Chrome tracing for system-wide performance stats.

base/debug/trace_event_system_stats_monitor.h

Index: base/debug/trace_event_system_stats_monitor.h
diff --git a/base/debug/trace_event_system_stats_monitor.h b/base/debug/trace_event_system_stats_monitor.h
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@@ -0,0 +1,77 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_DEBUG_TRACE_EVENT_SYSTEM_STATS_MONITOR_H_
+#define BASE_DEBUG_TRACE_EVENT_SYSTEM_STATS_MONITOR_H_
+
+#include "base/base_export.h"
+#include "base/debug/trace_event_impl.h"
+#include "base/gtest_prod_util.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/process/process_metrics.h"
+#include "base/timer/timer.h"
+
+namespace base {
+
+class MessageLoopProxy;
+
+namespace debug {
+
+// Watches for chrome://tracing to be enabled or disabled. When tracing is
+// enabled, also enables system events profiling. This class is the preferred
+// way to turn system tracing on and off.
+class BASE_EXPORT TraceEventSystemStatsMonitor
+    : public TraceLog::EnabledStateObserver {
+ public:
+  // Length of time interval between stat profiles.
+  static const int kSystemStatsMonitorIntervalSeconds = 2;

[nduca, 2013/09/07 07:19:20]

I'd suggest making this unit in milliseconds, e.g. 2000, and use
TimeTicks::FromMilliseconds in the other. That way if we ever want to turn it
up, we can turn it up faster than 1s intervals. :)

[jwmak, 2013/09/08 09:26:05]

Done.

+
+  // |message_loop_proxy| must be a proxy to the primary thread for the client
+  // process, e.g. the UI thread in a browser.
+  explicit TraceEventSystemStatsMonitor(
+      scoped_refptr<MessageLoopProxy> message_loop_proxy);
+
+  virtual ~TraceEventSystemStatsMonitor();
+
+  // base::debug::TraceLog::EnabledStateChangedObserver overrides:
+  virtual void OnTraceLogEnabled() OVERRIDE;
+  virtual void OnTraceLogDisabled() OVERRIDE;
+
+  // Starts system profiling.
+  void StartProfiling();

[nduca, 2013/09/07 07:19:20]

this doesn't have to be public --- start/stop and dump can all be private.

I'dkill the comments. we generally only add comments when they add value. its
sort of like defining a word using itself, ya know?

[jwmak, 2013/09/08 09:26:05]

Done.

+
+  // Retrieves system profiling.
+  void DumpSystemStats();
+
+  // Ends system profiling.
+  void StopProfiling();
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(TraceSystemStatsMonitorTest,
+                           TraceEventSystemStatsMonitor);
+
+  bool IsTimerRunningForTest() const;
+
+  // Ensures the observer starts and stops tracing on the primary thread.
+  scoped_refptr<MessageLoopProxy> message_loop_proxy_;
+
+  // Timer to schedule system profile dumps.
+  RepeatingTimer<TraceEventSystemStatsMonitor> dump_timer_;
+
+  WeakPtrFactory<TraceEventSystemStatsMonitor> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(TraceEventSystemStatsMonitor);
+};
+
+// Converts system memory profiling stats in |input| to
+// trace event compatible JSON and appends to |output|. Visible for testing.
+BASE_EXPORT void AppendSystemProfileAsTraceFormat(const SystemMetrics&
+                                                  system_stats,
+                                                  std::string* output);
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_TRACE_EVENT_SYSTEM_STATS_MONITOR_H_