Add experimental support for tracing the state of the VM heap to a file

include/v8.h

Index: include/v8.h
===================================================================
--- include/v8.h	(revision 9457)
+++ include/v8.h	(working copy)
@@ -115,6 +115,7 @@
 class Heap;
 class HeapObject;
 class Isolate;
+class HeapVisualizerImplementation;
 }
 
 
@@ -682,6 +683,170 @@
 
 
 /**
+ * A heap visualization listener.
+ */
+// The linter thinks V8EXPORT is the class name.
+class V8EXPORT HeapVisualizer {  // NOLINT
+ public:
+  HeapVisualizer()
+      : next_(NULL),
+        pixel_size_log_2_(8),
+        buffer_fullness_(0),
+        secs_zero_(0) { }
+  virtual ~HeapVisualizer() { }
+  virtual void Write(const char* buf, int count) = 0;
+  virtual void Flush() {
+    Write(buffer_, buffer_fullness_);
+    buffer_fullness_ = 0;
+  }
+
+  static const int kHeapOverheadPseudoSpaceIdentity = 10;
+  static const int kSurvivingNewSpacePseudoSpaceIdentity = 11;
+
+  typedef enum {
+    kAllocated,  // start_w len_w transparency-byte transparency-byte ...
+    kConstantAllocation,  // start_w len_w transparency-byte
+    kChangeAllocation,  // start_w, change-byte
+    kNameArea,   // space-code-byte start_w len_w
+    kFreeArea,   // start_w len_w
+    kWritten,    //    "      "
+    kRead,       //    "      "
+    kSwept,      //    "      "
+    kMarked,     //    "      "
+    kTimeStamp   // s_w us_w
+  } MessageId;
+
+  typedef enum {
+    kRunning,
+    kCrankshafting,
+    kScavenging,
+    kMarking,
+    kCompacting,
+    kSweeping
+  } ProfileState;
+
+  intptr_t pixel_size_log_2() { return pixel_size_log_2_; }
+  virtual void set_pixel_size_log_2(uintptr_t pixel_size_log_2) {
+    pixel_size_log_2_ = pixel_size_log_2;
+  }
+
+  uint32_t secs_zero() { return secs_zero_; }
+  uint32_t usecs_zero() { return usecs_zero_; }
+  void set_time_zero(uint32_t secs, uint32_t usecs) {
+    secs_zero_ = secs;
+    usecs_zero_ = usecs;
+  }
+
+  // These methods don't necessarily have to be here, but they server
+  // as a sort of documentation of the protocol.
+
+  // The protocol describes the state of the heap at a (currently implicit)
+  // granularity of 'pixels'.  A pixel is some power-of-2 number of bytes.
+
+  // A graymap that indicates how full a set of |size| consecutive pixels of
+  // memory are.  0 indicates that all bytes in a pixel are allocated.  255
+  // indicates that all bytes in a pixel are free.
+  void Allocate(uintptr_t address, uintptr_t size, unsigned char* freeness) {
+    Write8(kAllocated);
+    Write32(address >> pixel_size_log_2_);
+    Write32(size);
+    WriteX(freeness, size);
+  }
+
+  // A way to quickly set the allocatedness of a set of pixels to the same
+  // value.  Normally the freeness will be 0 (all bytes allocated) or 255 (all
+  // bytes free).
+  void ConstantAllocation(
+      uintptr_t address, uintptr_t size, unsigned char freeness) {
+    Write8(kConstantAllocation);
+    Write32(address >> pixel_size_log_2_);
+    Write32(size >> pixel_size_log_2_);
+    Write8(freeness);
+  }
+
+  // A way to indicate that a number of bytes have been allocated within a
+  // pixel.  The resolution is limited unless a pixel is smaller than 256
+  // bytes, since there are only 8 bits of precision in the final byte which
+  // indicates how many bytes have been allocated from 0 to 255 (representing
+  // all the bytes in the pixel).
+  void ChangeAllocation(uintptr_t address, uintptr_t change) {
+    Write8(kChangeAllocation);
+    Write32(address >> pixel_size_log_2_);
+    uintptr_t change_byte = change >> pixel_size_log_2_;
+    Write8(change_byte == 256 ? 255 : change_byte);
+  }
+
+  // Indicates for a range of memory that it has been allocated from the OS and
+  // dedicated to a particular use in the heap.  The |space| argument is a
+  // space id from spaces.h or one of the pseudo-space-identities defined in
+  // this class.
+  void Name(int space, uintptr_t address, uintptr_t size) {
+    Write8(kNameArea);
+    Write8(space);
+    Write32(address >> pixel_size_log_2_);
+    Write32(size >> pixel_size_log_2_);
+  }
+
+  // Currently unused way of indicating that something has happened in a region
+  // of memory.
+  void Event(MessageId id, uintptr_t address, uintptr_t size) {
+    Write8(id);
+    Write32(address >> pixel_size_log_2_);
+    Write32(size >> pixel_size_log_2_);
+  }
+
+  // Transmit the time since the VM started in seconds and microseconds.  Also
+  // transmits a VM state.  The VM is assumed to transition into the given
+  // state at the time indicated, so the time up to the indicated time is
+  // assumed to have been spent in the previous state.
+  void TimeStamp(int state, uintptr_t s, uintptr_t us) {
+    Write8(kTimeStamp);
+    Write8(state);
+    Write32(s);
+    Write32(us);
+  }
+
+  HeapVisualizer* next() { return next_; }
+
+ private:
+  static const int kBufferSize = 4096;
+
+  HeapVisualizer* next_;
+  uintptr_t pixel_size_log_2_;
+  int buffer_fullness_;
+  uint32_t secs_zero_;
+  uint32_t usecs_zero_;
+  char buffer_[kBufferSize];
+
+  void set_next(HeapVisualizer* next) { next_ = next; }
+
+  // Little endian 32 bit value.
+  inline void Write32(intptr_t x) {
+    if (kBufferSize - buffer_fullness_ < 4) {
+      Flush();
+    }
+    buffer_[buffer_fullness_] = x >> 24;
+    buffer_[buffer_fullness_ + 1] = x >> 16;
+    buffer_[buffer_fullness_ + 2] = x >> 8;
+    buffer_[buffer_fullness_ + 3] = x;
+    buffer_fullness_ += 4;
+  }
+
+  inline void Write8(int x) {
+    if (kBufferSize == buffer_fullness_) Flush();
+    buffer_[buffer_fullness_++] = x;
+  }
+
+  void WriteX(unsigned char* bytes, int len);
+
+  friend class v8::internal::HeapVisualizerImplementation;
+};
+
+
+void V8EXPORT RegisterHeapVisualizer(HeapVisualizer* visualizer);
+
+
+/**
  * An error message.
  */
 class V8EXPORT Message {