[Chromoting] Retrieve process resource usage (ProcessStats) and its tests

remoting/host/host_stats.h

+// Copyright 2017 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 REMOTING_HOST_HOST_STATS_H_
+#define REMOTING_HOST_HOST_STATS_H_
+
+#include <memory>
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/process/process_metrics.h"
+#include "base/synchronization/lock.h"
+#include "base/task_runner.h"
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "remoting/base/process_resource_usage.h"
+#include "remoting/host/host_stats_stub.h"
+
+namespace remoting {
+namespace host {
+
+// A component to report host process statistic data regularly. This class also
+// implements HostStatsStub, so several HostStats instances can chain together
+// to accumulate the total resource usage of several processes.

[Sergey Ulanov, 2017/03/27 19:43:20]

I don't think that chaining is the best approach here. It's not intuitive and 
now scheduling and multiplexing logic is mixed with the core. What happens if
interval passed to these objects is different. It also makes destruction harder.
How about a simple class that holds multiple HostStats sources and multiplexes
the stats it gets from them. I would also prefer that object to be responsible
for scheduling.

[Hzj_jie, 2017/03/30 01:09:45]

I have no objection on holding several HostStats sources in a different class.
But since the process metrics of another process are always coming from IPC
channel, we always cannot assume the intervals of two HostStats are the same. So
the received_usage_ is always the latest states.

+class HostStats final : public HostStatsStub {

[Sergey Ulanov, 2017/03/27 19:43:20]

HostStatsSender or maybe HostStatsAgenet 

[Hzj_jie, 2017/03/30 01:09:46]

Done.

+ public:
+  // HostStats starts immediately, and reports the statistic data to
+  // |host_stats_stub| once per |interval| in
+  // MessageLoop::current()->task_runner(). HostStats does not take the
+  // ownership of |host_stats_stub|. It needs to be outlived this instance.
+  HostStats(HostStatsStub* host_stats_stub, base::TimeDelta interval);
+
+  // Needs to be destructed on the same thread as constructing.
+  ~HostStats();
+
+ private:
+  void PostTask();
+
+  void ReportUsage();
+
+  // HostStatsStub interface.
+  void OnHostStats(const ProcessResourceUsage& usage) override;
+
+  HostStatsStub* const host_stats_stub_;
+  const base::TimeDelta interval_;
+  const std::unique_ptr<base::ProcessMetrics> metrics_;
+  base::Lock lock_;
+  ProcessResourceUsage received_usage_;
+  base::WeakPtrFactory<HostStats> weak_factory_;
+};
+
+}  // namespace host
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_HOST_STATS_H_