1 files changed, 136 insertions, 0 deletions
diff --git a/src/common/DecayCounter.h b/src/common/DecayCounter.h
new file mode 100644
index 000000000..9455ecc5a
--- /dev/null
+++ b/src/common/DecayCounter.h
@@ -0,0 +1,136 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software 
+ * Foundation.  See file COPYING.
+ * 
+ */
+
+#ifndef CEPH_DECAYCOUNTER_H
+#define CEPH_DECAYCOUNTER_H
+
+#include "include/buffer.h"
+#include "common/Formatter.h"
+#include "common/StackStringStream.h"
+#include "common/ceph_time.h"
+
+#include <cmath>
+#include <list>
+#include <sstream>
+
+/**
+ *
+ * TODO: normalize value based on some function of half_life, 
+ *  so that it can be interpreted as an approximation of a
+ *  moving average of N seconds.  currently, changing half-life
+ *  skews the scale of the value, even at steady state.  
+ *
+ */
+
+class DecayRate {
+public:
+  friend class DecayCounter;
+
+  DecayRate() {}
+  // cppcheck-suppress noExplicitConstructor
+  DecayRate(double hl) { set_halflife(hl); }
+  DecayRate(const DecayRate &dr) : k(dr.k) {}
+
+  void set_halflife(double hl) {
+    k = log(.5) / hl;
+  }
+  double get_halflife() const {
+    return log(.5) / k;
+  }
+
+private:
+  double k = 0;             // k = ln(.5)/half_life
+};
+
+class DecayCounter {
+public:
+  using time = ceph::coarse_mono_time;
+  using clock = ceph::coarse_mono_clock;
+
+  DecayCounter() : DecayCounter(DecayRate()) {}
+  explicit DecayCounter(const DecayRate &rate) : last_decay(clock::now()), rate(rate) {}
+
+  void encode(ceph::buffer::list& bl) const;
+  void decode(ceph::buffer::list::const_iterator& p);
+  void dump(ceph::Formatter *f) const;
+  static void generate_test_instances(std::list<DecayCounter*>& ls);
+
+  /**
+   * reading
+   */
+
+  double get() const {
+    decay();
+    return val;
+  }
+
+  double get_last() const {
+    return val;
+  }
+  
+  time get_last_decay() const {
+    return last_decay; 
+  }
+
+  /**
+   * adjusting
+   */
+
+  double hit(double v = 1.0) {
+    decay(v);
+    return val;
+  }
+  void adjust(double v = 1.0) {
+    decay(v);
+  }
+
+  void scale(double f) {
+    val *= f;
+  }
+
+  /**
+   * decay etc.
+   */
+
+  void reset() {
+    last_decay = clock::now();
+    val = 0;
+  }
+
+protected:
+  void decay(double delta) const;
+  void decay() const {decay(0.0);}
+
+private:
+  mutable double val = 0.0;           // value
+  mutable time last_decay = clock::zero();   // time of last decay
+  DecayRate rate;
+};
+
+inline void encode(const DecayCounter &c, ceph::buffer::list &bl) {
+  c.encode(bl);
+}
+inline void decode(DecayCounter &c, ceph::buffer::list::const_iterator &p) {
+  c.decode(p);
+}
+
+inline std::ostream& operator<<(std::ostream& out, const DecayCounter& d) {
+  CachedStackStringStream css;
+  css->precision(2);
+  double val = d.get();
+  *css << "[C " << std::scientific << val << "]";
+  return out << css->strv();
+}
+
+#endif