1 files changed, 67 insertions, 0 deletions
diff --git a/metricsd/persistent_integer.h b/metricsd/persistent_integer.h
new file mode 100644
index 000000000..b1cfcf4ef
--- /dev/null
+++ b/metricsd/persistent_integer.h
@@ -0,0 +1,67 @@
+// Copyright (c) 2014 The Chromium OS 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 METRICS_PERSISTENT_INTEGER_H_
+#define METRICS_PERSISTENT_INTEGER_H_
+
+#include <stdint.h>
+
+#include <string>
+
+namespace chromeos_metrics {
+
+// PersistentIntegers is a named 64-bit integer value backed by a file.
+// The in-memory value acts as a write-through cache of the file value.
+// If the backing file doesn't exist or has bad content, the value is 0.
+
+class PersistentInteger {
+ public:
+  explicit PersistentInteger(const std::string& name);
+
+  // Virtual only because of mock.
+  virtual ~PersistentInteger();
+
+  // Sets the value.  This writes through to the backing file.
+  void Set(int64_t v);
+
+  // Gets the value.  May sync from backing file first.
+  int64_t Get();
+
+  // Returns the name of the object.
+  std::string Name() { return name_; }
+
+  // Convenience function for Get() followed by Set(0).
+  int64_t GetAndClear();
+
+  // Convenience function for v = Get, Set(v + x).
+  // Virtual only because of mock.
+  virtual void Add(int64_t x);
+
+  // After calling with |testing| = true, changes some behavior for the purpose
+  // of testing.  For instance: instances created while testing use the current
+  // directory for the backing files.
+  static void SetTestingMode(bool testing);
+
+ private:
+  static const int kVersion = 1001;
+
+  // Writes |value_| to the backing file, creating it if necessary.
+  void Write();
+
+  // Reads the value from the backing file, stores it in |value_|, and returns
+  // true if the backing file is valid.  Returns false otherwise, and creates
+  // a valid backing file as a side effect.
+  bool Read();
+
+  int64_t value_;
+  int32_t version_;
+  std::string name_;
+  std::string backing_file_name_;
+  bool synced_;
+  static bool testing_;
+};
+
+}  // namespace chromeos_metrics
+
+#endif  // METRICS_PERSISTENT_INTEGER_H_