Light-weight stats counters for experiments.

runtime/vm/counters.h

Index: runtime/vm/counters.h
===================================================================
--- runtime/vm/counters.h	(revision 0)
+++ runtime/vm/counters.h	(revision 0)
@@ -0,0 +1,51 @@
+// Copyright (c) 2014, 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.
+
+#ifndef VM_COUNTERS_H_
+#define VM_COUNTERS_H_
+
+#include "platform/assert.h"
+
+namespace dart {
+
+struct Counter {
+  Counter() : name(NULL), value(0) {}
+  const char* name;
+  int64_t value;
+};
+
+
+// Light-weight stats counters for temporary experiments/debugging.
+// A single statement is enough to add a counter:
+//   ...
+//   Isolate::Current()->counters()->Increment("allocated", size_in_bytes);
+//   ...
+class Counters {
+ public:
+  Counters() : collision_(false) {}
+
+  // Adds 'delta' to the named counter. 'name' must be a literal string.
+  void Increment(const char* name, int64_t delta) {
+    Counter& counter =
+      counters_[reinterpret_cast<uword>(name) & (kSize - 1)];
+    if (counter.name != name && counter.name != NULL) {
+      collision_ = true;
+    }
+    counter.name = name;
+    counter.value += delta;
+  }
+
+  // Prints all counters to stderr.
+  ~Counters();
+
+ private:
+  enum { kSize = 1024 };
+  COMPILE_ASSERT((0 == (kSize & (kSize - 1))));  // kSize is a power of 2.
+  Counter counters_[kSize];
+  bool collision_;
+};
+
+}  // namespace dart
+
+#endif  // VM_COUNTERS_H_