[Courgette] Initial Implementation of LabelManager.

courgette/label_manager.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 COURGETTE_LABEL_MANAGER_H_
+#define COURGETTE_LABEL_MANAGER_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "courgette/image_utils.h"
+
+namespace courgette {
+
+// A container to store and manage Label instances. A key consideration is peak
+// memory usage reduction. To this end we preallocate Label instances in bulk,
+// and carefully control transient memory usage when initializing Labels.
+class LabelManager {
+ public:
+  // An adaptor to sequentially traverse multiple RVAs. This is useful for RVA
+  // translation without extra storage. For example, we might have a stored list
+  // of RVA locations, but we want to traverse the matching RVA targets.
+  class RvaVisitor {
+   public:
+    virtual ~RvaVisitor();
+
+    // Returns the number of remaining RVAs to visit.
+    virtual size_t Remaining() const = 0;
+
+    // Returns the current RVA.
+    virtual const RVA& Get() const = 0;

[grt (UTC plus 2), 2015/12/03 15:19:09]

an RVA is a 32-bit int, so treat it as a value type:
    virtual RVA Get() const = 0;

[huangs, 2015/12/03 19:29:06]

Done.

+
+    // Advances to the next RVA.
+    virtual void Next() = 0;
+  };
+
+  LabelManager();
+

[grt (UTC plus 2), 2015/12/03 15:19:09]

omit this newline

[huangs, 2015/12/03 19:29:06]

Done.

+  virtual ~LabelManager();
+
+  // Initializes |labels_| using RVAs from |rva_visitor|. Each distinct RVA from
+  // |rva_visitor| yields a Label with |rva_| assigned as the RVA, and |count_|
+  // assigned as the repeat.
+  void Read(RvaVisitor* rva_visitor);

[grt (UTC plus 2), 2015/12/03 15:19:09]

it's hard to review this without seeing the consumer of this function. is
implementing RvaVisitor easier than changing this function to:
  // Initializes the set of labels with the RVAs in |rvas| (ownership
  // of which is taken by this function).
  void Initialize(scoped_ptr<std::vector<RVA>> rvas);
and moving the "Write all values in |rva_visitor| to |rvas|." part of Read()
into the caller?

[huangs, 2015/12/03 19:29:06]

The plan is that RvaVisitor will be specialized over {different architectures} x
{Abs32, Rel32}.  If we just make this a pure RVA translator, we'd miss out some
optimizations that can be done with knowledge that Abs32 / Rel32 are sorted by
address (e.g., for Win32 PE, Abs32 target lookup can have a "current section"
state, without needing to loop over sections).  And since we'd have
differentiated code for looping, we may as well pass a visitor (iterator?
generator?), and let LabelManager worry about algorithm & temp variable details.

+
+  // Removes |labels_| elements whose |count_| is less than |count_threshold|.
+  void RemoveUnderusedLabels(int count_threshold);
+
+  // Efficiently searches for a Label that targets |rva|. Returns the pointer to
+  // the stored Label instance if found, or null otherwise.
+  Label* Find(RVA rva);
+
+  // TODO(huangs): Move AssignRemainingIndexes() here.
+
+ protected:
+  // The main list of Label instances, sorted by the |rva_| member.
+  std::vector<Label> labels_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LabelManager);
+};
+
+}  // namespace courgette
+
+#endif  // COURGETTE_LABEL_MANAGER_H_