Initial GetSample implementation.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 73384946ba7d93594fd5c3d78753dfe01c2726f6..469dfdc477927bf415d73e4e0bc0b39b6a70bf81 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -1298,6 +1298,29 @@ class V8_EXPORT StackFrame {
 
 
 /**
+ * Isolate::Getsample collects the current JS execution state as a sample.
+ * A collected sample contains,
+ * - stack       : An array of addresses.
+ *                 One address per stack frame.
+ *                 The address is the instruction pointer,
+ *                 pointing to the instruction which led to the
+ *                 creation of the stack frame.
+ *                 (for example, a function call)
+ * - frames_count: Number of stack frames that were captured.
+ *                 That is, stack[frames_count+i] might contain meaningless
+ *                 addresses for any i >= 0.
+ */
+struct V8_EXPORT Sample {

[Benedikt Meurer, 2014/09/03 04:24:30]

I would really love to get rid of the public fields below, exposing the
internals is never a good idea, although I admit that it's unlikely that we will
ever change this. But how about this instead?

class V8_EXPORT Sample {
 public:
  enum { kMaxSize = 255u };

  Sample() : size_(0) {}
  template <class InputIterator> 
  Sample(InputIterator first, InputIterator last) : size_(0) {
    for (; first != last; ++first) data_[size_++] = *first;
  }

  typedef void const** const_iterator;
  const_iterator begin() const { return &data_[0]; }
  const_iterator end() const { return &data_[size_]; }
  size_t size() const { return size_; }

 private:
  void const* data_[kMaxSize];
  size_t size_;
};

Not super critical for the first version, but on the other hand this is public
API and we should not refactor it too often once landed, so maybe better have it
in from the beginning. WDYT?

[gholap, 2014/09/03 19:44:29]

Let us discuss this in person?

+  Sample()
+      : frames_count(0) {}
+  static const unsigned kMaxFramesCount = 255;

[Benedikt Meurer, 2014/09/03 04:24:30]

Should probably be

enum { kMaxFramesCount = 255u };

or otherwise requires a corresponding definition in an implementation file (we
had strange linker bugs with some compilers and code like this recently).

[gholap, 2014/09/03 19:44:29]

Done.

+
+  void* stack[kMaxFramesCount];  // Call stack.
+  unsigned frames_count;         // Number of captured frames.

[Benedikt Meurer, 2014/09/03 04:24:30]

I think this should be size_t instead of unsigned.

[gholap, 2014/09/03 19:44:29]

Done.

+};
+
+
+/**
  * A JSON Parser.
  */
 class V8_EXPORT JSON {
@@ -4217,6 +4240,11 @@ class V8_EXPORT Isolate {
   void GetHeapStatistics(HeapStatistics* heap_statistics);
 
   /**
+   * Get a sample from the isolate.
+   */
+  void GetSample(Sample* sample);
+
+  /**
    * Adjusts the amount of registered external memory. Used to give V8 an
    * indication of the amount of externally allocated memory that is kept alive
    * by JavaScript objects. V8 uses this to decide when to perform global