Make task manager memory data more efficient and meaningful.

chrome/browser/private_working_set_snapshot.h

+// Copyright 2015 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 CHROME_BROWSER_PRIVATE_WORKING_SET_SNAPSHOT_H_
+#define CHROME_BROWSER_PRIVATE_WORKING_SET_SNAPSHOT_H_
+
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <pdh.h>
+
+#include <vector>
+
+#include "base/process/process_handle.h"
+#include "base/win/scoped_handle.h"
+
+namespace win {
+
+// The traits class for PDH handles that can be closed via PdhCloseQuery() API.
+struct PDHHandleTraits {
+  typedef PDH_HQUERY Handle;
+  static PDH_HQUERY NullHandle() { return nullptr; }
+  static bool IsHandleValid(PDH_HQUERY handle) { return handle != nullptr; }
+  static bool CloseHandle(PDH_HQUERY handle) {
+    return (PdhCloseQuery(handle) == ERROR_SUCCESS);
+  }
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(PDHHandleTraits);
+};
+
+// DummyVerifierTraits can be used because PDH_HQUERY is just a typedef for
+// HANDLE. However HandleTraits cannot be used because PdhCloseQuery must be
+// called rather than CloseHandle to dispose of the resources.
+typedef base::win::GenericScopedHandle<PDHHandleTraits,
+                                       base::win::DummyVerifierTraits>
+    ScopedPDH;

[ncarter (slow), 2015/07/01 16:50:26]

This could be a "using =" alias.

[brucedawson, 2015/07/01 17:47:40]

Done.

+
+}  // namespace win
+
+// This class can be used to do bulk collection of private working sets. This
+// exists because on Windows it is much faster to collect a group of private
+// working sets all at once using PdhOpenQuery than to calculate the private
+// working sets for each process individually.
+class PrivateWorkingSetSnapshot {
+ public:
+  PrivateWorkingSetSnapshot();
+  ~PrivateWorkingSetSnapshot();
+
+  // Add a process name that this object should monitor, such as "chrome". All
+  // processes whose name starts with this string will be monitored.
+  void AddToMonitorList(const std::string& process_name);
+
+  // Query the system for working-set information for all monitored processes
+  // and update the results cache. This function may take a few ms to run.
+  // The time it takes seems to be independent of the number of processes it
+  // retrieves data for. This makes it faster than using QueryWorkingSet as soon
+  // as the process count exceeds two or three.
+  void Sample();
+
+  // Ask for the working set for a specific process, from the most recent call
+  // to Sample. If no data is available then zero will be returned. The result
+  // is in bytes.
+  size_t GetPrivateWorkingSet(base::ProcessId process_id) const;
+
+ private:
+  // This holds a pair of Pdh counters to queries for the process ID and private
+  // working set for a particular process name being monitored. The results from
+  // the two queries can be matched up so that we can associate a private
+  // working set with a process ID.
+  struct PdhCounterPair {
+    // These are bound to query_handle_ and will be freed when it is closed.
+    // The handle to the 'counter' that retrieves process IDs.
+    PDH_HCOUNTER process_id_handle = nullptr;
+    // The handle to the 'counter' that retrieves private working sets.
+    PDH_HCOUNTER private_ws_handle = nullptr;
+  };
+
+  // Struct for storing a process ID and associated private working set.
+  struct PidAndPrivateWorkingSet {
+    base::ProcessId process_id;
+    size_t private_ws;
+    // Comparison function for sorting by process ID.
+    bool operator<(const PidAndPrivateWorkingSet& other) const {
+      return process_id < other.process_id;

[ncarter (slow), 2015/07/01 16:50:26]

I read the comment about "incomplete operator< impl" as saying that one usually
expects an operator< to on a pair-like struct to be lexicographic comparison
over the two data members.

At least 3 times in my career have I have seen bugs due to incorrectly
implemented lexicographic comparison on structs (when it's not a strict weak
ordering, quicksort does out-of-bounds reads), so seeing "operator<" is
something like a PTSD trigger for me, and as a result of that I do support
documenting that not looking at |private_ws| is what's actually intended. (We
all agree that the code is correct)

[brucedawson, 2015/07/01 17:47:40]

I'll add a comment to make that crystal clear. I think the CHECK/DCHECK would be
wrong but a comment to clarify intent is never a bad thing.

+    }
+    // Comparison function for searching.
+    bool operator<(const base::ProcessId other_process_id) const {
+      return process_id < other_process_id;
+    }
+  };
+
+  // The handle to the query object.
+  win::ScopedPDH query_handle_;
+
+  // A PdhCounterPair for each successful AddToMonitorList call.
+  std::vector<PdhCounterPair> counter_pairs_;
+
+  // After each call to Sample this will hold the results, sorted by process id.
+  std::vector<PidAndPrivateWorkingSet> records_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrivateWorkingSetSnapshot);
+};
+
+#endif  // defined(OS_WIN)
+
+#endif  // CHROME_BROWSER_PRIVATE_WORKING_SET_SNAPSHOT_H_