/* 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 debugger_ExecutionTracer_h
#define debugger_ExecutionTracer_h

#include "mozilla/Assertions.h"         // MOZ_DIAGNOSTIC_ASSERT, MOZ_ASSERT
#include "mozilla/BaseProfilerUtils.h"  // profiler_current_thread_id
#include "mozilla/EndianUtils.h"        // NativeEndian
#include "mozilla/Maybe.h"  // mozilla::Maybe, mozilla::Some, mozilla::Nothing
#include "mozilla/Span.h"
#include "mozilla/TimeStamp.h"

#include <bit>       // std::has_single_bit
#include <limits>    // std::numeric_limits
#include <stddef.h>  // size_t
#include <stdint.h>  // uint8_t, uint16_t

#include "js/CharacterEncoding.h"  // JS::UTF8Chars
#include "js/Debug.h"              // JS::ExecutionTrace
#include "js/RootingAPI.h"         // JS::Rooted
#include "js/Utility.h"            // js_malloc, js_free
#include "js/Value.h"              // JS::Value
#include "vm/ErrorObject.h"        // ErrorObject
#include "vm/JSContext.h"          // JSContext
#include "vm/Stack.h"              // js::AbstractFramePtr

namespace js {

enum class OutOfLineEntryType : uint8_t {
  ScriptURL,
  Atom,
  Shape,
};

enum class InlineEntryType : uint8_t {
  StackFunctionEnter,
  StackFunctionLeave,
  LabelEnter,
  LabelLeave,
  Error,
};

enum class PropertyKeyKind : uint8_t {
  Undefined,
  String,
  Int,
  Symbol,
};

using TracingScratchBuffer = mozilla::Vector<char, 512>;

// TODO: it should be noted that part of this design is informed by the fact
// that it evolved from a prototype which wrote this data from a content
// process and read it from the parent process, allowing the parent process to
// display the trace in real time as the program executes. Bug 1910182 tracks
// the next steps for making that prototype a reality.
template <size_t BUFFER_SIZE>
class TracingBuffer {
  static_assert(std::has_single_bit(BUFFER_SIZE));

  // BUFFER_SIZE is the size of the underlying ring buffer, and BUFFER_MASK
  // masks off indices into it in order to wrap around
  static const size_t BUFFER_MASK = BUFFER_SIZE - 1;

  // The entry header is just a u16 that holds the size of the entry in bytes.
  // This is used for asserting the integrity of the data as well as for
  // skipping the read head forward if it's going to be overwritten by the
  // write head
  static const size_t ENTRY_HEADER_SIZE = sizeof(uint16_t);

  // The underlying ring buffer
  uint8_t* buffer_ = nullptr;

  // NOTE: The following u64s are unwrapped indices into the ring buffer, so
  // they must always be masked off with BUFFER_MASK before using them to
  // access buffer_:

  // Represents how much has been written into the ring buffer and is ready
  // for reading
  uint64_t writeHead_ = 0;

  // Represents how much has been read from the ring buffer
  uint64_t readHead_ = 0;

  // When not equal to writeHead_, this represents unfinished write progress
  // into the buffer. After each entry successfully finished writing,
  // writeHead_ is set to this value
  uint64_t uncommittedWriteHead_ = 0;

  // Similar to uncommittedWriteHead_, but for the purposes of reading
  uint64_t uncommittedReadHead_ = 0;

  bool ensureScratchBufferSize(TracingScratchBuffer& scratchBuffer,
                               size_t requiredSize) {
    if (scratchBuffer.length() >= requiredSize) {
      return true;
    }
    return scratchBuffer.growByUninitialized(requiredSize -
                                             scratchBuffer.length());
  }

 public:
  static const size_t SIZE = BUFFER_SIZE;

  ~TracingBuffer() {
    if (buffer_) {
      js_free(buffer_);
    }
  }

  bool init() {
    buffer_ = static_cast<uint8_t*>(js_malloc(BUFFER_SIZE));
    return buffer_ != nullptr;
  }

  bool readable() { return writeHead_ > readHead_; }

  uint64_t uncommittedWriteHead() { return uncommittedWriteHead_; }

  uint64_t readHead() { return readHead_; }

  void beginWritingEntry() {
    // uncommittedWriteHead_ can be > writeHead_ if a previous write failed.
    // In that case, this effectively discards whatever was written during that
    // time
    MOZ_ASSERT(uncommittedWriteHead_ >= writeHead_);
    uncommittedWriteHead_ = writeHead_;
    uncommittedWriteHead_ += ENTRY_HEADER_SIZE;
  }

  void finishWritingEntry() {
    MOZ_RELEASE_ASSERT(uncommittedWriteHead_ - writeHead_ <=
                       std::numeric_limits<uint16_t>::max());
    uint16_t entryHeader = uint16_t(uncommittedWriteHead_ - writeHead_);
    writeAtOffset(entryHeader, writeHead_);
    writeHead_ = uncommittedWriteHead_;
  }

  void beginReadingEntry() {
    MOZ_ASSERT(uncommittedReadHead_ == readHead_);
    // We will read the entry header (still pointed to by readHead_) from
    // inside finishReadingEntry
    uncommittedReadHead_ += ENTRY_HEADER_SIZE;
  }

  void finishReadingEntry() {
    uint16_t entryHeader;
    readAtOffset(&entryHeader, readHead_);
    size_t read = uncommittedReadHead_ - readHead_;

    MOZ_RELEASE_ASSERT(entryHeader == uint16_t(read));
    readHead_ += entryHeader;
    uncommittedReadHead_ = readHead_;
  }

  void skipEntry() {
    uint16_t entryHeader;
    readAtOffset(&entryHeader, readHead_);
    readHead_ += entryHeader;
    uncommittedReadHead_ = readHead_;
  }

  void writeBytesAtOffset(const uint8_t* bytes, size_t length,
                          uint64_t offset) {
    MOZ_ASSERT(offset + length <= readHead_ + BUFFER_SIZE);

    size_t maskedWriteHead = offset & BUFFER_MASK;
    if (maskedWriteHead + length > BUFFER_SIZE) {
      size_t firstChunk = BUFFER_SIZE - maskedWriteHead;
      memcpy(buffer_ + maskedWriteHead, bytes, firstChunk);
      memcpy(buffer_, bytes + firstChunk, length - firstChunk);
    } else {
      memcpy(buffer_ + maskedWriteHead, bytes, length);
    }
  }

  void writeBytes(const uint8_t* bytes, size_t length) {
    // Skip the read head forward if we're about to overwrite unread entries
    while (MOZ_UNLIKELY(uncommittedWriteHead_ + length >
                        readHead_ + BUFFER_SIZE)) {
      skipEntry();
    }

    writeBytesAtOffset(bytes, length, uncommittedWriteHead_);
    uncommittedWriteHead_ += length;
  }

  template <typename T>
  void write(T val) {
    // No magic hidden work allowed here - we are just reducing duplicate code
    // serializing integers and floats.
    static_assert(std::is_arithmetic_v<T>);
    if constexpr (sizeof(T) > 1) {
      val = mozilla::NativeEndian::swapToLittleEndian(val);
    }

    writeBytes(reinterpret_cast<const uint8_t*>(&val), sizeof(T));
  }

  template <typename T>
  void writeAtOffset(T val, uint64_t offset) {
    static_assert(std::is_arithmetic_v<T>);
    if constexpr (sizeof(T) > 1) {
      val = mozilla::NativeEndian::swapToLittleEndian(val);
    }

    writeBytesAtOffset(reinterpret_cast<const uint8_t*>(&val), sizeof(T),
                       offset);
  }

  void writeEmptyString() {
    write(uint8_t(JS::TracerStringEncoding::Latin1));
    write(uint32_t(0));  // length
  }

  void writeEmptySmallString() { write(uint16_t(0)); }

  enum class InlineStringEncoding { No, Yes };

  // Helper for writing the length and encoding, which are sometimes squished
  // into one value
  template <typename LengthType = uint32_t,
            InlineStringEncoding InlineEncoding = InlineStringEncoding::No>
  void writeAdjustedLengthAndEncoding(
      size_t* length, JS::TracerStringEncoding encoding,
      size_t lengthLimit = std::numeric_limits<LengthType>::max()) {
    if (*length > lengthLimit) {
      *length = lengthLimit;
    }

    if constexpr (InlineEncoding == InlineStringEncoding::No) {
      write(uint8_t(encoding));
      write(LengthType(*length));
    } else {
      constexpr LengthType encodingBits = 2;
      LengthType typedLength =
          LengthType(*length) |
          (uint16_t(encoding) << (sizeof(LengthType) * 8 - encodingBits));
      write(typedLength);
    }
  }

  template <typename LengthType = uint32_t,
            InlineStringEncoding InlineEncoding = InlineStringEncoding::No>
  bool writeString(
      JSContext* cx, JS::Handle<JSString*> str,
      size_t lengthLimit = std::numeric_limits<LengthType>::max()) {
    JS::TracerStringEncoding encoding;
    if (str->hasLatin1Chars()) {
      encoding = JS::TracerStringEncoding::Latin1;
    } else {
      encoding = JS::TracerStringEncoding::TwoByte;
    }

    // TODO: if ropes are common we can certainly serialize them without
    // linearizing - this is just easy
    JSLinearString* linear = str->ensureLinear(cx);
    if (!linear) {
      return false;
    }

    size_t length = linear->length();
    writeAdjustedLengthAndEncoding<LengthType, InlineEncoding>(
        &length, encoding, lengthLimit);

    size_t size = length;
    JS::AutoAssertNoGC nogc;
    const uint8_t* charBuffer = nullptr;
    if (encoding == JS::TracerStringEncoding::TwoByte) {
      size *= sizeof(char16_t);
      charBuffer = reinterpret_cast<const uint8_t*>(linear->twoByteChars(nogc));
    } else {
      charBuffer = reinterpret_cast<const uint8_t*>(linear->latin1Chars(nogc));
    }
    writeBytes(charBuffer, size);
    return true;
  }

  template <typename CharType, JS::TracerStringEncoding Encoding,
            typename LengthType = uint32_t,
            InlineStringEncoding InlineEncoding = InlineStringEncoding::No>
  void writeCString(
      const CharType* chars,
      size_t lengthLimit = std::numeric_limits<LengthType>::max()) {
    size_t length = std::char_traits<CharType>::length(chars);
    static_assert(sizeof(CharType) == 1 ||
                  Encoding == JS::TracerStringEncoding::TwoByte);
    static_assert(sizeof(CharType) <= 2);

    writeAdjustedLengthAndEncoding<LengthType, InlineEncoding>(
        &length, Encoding, lengthLimit);

    const size_t size = length * sizeof(CharType);
    writeBytes(reinterpret_cast<const uint8_t*>(chars), size);
  }

  bool writeSmallString(JSContext* cx, JS::Handle<JSString*> str) {
    return writeString<uint16_t, InlineStringEncoding::Yes>(
        cx, str, JS::ValueSummary::SMALL_STRING_LENGTH_LIMIT);
  }

  template <typename CharType, JS::TracerStringEncoding Encoding>
  void writeSmallCString(const CharType* chars) {
    writeCString<CharType, Encoding, char16_t, InlineStringEncoding::Yes>(
        chars, JS::ValueSummary::SMALL_STRING_LENGTH_LIMIT);
  }

  void readBytesAtOffset(uint8_t* bytes, size_t length, uint64_t offset) {
    size_t maskedReadHead = offset & BUFFER_MASK;
    if (maskedReadHead + length > BUFFER_SIZE) {
      size_t firstChunk = BUFFER_SIZE - maskedReadHead;
      memcpy(bytes, buffer_ + maskedReadHead, firstChunk);
      memcpy(bytes + firstChunk, buffer_, length - firstChunk);
    } else {
      memcpy(bytes, buffer_ + maskedReadHead, length);
    }
  }

  void readBytes(uint8_t* bytes, size_t length) {
    readBytesAtOffset(bytes, length, uncommittedReadHead_);
    uncommittedReadHead_ += length;
  }

  template <typename T>
  void read(T* val) {
    static_assert(std::is_arithmetic_v<T>);

    readBytes(reinterpret_cast<uint8_t*>(val), sizeof(T));
    if constexpr (sizeof(T) > 1) {
      *val = mozilla::NativeEndian::swapFromLittleEndian(*val);
    }
  }

  template <typename T>
  void readAtOffset(T* val, uint64_t offset) {
    static_assert(std::is_arithmetic_v<T>);

    readBytesAtOffset(reinterpret_cast<uint8_t*>(val), sizeof(T), offset);
    if constexpr (sizeof(T) > 1) {
      *val = mozilla::NativeEndian::swapFromLittleEndian(*val);
    }
  }

  // Reads a string from our buffer into the stringBuffer. Converts everything
  // to null-terminated UTF-8
  template <typename LengthType = uint32_t,
            InlineStringEncoding InlineEncoding = InlineStringEncoding::No>
  bool readString(TracingScratchBuffer& scratchBuffer,
                  mozilla::Vector<char>& stringBuffer, size_t* index) {
    uint8_t encodingByte;
    LengthType length;
    if constexpr (InlineEncoding == InlineStringEncoding::Yes) {
      LengthType lengthAndEncoding;
      read(&lengthAndEncoding);
      constexpr LengthType encodingBits = 2;
      constexpr LengthType encodingShift =
          sizeof(LengthType) * 8 - encodingBits;
      constexpr LengthType encodingMask = 0b11 << encodingShift;
      length = lengthAndEncoding & ~encodingMask;
      encodingByte = (lengthAndEncoding & encodingMask) >> encodingShift;
    } else {
      read(&encodingByte);
      read(&length);
    }

    JS::TracerStringEncoding encoding = JS::TracerStringEncoding(encodingByte);

    *index = stringBuffer.length();

    if (length == 0) {
      if (!stringBuffer.append('\0')) {
        return false;
      }
      return true;
    }

    if (encoding == JS::TracerStringEncoding::UTF8) {
      size_t reserveLength = length + 1;
      if (!stringBuffer.growByUninitialized(reserveLength)) {
        return false;
      }
      char* writePtr = stringBuffer.end() - reserveLength;
      readBytes(reinterpret_cast<uint8_t*>(writePtr), length);
      writePtr[length] = '\0';
    } else if (encoding == JS::TracerStringEncoding::Latin1) {
      if (!ensureScratchBufferSize(scratchBuffer, length)) {
        return false;
      }
      readBytes(reinterpret_cast<uint8_t*>(scratchBuffer.begin()), length);

      // A single latin-1 code point maps to either 1 or 2 UTF-8 code units.
      // The + 1 is for the null terminator.
      size_t reserveLength = length * 2 + 1;
      if (!stringBuffer.reserve(stringBuffer.length() + reserveLength)) {
        return false;
      }
      char* writePtr = stringBuffer.end();

      size_t convertedLength = mozilla::ConvertLatin1toUtf8(
          mozilla::Span<const char>(scratchBuffer.begin(), length),
          mozilla::Span<char>(writePtr, reserveLength));
      writePtr[convertedLength] = 0;

      // We reserved above, which just grows the capacity but not the length.
      // This just commits the exact length increase.
      if (!stringBuffer.growByUninitialized(convertedLength + 1)) {
        return false;
      }
    } else {
      MOZ_ASSERT(encoding == JS::TracerStringEncoding::TwoByte);
      if (!ensureScratchBufferSize(scratchBuffer, length * sizeof(char16_t))) {
        return false;
      }
      readBytes(reinterpret_cast<uint8_t*>(scratchBuffer.begin()),
                length * sizeof(char16_t));

      // Non-surrogate-paired single UTF-16 code unit maps to 1 to 3 UTF-8
      // code units. Surrogate paired UTF-16 code units map to 4 to 6 UTF-8
      // code units.
      size_t reserveLength = length * 3 + 1;
      if (!stringBuffer.reserve(stringBuffer.length() + reserveLength)) {
        return false;
      }
      char* writePtr = stringBuffer.end();

      size_t convertedLength = mozilla::ConvertUtf16toUtf8(
          mozilla::Span<const char16_t>(
              reinterpret_cast<char16_t*>(scratchBuffer.begin()), length),
          mozilla::Span<char>(writePtr, reserveLength));
      writePtr[convertedLength] = 0;

      // We reserved above, which just grows the capacity but not the length.
      // This just commits the exact length increase.
      if (!stringBuffer.growByUninitialized(convertedLength + 1)) {
        return false;
      }
    }

    return true;
  }

  bool readSmallString(TracingScratchBuffer& scratchBuffer,
                       mozilla::Vector<char>& stringBuffer, size_t* index) {
    return readString<uint16_t, InlineStringEncoding::Yes>(scratchBuffer,
                                                           stringBuffer, index);
  }
};

// These sizes are to some degree picked out of a hat, and eventually it might
// be nice to make them configurable. For reference, I measured it costing
// 145MB to open gdocs and create an empty document, so 256MB is just some
// extra wiggle room for complex use cases.
using InlineDataBuffer = TracingBuffer<1 << 28>;

// We include a separate buffer for value summaries, so that we can store them
// contiguously and so we don't lose information from the inline data if a
// script has a lot of large values for instance.
using ValueDataBuffer = InlineDataBuffer;

// The size for the out of line data is much smaller, so I just picked a size
// that was much smaller but big enough that I didn't see us running out of it
// when playing around on various complex apps. Again, it would be great in the
// future for this to be configurable.
using OutOfLineDataBuffer = TracingBuffer<1 << 22>;

class ValueSummaries {
  ValueDataBuffer* valueData_ = nullptr;
  OutOfLineDataBuffer* outOfLineData_ = nullptr;

  friend struct ::JS_TracerSummaryWriter;

 public:
  // Sometimes we write ValueSummarys as nested properties of other
  // ValueSummarys. This enum is used to indicate that in code when necessary.
  // (This value is not written into the serialized format, and should instead
  // be tracked by the reader)
  enum class IsNested { No, Yes };

  void init(ValueDataBuffer* valueData, OutOfLineDataBuffer* outOfLineData) {
    valueData_ = valueData;
    outOfLineData_ = outOfLineData;
  }

  bool writeValue(JSContext* cx, JS::Handle<JS::Value> val, IsNested nested);

  // valueBufferIndex will hold the index at which we wrote the arguments into
  // the valueData_ buffer
  bool writeArguments(JSContext* cx, AbstractFramePtr frame,
                      uint64_t* valueBufferIndex);

  // Unrolls the underlying ring buffer into a contiguous, compacted buffer
  // and puts it into the context's valueBuffer field.
  bool populateOutputBuffer(JS::ExecutionTrace::TracedJSContext& context);

  // If ringBufferIndex is still valid, translates it into an index into the
  // output buffer. Otherwise, this returns
  // JS::ExecutionTrace::EXPIRED_VALUES_MAGIC.
  int32_t getOutputBufferIndex(uint64_t ringBufferIndex);

  void writeHeader(JS::ValueType type, uint8_t flags);
  bool writeShapeSummary(JSContext* cx, JS::Handle<NativeShape*> shape);

  // Only writes the class name
  bool writeMinimalShapeSummary(JSContext* cx, JS::Handle<Shape*> shape);

  void writeObjectHeader(JS::ObjectSummary::Kind kind, uint8_t flags);

  bool writeObject(JSContext* cx, JS::Handle<JSObject*> obj, IsNested nested);

  bool writeFunctionSummary(JSContext* cx, JS::Handle<JSFunction*> fn,
                            IsNested nested);
  bool writeArrayObjectSummary(JSContext* cx, JS::Handle<ArrayObject*> array,
                               IsNested nested);
  bool writeSetObjectSummary(JSContext* cx, JS::Handle<SetObject*> set,
                             IsNested nested);
  bool writeMapObjectSummary(JSContext* cx, JS::Handle<MapObject*> map,
                             IsNested nested);
  bool writeErrorObjectSummary(JSContext* cx, JS::Handle<JSObject*> obj,
                               JS::Handle<ErrorObject*> error, IsNested nested);
  bool writeGenericOrWrappedPrimitiveObjectSummary(
      JSContext* cx, JS::Handle<NativeObject*> nobj, IsNested nested);
  bool writeExternalObjectSummary(JSContext* cx, JS::Handle<NativeObject*> nobj,
                                  IsNested nested);

  bool writeStringLikeValue(JSContext* cx, JS::ValueType valueType,
                            JS::Handle<JSString*> str);
};

// An ExecutionTracer is responsible for recording JS execution while it is
// enabled to a set of ring buffers, and providing that information as a JS
// object when requested. See Debugger.md (collectNativeTrace) for more details.
class ExecutionTracer {
 private:
  // The fields below should only be accessed while we hold the lock.
  static Mutex globalInstanceLock MOZ_UNANNOTATED;
  static mozilla::Vector<ExecutionTracer*> globalInstances;

  // The buffers below should only be accessed while we hold the lock.
  Mutex bufferLock_ MOZ_UNANNOTATED;

  // This holds the actual entries, one for each push or pop of a frame or label
  InlineDataBuffer inlineData_;

  // This holds data that may be duplicated across entries, like script URLs or
  // function names. This should generally be much smaller in terms of raw
  // bytes. Note however that we can still wrap around this buffer and lose
  // entries - the system is best effort, and the consumer must accomodate the
  // fact that entries from inlineData_ may reference expired data from
  // outOfLineData_
  OutOfLineDataBuffer outOfLineData_;

  // This holds summaries of various values recorded during tracing. Currently
  // this only contains values for function arguments. TODO: Add support for
  // function return values.
  ValueDataBuffer valueData_;

  // This is just an ID that allows the profiler to easily correlate the trace
  // for a given context with the correct thread in the output profile.
  // We're operating on the assumption that there is one JSContext per thread,
  // which should be true enough for our uses in Firefox, but doesn't have to
  // be true everywhere.
  mozilla::baseprofiler::BaseProfilerThreadId threadId_;

  // This is a helper class for writing value data to the valueData_ and
  // outOfLineData_ buffers. It holds pointers to those two buffers and houses
  // all of the logic for writing the value summaries themselves.
  ValueSummaries valueSummaries_;

  // When we encounter an error during tracing, we write one final Error entry
  // and suspend tracing indefinitely. This allows the consumer to get some
  // information about what led up to the error, while preventing any
  // additional future overhead. An alternative to this approach would be to
  // clean up all of our buffers on error, but since the user must have elected
  // to turn on tracing, we assume that they would rather have a greater chance
  // of more information about what led up to the error rather than a greater
  // chance of avoiding a crash due to OOM.
  void handleError(JSContext* cx);

  void writeScriptUrl(ScriptSource* scriptSource);

  // Writes an atom into the outOfLineData_, associating it with the specified
  // id. In practice, `id` comes from an atom id inside a cache in the
  // JSContext which is incremented each time a new atom is registered and
  // cleared when tracing is done.
  bool writeAtom(JSContext* cx, JS::Handle<JSAtom*> atom, uint32_t id);
  bool writeFunctionFrame(JSContext* cx, AbstractFramePtr frame);

  // The below functions read data from the inlineData_ and outOfLineData_ ring
  // buffers into structs to be consumed by clients of the
  // JS_TracerSnapshotTrace API.
  bool readFunctionFrame(JS::ExecutionTrace::EventKind kind,
                         JS::ExecutionTrace::TracedEvent& event);
  bool readLabel(JS::ExecutionTrace::EventKind kind,
                 JS::ExecutionTrace::TracedEvent& event,
                 TracingScratchBuffer& scratchBuffer,
                 mozilla::Vector<char>& stringBuffer);
  bool readInlineEntry(mozilla::Vector<JS::ExecutionTrace::TracedEvent>& events,
                       TracingScratchBuffer& scratchBuffer,
                       mozilla::Vector<char>& stringBuffer);
  bool readOutOfLineEntry(
      mozilla::HashMap<uint32_t, size_t>& scriptUrls,
      mozilla::HashMap<uint32_t, size_t>& atoms,
      mozilla::Vector<JS::ExecutionTrace::ShapeSummary>& shapes,
      TracingScratchBuffer& scratchBuffer, mozilla::Vector<char>& stringBuffer);
  bool readInlineEntries(
      mozilla::Vector<JS::ExecutionTrace::TracedEvent>& events,
      TracingScratchBuffer& scratchBuffer, mozilla::Vector<char>& stringBuffer);
  bool readOutOfLineEntries(
      mozilla::HashMap<uint32_t, size_t>& scriptUrls,
      mozilla::HashMap<uint32_t, size_t>& atoms,
      mozilla::Vector<JS::ExecutionTrace::ShapeSummary>& shapes,
      TracingScratchBuffer& scratchBuffer, mozilla::Vector<char>& stringBuffer);

 public:
  ExecutionTracer() : bufferLock_(mutexid::ExecutionTracerInstanceLock) {}

  ~ExecutionTracer() {
    LockGuard<Mutex> guard(globalInstanceLock);

    globalInstances.eraseIfEqual(this);
  }

  mozilla::baseprofiler::BaseProfilerThreadId threadId() const {
    return threadId_;
  }

  bool init() {
    LockGuard<Mutex> guard(globalInstanceLock);
    LockGuard<Mutex> guard2(bufferLock_);

    threadId_ = mozilla::baseprofiler::profiler_current_thread_id();

    if (!inlineData_.init()) {
      return false;
    }
    if (!outOfLineData_.init()) {
      return false;
    }
    if (!valueData_.init()) {
      return false;
    }

    if (!globalInstances.append(this)) {
      return false;
    }

    valueSummaries_.init(&valueData_, &outOfLineData_);

    return true;
  }

  void onEnterFrame(JSContext* cx, AbstractFramePtr frame);
  void onLeaveFrame(JSContext* cx, AbstractFramePtr frame);

  template <typename CharType, JS::TracerStringEncoding Encoding>
  void onEnterLabel(const CharType* eventType);
  template <typename CharType, JS::TracerStringEncoding Encoding>
  void onLeaveLabel(const CharType* eventType);

  // Reads the execution trace from the underlying ring buffers and outputs it
  // into a native struct. For more information about this struct, see
  // js/public/Debug.h
  bool getNativeTrace(JS::ExecutionTrace::TracedJSContext& context,
                      TracingScratchBuffer& scratchBuffer,
                      mozilla::Vector<char>& stringBuffer);

  // Calls getNativeTrace for every JSContext in the process, populating the
  // provided ExecutionTrace with the result.
  static bool getNativeTraceForAllContexts(JS::ExecutionTrace& trace);
};

}  // namespace js

#endif /* debugger_ExecutionTracer_h */