TraceBuffer implementation with tests

runtime/vm/trace_buffer.h

Index: runtime/vm/trace_buffer.h
diff --git a/runtime/vm/trace_buffer.h b/runtime/vm/trace_buffer.h
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index 0000000000000000000000000000000000000000..f8b1c78de406e15451c8fb8cefbb36dcf68dd095
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+++ b/runtime/vm/trace_buffer.h
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+// Copyright (c) 2013, 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_TRACE_BUFFER_H_
+#define VM_TRACE_BUFFER_H_
+
+#include "platform/assert.h"
+#include "platform/globals.h"
+#include "vm/json_stream.h"
+
+namespace dart {
+
+class JSONStream;
+
+struct TraceBufferEntry {
+  int64_t micros;
+  char* message;
+  bool empty() const {
+    return message == NULL;
+  }
+};
+
+class TraceBuffer {
+ public:
+  static const intptr_t kDefaultCapacity = 1024;
+
+  explicit TraceBuffer(intptr_t capacity = kDefaultCapacity);
+  ~TraceBuffer();
+
+  void Clear();
+
+  // Internally message is copied.
+  void Trace(int64_t micros, const char* message);
+  // Internally message is copied.
+  void Trace(const char* message);
+  void TraceF(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
+
+  void PrintToJSONStream(JSONStream* stream) const;
+
+ private:
+  void Init();
+  void Cleanup();
+  void Fill(TraceBufferEntry* entry, int64_t micros, char* msg);
+  void AppendTrace(int64_t micros, char* message);
+
+  TraceBufferEntry* ring_;
+  const intptr_t ring_capacity_;
+  intptr_t ring_cursor_;
+
+  intptr_t RingIndex(intptr_t i) const {
+    return i % ring_capacity_;
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(TraceBuffer);
+};
+
+
+}  // namespace dart
+
+#endif  // VM_TRACE_BUFFER_H_