Windows-native sampling profiler wrapper class.

base/win/sampling_profiler.h

Index: base/win/sampling_profiler.h
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+// Copyright (c) 2011 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_WIN_SAMPLING_PROFILER_H_
+#define BASE_WIN_SAMPLING_PROFILER_H_
+#pragma once
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/time.h"
+#include "base/win/scoped_handle.h"
+
+namespace base {
+namespace win {
+
+// This class exposes the functionality of Window's built-in sampling profiler.
+// Each profiler instance covers a range of memory, and while the profiler is
+// running, its buckets will count the number of times the instruction counter
+// lands in the associated range of memory on a sample.
+// The sampling interval is settable, but the setting is system-wide.
+class BASE_EXPORT SamplingProfiler {
+ public:
+  // Create an uninitialized sampling profiler.
+  SamplingProfiler();
+  ~SamplingProfiler();
+
+  // Initializes the profiler to cover the memory range |start| through
+  // |start| + |size|, in the process |process_handle| with bucket size
+  // |2^log2_bucket_size|, |log2_bucket_size| must be in the range 2-31,
+  // for bucket sizes of 4 bytes to 2 gigabytes.
+  // The process handle must grant at least PROCESS_QUERY_INFORMATION.
+  // The memory range should be exectuable code, like e.g. the text segment
+  // of an exectuable (whether DLL or EXE).
+  // Returns true on success.
+  bool Initialize(HANDLE process_handle,
+                  void* start,
+                  size_t size,
+                  size_t log2_bucket_size);
+
+  // Start this profiler, which must be initialized and not started.
+  bool Start();

[M-A Ruel, 2011/12/06 15:02:50]

For functions like that, I always ask myself: is the return value really useful?
Can the client do anything about it or should it care?

Personally I'd prefer silent failure for these kinds of things, since it's not a
fatal failure and the app can't do much about it. So Stop() could be called even
if Start() failed. The client shouldn't care about it.

But I don't really mind so ignore the comment above. :)

[Sigurður Ásgeirsson, 2011/12/06 16:12:08]

That's good comment. I started changing the interface, but then that leaves me
with a CHECK, as if a profile can't be stopped, you'll end up with a random
memory overwrite in the future as the vector is freed ...
I'm pretty sure stopping a profile will never fail, so maybe this is a
non-issue...

+  // Stop this profiler, which must be started.
+  bool Stop();
+
+  // Get and set the sampling interval.
+  // Note that this is a system-wide setting.
+  static bool SetSamplingInterval(base::TimeDelta sampling_interval);
+  static bool GetSamplingInterval(base::TimeDelta* sampling_interval);
+
+  // Accessors.
+  bool is_started() const { return is_started_; }
+
+  // It is safe to read the counts in the sampling buckets at any time.
+  // Note however that there's no guarantee that you'll read consistent counts
+  // until the profiler has been stopped, as the counts may be updating on other
+  // CPU cores.
+  const std::vector<ULONG>& buckets() const { return buckets_; }
+
+ private:
+  // Handle to the corresponding kernel object.
+  ScopedHandle profile_handle_;
+  // True iff this profiler is started.
+  bool is_started_;
+  std::vector<ULONG> buckets_;
+
+  DISALLOW_COPY_AND_ASSIGN(SamplingProfiler);
+};
+
+}  // namespace win
+}  // namespace base
+
+#endif  // BASE_WIN_SAMPLING_PROFILER_H_