Implement a heap profiler for the Dart managed heap.

runtime/vm/heap_profiler.cc

Index: runtime/vm/heap_profiler.cc
diff --git a/runtime/vm/heap_profiler.cc b/runtime/vm/heap_profiler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e4d2c6cae91000f03a967473b1fa7615c7729e0d
--- /dev/null
+++ b/runtime/vm/heap_profiler.cc
@@ -0,0 +1,715 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/heap_profiler.h"
+
+#include <stdio.h>
+#include <arpa/inet.h>
+#include <sys/time.h>
+
+#include "vm/dart_api_state.h"
+#include "vm/object.h"
+#include "vm/raw_object.h"
+#include "vm/stack_frame.h"
+#include "vm/unicode.h"
+
+namespace dart {
+
+HeapProfiler::Buffer::~Buffer() {
+  delete[] data_;
+}
+
+
+void HeapProfiler::Buffer::Write(const uint8_t* data, intptr_t size) {
+  EnsureCapacity(size);
+  memmove(&data_[size_], data, size);
+  size_ += size;

[turnidge, 2012/06/12 17:02:19]

It's a bit confusing to me to have both "name_" and "name" in play at the same
time in a non-trivial way.  If you can think of a convenient rename for the
member or the parameter, that would help folks like me.  Your call.

[cshapiro, 2012/06/14 00:08:36]

I see where you are coming from.  I would like this to be as readable as
possible.  Can you suggest new names for data and size?

+}
+
+
+void HeapProfiler::Buffer::EnsureCapacity(intptr_t size) {
+  if ((size + size_) > capacity_) {
+    intptr_t new_capacity = Utils::RoundUpToPowerOfTwo(capacity_ + size);
+    uint8_t* new_data = new uint8_t[new_capacity];
+    memmove(new_data, data_, size_);
+    capacity_ = new_capacity;
+    data_ = new_data;
+  }
+}
+
+
+void HeapProfiler::Record::Write(const uint8_t* value, intptr_t size) {
+  body_.Write(value, size);
+}
+
+
+void HeapProfiler::Record::Write8(uint8_t value) {
+  body_.Write(&value, sizeof(value));
+}
+
+
+void HeapProfiler::Record::Write16(uint16_t value) {
+  value = htons(value);
+  body_.Write(reinterpret_cast<uint8_t*>(&value), sizeof(value));
+}
+
+
+void HeapProfiler::Record::Write32(uint32_t value) {
+  value = htonl(value);
+  body_.Write(reinterpret_cast<uint8_t*>(&value), sizeof(value));
+}
+
+
+void HeapProfiler::Record::Write64(uint64_t value) {
+  uint16_t x = 0xFF;
+  if (*reinterpret_cast<uint8_t*>(&x) == 0xFF) {
+    uint64_t hi = static_cast<uint64_t>(htonl(value & 0xFFFFFFFF)) << 32;
+    uint64_t lo = htonl(value >> 32);
+    value = hi | lo;
+  }
+  body_.Write(reinterpret_cast<uint8_t*>(&value), sizeof(value));
+}
+
+
+void HeapProfiler::Record::WritePointer(const void* value) {
+  if (sizeof(value) == 4) {
+    Write32(reinterpret_cast<uint32_t>(value));
+  } else {
+    ASSERT(sizeof(value) == 8);
+    Write64(reinterpret_cast<uint64_t>(value));
+  }
+}
+
+
+HeapProfiler::SubRecord::SubRecord(uint8_t sub_tag, HeapProfiler* profiler)
+    : record_(profiler->heap_dump_record_) {
+  record_->Write8(sub_tag);
+}
+
+
+HeapProfiler::SubRecord::~SubRecord() {
+}
+
+
+void HeapProfiler::SubRecord::Write(const uint8_t* value, intptr_t size) {
+  record_->Write(value, size);
+}
+
+
+void HeapProfiler::SubRecord::Write8(uint8_t value) {
+  record_->Write8(value);
+}
+
+
+void HeapProfiler::SubRecord::Write16(uint16_t value) {
+  record_->Write16(value);
+}
+
+
+void HeapProfiler::SubRecord::Write32(uint32_t value) {
+  record_->Write32(value);
+}
+
+
+void HeapProfiler::SubRecord::Write64(uint64_t value) {
+  record_->Write64(value);
+}
+
+
+void HeapProfiler::SubRecord::WritePointer(const void* value) {
+  record_->WritePointer(value);
+}
+
+
+HeapProfiler::HeapProfiler(Dart_HeapProfileWriteCallback callback, void* stream)
+    : write_callback_(callback),
+      output_stream_(stream),
+      heap_dump_record_(NULL) {
+  WriteHeader();
+  WriteStackTrace();
+  heap_dump_record_ = new Record(kHeapDump, this);
+}
+
+
+HeapProfiler::~HeapProfiler() {
+  delete heap_dump_record_;
+}
+
+
+const RawObject* HeapProfiler::ObjectId(const RawObject* raw_obj) {
+  if (!raw_obj->IsHeapObject()) {
+    // To describe an immediate object in HPROF we record its value
+    // and write fake INSTANCE_DUMP subrecord in the HEAP_DUMP record.
+    const RawSmi* raw_smi = reinterpret_cast<const RawSmi*>(raw_obj);
+    if (smi_table_.find(raw_smi) == smi_table_.end()) {
+      smi_table_.insert(raw_smi);
+    }
+  } else if (raw_obj->GetClassId() == kNullClassId) {
+    // Instances of the Null type are translated to NULL so they can
+    // be printed as "null" in HAT.
+    return NULL;
+  }
+  return raw_obj;
+}
+
+
+const RawClass* HeapProfiler::ClassId(const RawClass* raw_class) {
+  // A unique LOAD_CLASS record must be written for each class object.
+  if (class_table_.find(raw_class) == class_table_.end()) {
+    class_table_.insert(raw_class);
+    WriteLoadClass(raw_class);
+  }
+  return raw_class;
+}
+
+
+// A built-in class may have its name encoded in a C-string.  These
+// strings should only be found in class objects.  We emit a unique
+// STRING_IN_UTF8 so HAT will properly display the class name.
+const char* HeapProfiler::StringId(const char* c_string) {
+  const RawString* ptr = reinterpret_cast<const RawString*>(c_string);
+  if (string_table_.find(ptr) == string_table_.end()) {
+    string_table_.insert(ptr);
+    WriteStringInUtf8(c_string);
+  }
+  return c_string;
+}
+
+
+const RawString* HeapProfiler::StringId(const RawString* raw_string) {
+  // A unique STRING_IN_UTF8 record must be written for each string
+  // object.
+  if (string_table_.find(raw_string) == string_table_.end()) {
+    string_table_.insert(raw_string);
+    WriteStringInUtf8(raw_string);
+  }
+  return raw_string;
+}
+
+
+void HeapProfiler::WriteRoot(const RawObject* raw_obj) {
+  SubRecord sub(kRootUnknown, this);
+  sub.WritePointer(ObjectId(raw_obj));
+}
+
+
+void HeapProfiler::WriteObject(const RawObject* raw_obj) {
+  ASSERT(raw_obj->IsHeapObject());
+  if (FreeListElement::IsSpecialClass(raw_obj)) {
+    // Free space has an object-like encoding.  Heap profiles only
+    // care about live objects so we skip over these records.
+    return;
+  }
+  ObjectKind kind = raw_obj->ptr()->class_->ptr()->instance_kind_;
+  switch (kind) {
+    case Class::kInstanceKind: {
+      WriteClassDump(reinterpret_cast<const RawClass*>(raw_obj));
+      break;
+    }
+    case Array::kInstanceKind:
+    case ImmutableArray::kInstanceKind: {
+      WriteObjectArrayDump(reinterpret_cast<const RawArray*>(raw_obj));
+      break;
+    }
+    case Int8Array::kInstanceKind:
+    case Uint8Array::kInstanceKind: {
+      const RawInt8Array* raw_int8_array =
+          reinterpret_cast<const RawInt8Array*>(raw_obj);
+      WritePrimitiveArrayDump(raw_int8_array,
+                              kByte,
+                              &raw_int8_array->data_[0]);
+      break;
+    }
+    case Int16Array::kInstanceKind:
+    case Uint16Array::kInstanceKind: {
+      const RawInt16Array* raw_int16_array =
+          reinterpret_cast<const RawInt16Array*>(raw_obj);
+      WritePrimitiveArrayDump(raw_int16_array,
+                              kShort,
+                              &raw_int16_array->data_[0]);
+      break;
+    }
+    case Int32Array::kInstanceKind:
+    case Uint32Array::kInstanceKind: {
+      const RawInt32Array* raw_int32_array =
+          reinterpret_cast<const RawInt32Array*>(raw_obj);
+      WritePrimitiveArrayDump(raw_int32_array,
+                              kInt,
+                              &raw_int32_array->data_[0]);
+      break;
+    }
+    case Int64Array::kInstanceKind:
+    case Uint64Array::kInstanceKind: {
+      const RawInt64Array* raw_int64_array =
+          reinterpret_cast<const RawInt64Array*>(raw_obj);
+      WritePrimitiveArrayDump(raw_int64_array,
+                              kLong,
+                              &raw_int64_array->data_[0]);
+      break;
+    }
+    case Float32Array::kInstanceKind: {
+      const RawFloat32Array* raw_float32_array =
+          reinterpret_cast<const RawFloat32Array*>(raw_obj);
+      WritePrimitiveArrayDump(raw_float32_array,
+                              kFloat,
+                              &raw_float32_array->data_[0]);
+      break;
+    }
+    case Float64Array::kInstanceKind: {
+      const RawFloat64Array* raw_float64_array =
+          reinterpret_cast<const RawFloat64Array*>(raw_obj);
+      WritePrimitiveArrayDump(raw_float64_array,
+                              kDouble,
+                              &raw_float64_array->data_[0]);
+      break;
+    }
+    case OneByteString::kInstanceKind:
+    case TwoByteString::kInstanceKind:
+    case FourByteString::kInstanceKind:
+    case ExternalOneByteString::kInstanceKind:
+    case ExternalTwoByteString::kInstanceKind:
+    case ExternalFourByteString::kInstanceKind: {
+      WriteInstanceDump(StringId(reinterpret_cast<const RawString*>(raw_obj)));
+      break;
+    }
+    default:
+      WriteInstanceDump(raw_obj);
+  }
+}
+
+
+void HeapProfiler::Write(const void* data, intptr_t size) {
+  (*write_callback_)(data, size, output_stream_);
+}
+
+
+// Header
+//
+// Format:
+//   [u1]* - format name
+//   u4 - size of identifiers
+//   u4 - high word of number of milliseconds since 0:00 GMT, 1/1/70
+//   u4 - low word of number of milliseconds since 0:00 GMT, 1/1/70
+void HeapProfiler::WriteHeader() {
+  const char magic[] = "JAVA PROFILE 1.0.1";
+  Write(magic, sizeof(magic));
+  uint32_t size = htonl(kWordSize);
+  Write(&size, sizeof(size));
+  uint64_t milliseconds = OS::GetCurrentTimeMillis();
+  uint32_t hi = htonl((uint32_t)((milliseconds >> 32) & 0x00000000FFFFFFFF));
+  Write(&hi, sizeof(hi));
+  uint32_t lo = htonl((uint32_t)(milliseconds & 0x00000000FFFFFFFF));
+  Write(&lo, sizeof(lo));
+}
+
+
+// Record
+//
+// Format:
+//   u1 - TAG: denoting the type of the record
+//   u4 - TIME: number of microseconds since the time stamp in the header
+//   u4 - LENGTH: number of bytes that follow this u4 field and belong
+//        to this record
+//   [u1]* - BODY: as many bytes as specified in the above u4 field
+void HeapProfiler::WriteRecord(const Record& record) {
+  uint8_t tag = record.Tag();
+  Write(&tag, sizeof(tag));
+  uint32_t time = htonl(record.Time());
+  Write(&time, sizeof(time));
+  uint32_t length = htonl(record.Length());
+  Write(&length, sizeof(length));
+  Write(record.Body(), record.Length());
+}
+
+
+// STRING IN UTF8 - 0x01
+//
+// Format:
+//   ID - ID for this string
+//   [u1]* - UTF8 characters for string (NOT NULL terminated)
+void HeapProfiler::WriteStringInUtf8(const RawString* raw_string) {
+  intptr_t length = 0;
+  char* characters = NULL;
+  ObjectKind kind = raw_string->ptr()->class_->ptr()->instance_kind_;
+  if (kind == OneByteString::kInstanceKind) {
+    const RawOneByteString* onestr =
+        reinterpret_cast<const RawOneByteString*>(raw_string);
+    for (intptr_t i = 0; i < Smi::Value(onestr->ptr()->length_); ++i) {
+      length += Utf8::Length(onestr->ptr()->data_[i]);
+    }
+    characters = new char[length];
+    for (intptr_t i = 0, j = 0; i < Smi::Value(onestr->ptr()->length_); ++i) {
+      int32_t ch = onestr->ptr()->data_[i];
+      j += Utf8::Encode(ch, &characters[j]);
+    }
+  } else if (kind == TwoByteString::kInstanceKind) {
+    const RawTwoByteString* twostr =
+        reinterpret_cast<const RawTwoByteString*>(raw_string);
+    for (intptr_t i = 0; i < Smi::Value(twostr->ptr()->length_); ++i) {
+      length += Utf8::Length(twostr->ptr()->data_[i]);
+    }
+    characters = new char[length];
+    for (intptr_t i = 0, j = 0; i < Smi::Value(twostr->ptr()->length_); ++i) {
+      int32_t ch = twostr->ptr()->data_[i];
+      j += Utf8::Encode(ch, &characters[j]);
+    }
+  } else {
+    ASSERT(kind == FourByteString::kInstanceKind);
+    const RawFourByteString* fourstr =
+        reinterpret_cast<const RawFourByteString*>(raw_string);
+    for (intptr_t i = 0; i < Smi::Value(fourstr->ptr()->length_); ++i) {
+      length += Utf8::Length(fourstr->ptr()->data_[i]);
+    }
+    characters = new char[length];
+    for (intptr_t i = 0, j = 0; i < Smi::Value(fourstr->ptr()->length_); ++i) {
+      int32_t ch = fourstr->ptr()->data_[i];
+      j += Utf8::Encode(ch, &characters[j]);
+    }
+  }
+  Record record(kStringInUtf8, this);
+  record.WritePointer(ObjectId(raw_string));
+  for (intptr_t i = 0; i < length; ++i) {
+    record.Write8(characters[i]);
+  }
+  delete[] characters;
+}
+
+
+void HeapProfiler::WriteStringInUtf8(const char* c_string) {
+  Record record(kStringInUtf8, this);
+  record.WritePointer(c_string);
+  for (; *c_string != '\0'; ++c_string) {
+    record.Write8(*c_string);
+  }
+}
+
+
+// LOAD CLASS - 0x02
+//
+// Format:
+//   u4 - class serial number (always > 0)
+//   ID - class object ID
+//   u4 - stack trace serial number
+//   ID - class name string ID
+void HeapProfiler::WriteLoadClass(const RawClass* raw_class) {
+  Record record(kLoadClass, this);
+  // class serial number (always > 0)
+  record.Write32(1);
+  // class object ID
+  record.WritePointer(raw_class);
+  // stack trace serial number
+  record.Write32(0);
+  if (raw_class->ptr()->name_ == String::null()) {
+    intptr_t class_index = Object::GetSingletonClassIndex(raw_class);
+    const char* name = Object::GetSingletonClassName(class_index);
+    record.WritePointer(StringId(name));
+  } else {
+    record.WritePointer(StringId(raw_class->ptr()->name_));
+  }
+}
+
+
+// STACK TRACE - 0x05
+//
+//  u4 - stack trace serial number
+//  u4 - thread serial number
+//  u4 - number of frames
+//  [ID]* - series of stack frame ID's
+void HeapProfiler::WriteStackTrace() {
+  Record record(kStackTrace, this);
+  // stack trace serial number
+  record.Write32(0);
+  // thread serial number
+  record.Write32(0);
+  // number of frames
+  record.Write32(0);
+}
+
+
+// HEAP SUMMARY - 0x07
+//
+// Format:
+//   u4 - total live bytes
+//   u4 - total live instances
+//   u8 - total bytes allocated
+//   u8 - total instances allocated
+void HeapProfiler::WriteHeapSummary(uint32_t total_live_bytes,
+                                   uint32_t total_live_instances,
+                                   uint64_t total_bytes_allocated,
+                                   uint64_t total_instances_allocated) {
+  Record record(kHeapSummary, this);
+  record.Write32(total_live_bytes);
+  record.Write32(total_live_instances);
+  record.Write32(total_bytes_allocated);
+  record.Write32(total_instances_allocated);
+}
+
+
+// HEAP DUMP - 0x0C
+//
+// Format:
+//  []*
+void HeapProfiler::WriteHeapDump() {
+  Record record(kHeapDump, this);
+}
+
+
+// CLASS DUMP - 0x20
+//
+// Format:
+//  ID - class object ID
+//  u4 - stack trace serial number
+//  ID - super class object ID
+//  ID - class loader object ID
+//  ID - signers object ID
+//  ID - protection domain object ID
+//  ID - reserved
+//  ID - reserved
+//  u4 - instance size (in bytes)
+//  u2 - size of constant pool and number of records that follow:
+//  u2 - constant pool index
+//  u1 - type of entry: (See Basic Type)
+//  value - value of entry (u1, u2, u4, or u8 based on type of entry)
+//  u2 - Number of static fields:
+//  ID - static field name string ID
+//  u1 - type of field: (See Basic Type)
+//  value - value of entry (u1, u2, u4, or u8 based on type of field)
+//  u2 - Number of instance fields (not including super class's)
+//  ID - field name string ID
+//  u1 - type of field: (See Basic Type)
+void HeapProfiler::WriteClassDump(const RawClass* raw_class) {
+  SubRecord sub(kClassDump, this);
+  // class object ID
+  sub.WritePointer(ClassId(raw_class));
+  // stack trace serial number
+  sub.Write32(0);
+  // super class object ID
+  if (raw_class == raw_class->ptr()->class_) {
+    sub.WritePointer(NULL);
+  } else {
+    sub.WritePointer(ClassId(raw_class->ptr()->class_));
+  }
+  // class loader object ID
+  sub.WritePointer(NULL);
+  // signers object ID
+  sub.WritePointer(NULL);
+  // protection domain object ID
+  sub.WritePointer(NULL);
+  // reserved
+  sub.WritePointer(NULL);
+  // reserved
+  sub.WritePointer(NULL);
+
+  intptr_t num_static_fields = 0;
+  intptr_t num_instance_fields = 0;
+
+  RawArray* raw_array = raw_class->ptr()->fields_;
+  if (raw_array != Array::null()) {
+    for (intptr_t i = 0; i < Smi::Value(raw_array->ptr()->length_); ++i) {
+      RawField* raw_field =
+          reinterpret_cast<RawField*>(raw_array->ptr()->data()[i]);
+      if (raw_field->ptr()->is_static_) {
+        ++num_static_fields;
+      } else {
+        ++num_instance_fields;
+      }
+    }
+  }
+  // instance size (in bytes)
+  sub.Write32(sizeof(RawClass));

[turnidge, 2012/06/12 17:02:19]

What is the instance size supposed to mean for a class?

[cshapiro, 2012/06/14 00:08:36]

It is the size of instances, not the size of the class object we are dumping.  I
have adjusted the code and added a comment about this.  At present, we do not
handle variable sized objects well and many internal classes have an
indeterminate length.

+  // size of constant pool and number of records that follow:
+  sub.Write16(0);
+  // Number of static fields
+  sub.Write16(num_static_fields);
+  // Static fields:
+  if (raw_array != Array::null()) {
+    for (intptr_t i = 0; i < Smi::Value(raw_array->ptr()->length_); ++i) {
+      RawField* raw_field =
+          reinterpret_cast<RawField*>(raw_array->ptr()->data()[i]);
+      if (raw_field->ptr()->is_static_) {
+        ASSERT(raw_field->ptr()->name_ != String::null());
+        // static field name string ID
+        sub.WritePointer(StringId(raw_field->ptr()->name_));
+        // type of static field
+        sub.Write8(kObject);
+        // value of entry
+        sub.WritePointer(ObjectId(raw_field->ptr()->value_));
+      }
+    }
+  }
+  // Number of instance fields (not include super class's)
+  sub.Write16(num_instance_fields);
+  // Instance fields:
+  if (raw_array != Array::null()) {
+    for (intptr_t i = 0; i < Smi::Value(raw_array->ptr()->length_); ++i) {
+      RawField* raw_field =
+          reinterpret_cast<RawField*>(raw_array->ptr()->data()[i]);
+      if (!raw_field->ptr()->is_static_) {
+        ASSERT(raw_field->ptr()->name_ != String::null());
+        // field name string ID
+        sub.WritePointer(StringId(raw_field->ptr()->name_));
+        // type of field
+        sub.Write8(kObject);
+      }
+    }
+  }
+}
+
+
+// INSTANCE DUMP - 0x21
+//
+// Format:
+//  ID - object ID
+//  u4 - stack trace serial number
+//  ID - class object ID
+//  u4 - number of bytes that follow
+//  [value]* - instance field values (this class, followed by super class, etc)
+void HeapProfiler::WriteInstanceDump(const RawObject* raw_obj) {
+  SubRecord sub(kInstanceDump, this);
+  // object ID
+  sub.WritePointer(raw_obj);
+  // stack trace serial number
+  sub.Write32(0);
+  // class object ID
+  sub.WritePointer(ClassId(raw_obj->ptr()->class_));
+  // number of bytes that follow
+  intptr_t num_instance_fields = 0;
+  for (RawClass* cls = raw_obj->ptr()->class_;
+       cls != cls->ptr()->class_;
+       cls = cls->ptr()->class_) {
+    RawArray* raw_array = cls->ptr()->fields_;
+    if (raw_array != Array::null()) {
+      intptr_t length = Smi::Value(raw_array->ptr()->length_);
+      for (intptr_t i = 0; i < length; ++i) {
+        RawField* raw_field =
+            reinterpret_cast<RawField*>(raw_array->ptr()->data()[i]);
+        if (!raw_field->ptr()->is_static_) {
+          ++num_instance_fields;
+        }
+      }
+    }
+  }
+  sub.Write32(num_instance_fields * kWordSize);
+  // instance field values (this class, followed by super class, etc)
+  for (RawClass* cls = raw_obj->ptr()->class_;
+       cls != cls->ptr()->class_;
+       cls = cls->ptr()->class_) {
+    RawArray* raw_array = cls->ptr()->fields_;
+    if (raw_array != Array::null()) {
+      intptr_t length = Smi::Value(raw_array->ptr()->length_);
+      uint8_t* base = reinterpret_cast<uint8_t*>(raw_obj->ptr());
+      for (intptr_t i = 0; i < length; ++i) {
+        RawField* raw_field =
+            reinterpret_cast<RawField*>(raw_array->ptr()->data()[i]);
+        if (!raw_field->ptr()->is_static_) {
+          intptr_t offset =
+              Smi::Value(reinterpret_cast<RawSmi*>(raw_field->ptr()->value_));
+          RawObject* ptr = *reinterpret_cast<RawObject**>(base + offset);
+          sub.WritePointer(ObjectId(ptr));
+        }
+      }
+    }
+  }
+}
+
+
+// OBJECT ARRAY DUMP - 0x22
+//
+// Format:
+//  ID - array object ID
+//  u4 - stack trace serial number
+//  u4 - number of elements
+//  ID - array class object ID
+//  [ID]* - elements
+void HeapProfiler::WriteObjectArrayDump(const RawArray* raw_array) {
+  SubRecord sub(kObjectArrayDump, this);
+  // array object ID
+  sub.WritePointer(raw_array);
+  // stack trace serial number
+  sub.Write32(0);
+  // number of elements
+  intptr_t length = Smi::Value(raw_array->ptr()->length_);
+  sub.Write32(length);
+  // array class object ID
+  sub.WritePointer(NULL);
+  // elements
+  for (intptr_t i = 0; i < length; ++i) {
+    sub.WritePointer(ObjectId(raw_array->ptr()->data()[i]));
+  }
+}
+
+
+// PRIMITIVE ARRAY DUMP - 0x23
+//
+// Format:
+//  ID - array object ID
+//  u4 - stack trace serial number
+//  u4 - number of elements
+//  u1 - element type
+//  [u1]* - elements
+void HeapProfiler::WritePrimitiveArrayDump(const RawByteArray* raw_byte_array,
+                                           uint8_t tag,
+                                           const void* data) {
+  SubRecord sub(kPrimitiveArrayDump, this);
+  // array object ID
+  sub.WritePointer(raw_byte_array);
+  // stack trace serial number
+  sub.Write32(0);
+  // number of elements
+  intptr_t length = Smi::Value(raw_byte_array->ptr()->length_);
+  sub.Write32(length);
+  // element type
+  sub.Write8(tag);
+  // elements (packed)
+  for (intptr_t i = 0; i < length; ++i) {
+    if (tag == kByte) {
+      sub.Write8(reinterpret_cast<const int8_t*>(data)[i]);
+    } else if (tag == kShort) {
+      sub.Write16(reinterpret_cast<const int16_t*>(data)[i]);
+      break;
+    } else if (tag == kInt || tag == kFloat) {
+      sub.Write32(reinterpret_cast<const int32_t*>(data)[i]);
+    } else {
+      ASSERT(tag == kLong || tag == kDouble);
+      sub.Write64(reinterpret_cast<const int64_t*>(data)[i]);
+    }
+  }
+}
+
+
+void HeapProfilerRootVisitor::VisitPointers(RawObject** first,
+                                           RawObject** last) {
+  for (RawObject** current = first; current <= last; current++) {
+    RawObject* raw_obj = *current;
+    if (raw_obj->IsHeapObject()) {
+      // Skip visits of FreeListElements.
+      if (FreeListElement::IsSpecialClass(raw_obj)) {
+        // Only the class of the free list element should ever be visited.
+        ASSERT(first == last);
+        return;
+      }
+      uword obj_addr = RawObject::ToAddr(raw_obj);
+      if (!Isolate::Current()->heap()->Contains(obj_addr) &&
+          !Dart::vm_isolate()->heap()->Contains(obj_addr)) {
+        FATAL1("Invalid object pointer encountered 0x%lx\n", obj_addr);
+      }
+    }
+    profiler_->WriteRoot(raw_obj);
+  }
+}
+
+
+void HeapProfilerWeakRootVisitor::VisitHandle(uword addr) {
+  FinalizablePersistentHandle* handle =
+      reinterpret_cast<FinalizablePersistentHandle*>(addr);
+  RawObject* raw_obj = handle->raw();
+  visitor_->VisitPointer(&raw_obj);
+}
+
+
+void HeapProfilerObjectVisitor::VisitObject(RawObject* raw_obj) {
+  profiler_->WriteObject(raw_obj);
+}
+
+}  // namespace dart