;
 
   /** Returns total nodes count in the snapshot. */
   int GetNodesCount() const;
 
   /** Returns a node by index. */
   const HeapGraphNode* GetNode(int index) const;
 
   /** Returns a max seen JS object Id. */
   SnapshotObjectId GetMaxSnapshotJSObjectId() const;
 
   /**
    * Deletes the snapshot and removes it from HeapProfiler's list.
    * All pointers to nodes, edges and paths previously returned become
    * invalid.
    */
   void Delete();
 
   /**
    * Prepare a serialized representation of the snapshot. The result
    * is written into the stream provided in chunks of specified size.
    * The total length of the serialized snapshot is unknown in
    * advance, it can be roughly equal to JS heap size (that means,
    * it can be really big - tens of megabytes).
    *
    * For the JSON format, heap contents are represented as an object
    * with the following structure:
    *
    *  {
    *    snapshot: {
    *      title: "...",
    *      uid: nnn,
    *      meta: { meta-info },
    *      node_count: nnn,
    *      edge_count: nnn
    *    },
    *    nodes: [nodes array],
    *    edges: [edges array],
    *    strings: [strings array]
    *  }
    *
    * Nodes reference strings, other nodes, and edges by their indexes
    * in corresponding arrays.
    */
   void Serialize(OutputStream* stream,
                  SerializationFormat format = kJSON) const;
 };
 
 
 /**
  * An interface for reporting progress and controlling long-running
  * activities.
  */
 class V8_EXPORT ActivityControl {
  public:
   enum ControlOption {
     kContinue = 0,
     kAbort = 1
   };
   virtual ~ActivityControl() = default;
   /**
    * Notify about current progress. The activity can be stopped by
    * returning kAbort as the callback result.
    */
   virtual ControlOption ReportProgressValue(uint32_t done, uint32_t total) = 0;
 };
 
 /**
  * AllocationProfile is a sampled profile of allocations done by the program.
  * This is structured as a call-graph.
  */
 class V8_EXPORT AllocationProfile {
  public:
   struct Allocation {
     /**
      * Size of the sampled allocation object.
      */
     size_t size;
 
     /**
      * The number of objects of such size that were sampled.
      */
     unsigned int count;
   };
 
   /**
    * Represents a node in the call-graph.
    */
   struct Node {
     /**
      * Name of the function. May be empty for anonymous functions or if the
      * script corresponding to this function has been unloaded.
      */
     Local<String> name;
 
     /**
      * Name of the script containing the function. May be empty if the script
      * name is not available, or if the script has been unloaded.
      */
     Local<String> script_name;
 
     /**
      * id of the script where the function is located. May be equal to
      * v8::UnboundScript::kNoScriptId in cases where the script doesn't exist.
      */
     int script_id;
 
     /**
      * Start position of the function in the script.
      */
     int start_position;
 
     /**
      * 1-indexed line number where the function starts. May be
      * kNoLineNumberInfo if no line number information is available.
      */
     int line_number;
 
     /**
      * 1-indexed column number where the function starts. May be
      * kNoColumnNumberInfo if no line number information is available.
      */
     int column_number;
 
     /**
      * Unique id of the node.
      */
     uint32_t node_id;
 
     /**
      * List of callees called from this node for which we have sampled
      * allocations. The lifetime of the children is scoped to the containing
      * AllocationProfile.
      */
     std::vector<Node*> children;
 
     /**
      * List of self allocations done by this node in the call-graph.
      */
     std::vector<Allocation> allocations;
   };
 
   /**
    * Represent a single sample recorded for an allocation.
    */
   struct Sample {
     /**
      * id of the node in the profile tree.
      */
     uint32_t node_id;
 
     /**
      * Size of the sampled allocation object.
      */
     size_t size;
 
     /**
      * The number of objects of such size that were sampled.
      */
     unsigned int count;
 
     /**
      * Unique time-ordered id of the allocation sample. Can be used to track
      * what samples were added or removed between two snapshots.
      */
     uint64_t sample_id;
 
     /**
      * Indicates whether the sampled allocation is still live or has already
      * been collected by GC.
      */
     bool is_live;
   };
 
   /**
    * Returns the root node of the call-graph. The root node corresponds to an
    * empty JS call-stack. The lifetime of the returned Node* is scoped to the
    * containing AllocationProfile.
    */
   virtual Node* GetRootNode() = 0;
   virtual const std::vector<Sample>& GetSamples() = 0;
 
   virtual ~AllocationProfile() = default;
 
   static const int kNoLineNumberInfo = Message::kNoLineNumberInfo;
   static const int kNoColumnNumberInfo = Message::kNoColumnInfo;
 };
 
 /**
  * An object graph consisting of embedder objects and V8 objects.
  * Edges of the graph are strong references between the objects.
  * The embedder can build this graph during heap snapshot generation
  * to include the embedder objects in the heap snapshot.
  * Usage:
  * 1) Define derived class of EmbedderGraph::Node for embedder objects.
  * 2) Set the build embedder graph callback on the heap profiler using
  *    HeapProfiler::AddBuildEmbedderGraphCallback.
  * 3) In the callback use graph->AddEdge(node1, node2) to add an edge from
  *    node1 to node2.
  * 4) To represent references from/to V8 object, construct V8 nodes using
  *    graph->V8Node(value).
  */
 class V8_EXPORT EmbedderGraph {
  public:
   class Node {
    public:
     /**
      * Detachedness specifies whether an object is attached or detached from the
      * main application state. While unkown in general, there may be objects
      * that specifically know their state. V8 passes this information along in
      * the snapshot. Users of the snapshot may use it to annotate the object
      * graph.
      */
     enum class Detachedness : uint8_t {
       kUnknown = 0,
       kAttached = 1,
       kDetached = 2,
     };
 
     Node() = default;
     virtual ~Node() = default;
     virtual const char* Name() = 0;
     virtual size_t SizeInBytes() = 0;
     /**
      * The corresponding V8 wrapper node if not null.
      * During heap snapshot generation the embedder node and the V8 wrapper
      * node will be merged into one node to simplify retaining paths.
      */
     virtual Node* WrapperNode() { return nullptr; }
     virtual bool IsRootNode() { return false; }
     /** Must return true for non-V8 nodes. */
     virtual bool IsEmbedderNode() { return true; }
     /**
      * Optional name prefix. It is used in Chrome for tagging detached nodes.
      */
     virtual const char* NamePrefix() { return nullptr; }
 
     /**
      * Returns the NativeObject that can be used for querying the
      * |HeapSnapshot|.
      */
     virtual NativeObject GetNativeObject() { return nullptr; }
 
     /**
      * Detachedness state of a given object. While unkown in general, there may
      * be objects that specifically know their state. V8 passes this information
      * along in the snapshot. Users of the snapshot may use it to annotate the
      * object graph.
      */
     virtual Detachedness GetDetachedness() { return Detachedness::kUnknown; }
 
     /**
      * Returns the address of the object in the embedder heap, or nullptr to not
      * specify the address. If this address is provided, then V8 can generate
      * consistent IDs for objects across subsequent heap snapshots, which allows
      * devtools to determine which objects were retained from one snapshot to
      * the next. This value is used only if GetNativeObject returns nullptr.
      */
     virtual const void* GetAddress() { return nullptr; }
 
     Node(const Node&) = delete;
     Node& operator=(const Node&) = delete;
   };
 
   /**
    * Returns a node corresponding to the given V8 value. Ownership is not
    * transferred. The result pointer is valid while the graph is alive.
    *
    * For now the variant that takes v8::Data is not marked as abstract for
    * compatibility, but embedders who subclass EmbedderGraph are expected to
    * implement it. Then in the implementation of the variant that takes
    * v8::Value, they can simply forward the call to the one that takes
    * v8::Local<v8::Data>.
    */
   virtual Node* V8Node(const v8::Local<v8::Value>& value) = 0;
 
   /**
    * Returns a node corresponding to the given V8 value. Ownership is not
    * transferred. The result pointer is valid while the graph is alive.
    *
    * For API compatibility, this default implementation just checks that the
    * data is a v8::Value and forward it to the variant that takes v8::Value,
    * which is currently required to be implemented. In the future we'll remove
    * the v8::Value variant, and make this variant that takes v8::Data abstract
    * instead. If the embedder subclasses v8::EmbedderGraph and also use
    * v8::TracedReference<v8::Data>, they must override this variant.
    */
   virtual Node* V8Node(const v8::Local<v8::Data>& value);
 
   /**
    * Adds the given node to the graph and takes ownership of the node.
    * Returns a raw pointer to the node that is valid while the graph is alive.
    */
   virtual Node* AddNode(std::unique_ptr<Node> node) = 0;
 
   /**
    * Adds an edge that represents a strong reference from the given
    * node |from| to the given node |to|. The nodes must be added to the graph
    * before calling this function.
    *
    * If name is nullptr, the edge will have auto-increment indexes, otherwise
    * it will be named accordingly.
    */
   virtual void AddEdge(Node* from, Node* to, const char* name = nullptr) = 0;
 
   /**
    * Adds a count of bytes that are not associated with any particular Node.
    * An embedder may use this to represent the size of nodes which were omitted
    * from this EmbedderGraph despite being retained by the graph, or other
    * overhead costs. This number will contribute to the total size in a heap
    * snapshot, without being represented in the object graph.
    */
   virtual void AddNativeSize(size_t size) {}
 
   virtual ~EmbedderGraph() = default;
 };
 
 class QueryObjectPredicate {
  public:
   virtual ~QueryObjectPredicate() = default;
   virtual bool Filter(v8::Local<v8::Object> object) = 0;
 };
 
 /**
  * Interface for controlling heap profiling. Instance of the
  * profiler can be retrieved using v8::Isolate::GetHeapProfiler.
  */
 class V8_EXPORT HeapProfiler {
  public:
   void QueryObjects(v8::Local<v8::Context> context,
                     QueryObjectPredicate* predicate,
                     std::vector<v8::Global<v8::Object>>* objects);
 
   enum SamplingFlags {
     kSamplingNoFlags = 0,
     kSamplingForceGC = 1 << 0,
     kSamplingIncludeObjectsCollectedByMajorGC = 1 << 1,
     kSamplingIncludeObjectsCollectedByMinorGC = 1 << 2,
   };
 
   /**
    * Callback function invoked during heap snapshot generation to retrieve
    * the embedder object graph. The callback should use graph->AddEdge(..) to
    * add references between the objects.
    * The callback must not trigger garbage collection in V8.
    */
   typedef void (*BuildEmbedderGraphCallback)(v8::Isolate* isolate,
                                              v8::EmbedderGraph* graph,
                                              void* data);
 
   /**
    * Callback function invoked during heap snapshot generation to retrieve
    * the detachedness state of a JS object referenced by a TracedReference.
    *
    * The callback takes Local<Value> as parameter to allow the embedder to
    * unpack the TracedReference into a Local and reuse that Local for different
    * purposes.
    */
   using GetDetachednessCallback = EmbedderGraph::Node::Detachedness (*)(
       v8::Isolate* isolate, const v8::Local<v8::Value>& v8_value,
       uint16_t class_id, void* data);
 
   /** Returns the number of snapshots taken. */
   int GetSnapshotCount();
 
   /** Returns a snapshot by index. */
   const HeapSnapshot* GetHeapSnapshot(int index);
 
   /**
    * Returns SnapshotObjectId for a heap object referenced by |value| if
    * it has been seen by the heap profiler, kUnknownObjectId otherwise.
    */
   SnapshotObjectId GetObjectId(Local<Value> value);
 
   /**
    * Returns SnapshotObjectId for a native object referenced by |value| if it
    * has been seen by the heap profiler, kUnknownObjectId otherwise.
    */
   SnapshotObjectId GetObjectId(NativeObject value);
 
   /**
    * Returns heap object with given SnapshotObjectId if the object is alive,
    * otherwise empty handle is returned.
    */
   Local<Value> FindObjectById(SnapshotObjectId id);
 
   /**
    * Clears internal map from SnapshotObjectId to heap object. The new objects
    * will not be added into it unless a heap snapshot is taken or heap object
    * tracking is kicked off.
    */
   void ClearObjectIds();
 
   /**
    * A constant for invalid SnapshotObjectId. GetSnapshotObjectId will return
    * it in case heap profiler cannot find id  for the object passed as
    * parameter. HeapSnapshot::GetNodeById will always return NULL for such id.
    */
   static const SnapshotObjectId kUnknownObjectId = 0;
 
   /**
    * Callback interface for retrieving user friendly names of global objects.
    *
    * This interface will soon be deprecated in favour of ContextNameResolver.
    */
   class ObjectNameResolver {
    public:
     /**
      * Returns name to be used in the heap snapshot for given node. Returned
      * string must stay alive until snapshot collection is completed.
      */
     virtual const char* GetName(Local<Object> object) = 0;
 
    protected:
     virtual ~ObjectNameResolver() = default;
   };
 
   /**
    * Callback interface for retrieving user friendly names of a V8::Context
    * objects.
    */
   class ContextNameResolver {
    public:
     /**
      * Returns name to be used in the heap snapshot for given node. Returned
      * string must stay alive until snapshot collection is completed.
      * If no user friendly name is available return nullptr.
      */
     virtual const char* GetName(Local<Context> context) = 0;
 
    protected:
     virtual ~ContextNameResolver() = default;
   };
 
   enum class HeapSnapshotMode {
     /**
      * Heap snapshot for regular developers.
      */
     kRegular,
     /**
      * Heap snapshot is exposing internals that may be useful for experts.
      */
     kExposeInternals,
   };
 
   enum class NumericsMode {
     /**
      * Numeric values are hidden as they are values of the corresponding
      * objects.
      */
     kHideNumericValues,
     /**
      * Numeric values are exposed in artificial fields.
      */
     kExposeNumericValues
   };
 
   struct HeapSnapshotOptions final {
     // Manually define default constructor here to be able to use it in
     // `TakeSnapshot()` below.
     // NOLINTNEXTLINE
     HeapSnapshotOptions() {}
 
     // TODO(https://crbug.com/333672197): remove once ObjectNameResolver is
     // removed.
     ALLOW_COPY_AND_MOVE_WITH_DEPRECATED_FIELDS(HeapSnapshotOptions)
 
     /**
      * The control used to report intermediate progress to.
      */
     ActivityControl* control = nullptr;
     /**
      * The resolver used by the snapshot generator to get names for V8 objects.
      */
     V8_DEPRECATED("Use context_name_resolver callback instead.")
     ObjectNameResolver* global_object_name_resolver = nullptr;
     /**
      * The resolver used by the snapshot generator to get names for v8::Context
      * objects.
      * In case both this and |global_object_name_resolver| callbacks are
      * provided, this one will be used.
      */
     ContextNameResolver* context_name_resolver = nullptr;
     /**
      * Mode for taking the snapshot, see `HeapSnapshotMode`.
      */
     HeapSnapshotMode snapshot_mode = HeapSnapshotMode::kRegular;
     /**
      * Mode for dealing with numeric values, see `NumericsMode`.
      */
     NumericsMode numerics_mode = NumericsMode::kHideNumericValues;
     /**
      * Whether stack is considered as a root set.
      */
     cppgc::EmbedderStackState stack_state =
         cppgc::EmbedderStackState::kMayContainHeapPointers;
   };
 
   /**
    * Takes a heap snapshot.
    *
    * \returns the snapshot.
    */
   const HeapSnapshot* TakeHeapSnapshot(
       const HeapSnapshotOptions& options = HeapSnapshotOptions());
 
   /**
    * Takes a heap snapshot. See `HeapSnapshotOptions` for details on the
    * parameters.
    *
    * \returns the snapshot.
    */
   V8_DEPRECATED("Use overload with ContextNameResolver* resolver instead.")
   const HeapSnapshot* TakeHeapSnapshot(
       ActivityControl* control, ObjectNameResolver* global_object_name_resolver,
       bool hide_internals = true, bool capture_numeric_value = false);
   const HeapSnapshot* TakeHeapSnapshot(ActivityControl* control,
                                        ContextNameResolver* resolver,
                                        bool hide_internals = true,
                                        bool capture_numeric_value = false);
   // TODO(333672197): remove this version once ObjectNameResolver* overload
   // is removed.
   const HeapSnapshot* TakeHeapSnapshot(ActivityControl* control,
                                        std::nullptr_t resolver = nullptr,
                                        bool hide_internals = true,
                                        bool capture_numeric_value = false);
 
   /**
    * Obtains list of Detached JS Wrapper Objects. This functon calls garbage
    * collection, then iterates over traced handles in the isolate
    */
   std::vector<v8::Local<v8::Value>> GetDetachedJSWrapperObjects();
 
   /**
    * Starts tracking of heap objects population statistics. After calling
    * this method, all heap objects relocations done by the garbage collector
    * are being registered.
    *
    * |track_allocations| parameter controls whether stack trace of each
    * allocation in the heap will be recorded and reported as part of
    * HeapSnapshot.
    */
   void StartTrackingHeapObjects(bool track_allocations = false);
 
   /**
    * Adds a new time interval entry to the aggregated statistics array. The
    * time interval entry contains information on the current heap objects
    * population size. The method also updates aggregated statistics and
    * reports updates for all previous time intervals via the OutputStream
    * object. Updates on each time interval are provided as a stream of the
    * HeapStatsUpdate structure instances.
    * If |timestamp_us| is supplied, timestamp of the new entry will be written
    * into it. The return value of the function is the last seen heap object Id.
    *
    * StartTrackingHeapObjects must be called before the first call to this
    * method.
    */
   SnapshotObjectId GetHeapStats(OutputStream* stream,
                                 int64_t* timestamp_us = nullptr);
 
   /**
    * Stops tracking of heap objects population statistics, cleans up all
    * collected data. StartHeapObjectsTracking must be called again prior to
    * calling GetHeapStats next time.
    */
   void StopTrackingHeapObjects();
 
   /**
    * Starts gathering a sampling heap profile. A sampling heap profile is
    * similar to tcmalloc's heap profiler and Go's mprof. It samples object
    * allocations and builds an online 'sampling' heap profile. At any point in
    * time, this profile is expected to be a representative sample of objects
    * currently live in the system. Each sampled allocation includes the stack
    * trace at the time of allocation, which makes this really useful for memory
    * leak detection.
    *
    * This mechanism is intended to be cheap enough that it can be used in
    * production with minimal performance overhead.
    *
    * Allocations are sampled using a randomized Poisson process. On average, one
    * allocation will be sampled every |sample_interval| bytes allocated. The
    * |stack_depth| parameter controls the maximum number of stack frames to be
    * captured on each allocation.
    *
    * NOTE: Support for native allocations doesn't exist yet, but is anticipated
    * in the future.
    *
    * Objects allocated before the sampling is started will not be included in
    * the profile.
    *
    * Returns false if a sampling heap profiler is already running.
    */
   bool StartSamplingHeapProfiler(uint64_t sample_interval = 512 * 1024,
                                  int stack_depth = 16,
                                  SamplingFlags flags = kSamplingNoFlags);
 
   /**
    * Stops the sampling heap profile and discards the current profile.
    */
   void StopSamplingHeapProfiler();
 
   /**
    * Returns the sampled profile of allocations allocated (and still live) since
    * StartSamplingHeapProfiler was called. The ownership of the pointer is
    * transferred to the caller. Returns nullptr if sampling heap profiler is not
    * active.
    */
   AllocationProfile* GetAllocationProfile();
 
   /**
    * Deletes all snapshots taken. All previously returned pointers to
    * snapshots and their contents become invalid after this call.
    */
   void DeleteAllHeapSnapshots();
 
   void AddBuildEmbedderGraphCallback(BuildEmbedderGraphCallback callback,
                                      void* data);
   void RemoveBuildEmbedderGraphCallback(BuildEmbedderGraphCallback callback,
                                         void* data);
 
   void SetGetDetachednessCallback(GetDetachednessCallback callback, void* data);
 
   /**
    * Returns whether the heap profiler is currently taking a snapshot.
    */
   bool IsTakingSnapshot();
 
   /**
    * Allocates a copy of the provided string within the heap snapshot generator
    * and returns a pointer to the copy. May only be called during heap snapshot
    * generation.
    */
   const char* CopyNameForHeapSnapshot(const char* name);
 
   /**
    * Default value of persistent handle class ID. Must not be used to
    * define a class. Can be used to reset a class of a persistent
    * handle.
    */
   static const uint16_t kPersistentHandleNoClassId = 0;
 
  private:
   HeapProfiler();
   ~HeapProfiler();
   HeapProfiler(const HeapProfiler&);
   HeapProfiler& operator=(const HeapProfiler&);
 };
 
 /**
  * A struct for exporting HeapStats data from V8, using "push" model.
  * See HeapProfiler::GetHeapStats.
  */
 struct HeapStatsUpdate {
   HeapStatsUpdate(uint32_t index, uint32_t count, uint32_t size)
     : index(index), count(count), size(size) { }
   uint32_t index;  // Index of the time interval that was changed.
   uint32_t count;  // New value of count field for the interval with this index.
   uint32_t size;  // New value of size field for the interval with this index.
 };
 
 #define CODE_EVENTS_LIST(V)                          \
   V(Builtin)                                         \
   V(Callback)                                        \
   V(Eval)                                            \
   V(Function)                                        \
   V(InterpretedFunction)                             \
   V(Handler)                                         \
   V(BytecodeHandler)                                 \
   V(LazyCompile) /* Unused, use kFunction instead */ \
   V(RegExp)                                          \
   V(Script)                                          \
   V(Stub)                                            \
   V(Relocation)
 
 /**
  * Note that this enum may be extended in the future. Please include a default
  * case if this enum is used in a switch statement.
  */
 enum CodeEventType {
   kUnknownType = 0
 #define V(Name) , k##Name##Type
   CODE_EVENTS_LIST(V)
 #undef V
 };
 
 /**
  * Representation of a code creation event
  */
 class V8_EXPORT CodeEvent {
  public:
   uintptr_t GetCodeStartAddress();
   size_t GetCodeSize();
   Local<String> GetFunctionName();
   Local<String> GetScriptName();
   int GetScriptLine();
   int GetScriptColumn();
   /**
    * NOTE (mmarchini): We can't allocate objects in the heap when we collect
    * existing code, and both the code type and the comment are not stored in the
    * heap, so we return those as const char*.
    */
   CodeEventType GetCodeType();
   const char* GetComment();
 
   static const char* GetCodeEventTypeName(CodeEventType code_event_type);
 
   uintptr_t GetPreviousCodeStartAddress();
 };
 
 /**
  * Interface to listen to code creation and code relocation events.
  */
 class V8_EXPORT CodeEventHandler {
  public:
   /**
    * Creates a new listener for the |isolate|. The isolate must be initialized.
    * The listener object must be disposed after use by calling |Dispose| method.
    * Multiple listeners can be created for the same isolate.
    */
   explicit CodeEventHandler(Isolate* isolate);
   virtual ~CodeEventHandler();
 
   /**
    * Handle is called every time a code object is created or moved. Information
    * about each code event will be available through the `code_event`
    * parameter.
    *
    * When the CodeEventType is kRelocationType, the code for this CodeEvent has
    * moved from `GetPreviousCodeStartAddress()` to `GetCodeStartAddress()`.
    */
   virtual void Handle(CodeEvent* code_event) = 0;
 
   /**
    * Call `Enable()` to starts listening to code creation and code relocation
    * events. These events will be handled by `Handle()`.
    */
   void Enable();
 
   /**
    * Call `Disable()` to stop listening to code creation and code relocation
    * events.
    */
   void Disable();
 
  private:
   CodeEventHandler();
   CodeEventHandler(const CodeEventHandler&);
   CodeEventHandler& operator=(const CodeEventHandler&);
   void* internal_listener_;
 };
 
 }  // namespace v8
 
 
 #endif  // V8_V8_PROFILER_H_

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