diff -r 000000000000 -r 6474c204b198 toolkit/components/telemetry/ThreadHangStats.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/telemetry/ThreadHangStats.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,113 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_BackgroundHangTelemetry_h
+#define mozilla_BackgroundHangTelemetry_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Move.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/Vector.h"
+
+#include "nsString.h"
+#include "prinrval.h"
+
+namespace mozilla {
+namespace Telemetry {
+
+static const size_t kTimeHistogramBuckets = 8 * sizeof(PRIntervalTime);
+
+/* TimeHistogram is an efficient histogram that puts time durations into
+   exponential (base 2) buckets; times are accepted in PRIntervalTime and
+   stored in milliseconds. */
+class TimeHistogram : public mozilla::Array<uint32_t, kTimeHistogramBuckets>
+{
+public:
+  TimeHistogram()
+  {
+    mozilla::PodArrayZero(*this);
+  }
+  // Get minimum (inclusive) range of bucket in milliseconds
+  uint32_t GetBucketMin(size_t aBucket) const {
+    MOZ_ASSERT(aBucket < ArrayLength(*this));
+    return (1u << aBucket) & ~1u; // Bucket 0 starts at 0, not 1
+  }
+  // Get maximum (inclusive) range of bucket in milliseconds
+  uint32_t GetBucketMax(size_t aBucket) const {
+    MOZ_ASSERT(aBucket < ArrayLength(*this));
+    return (1u << (aBucket + 1u)) - 1u;
+  }
+  void Add(PRIntervalTime aTime);
+};
+
+/* A hang histogram consists of a stack associated with the
+   hang, along with a time histogram of the hang times. */
+class HangHistogram : public TimeHistogram
+{
+public:
+  typedef mozilla::Vector<const char*, 8> Stack;
+
+private:
+  static uint32_t GetHash(const Stack& aStack);
+
+  Stack mStack;
+  // Use a hash to speed comparisons
+  const uint32_t mHash;
+
+public:
+  explicit HangHistogram(Stack&& aStack)
+    : mStack(mozilla::Move(aStack))
+    , mHash(GetHash(mStack))
+  {
+  }
+  HangHistogram(HangHistogram&& aOther)
+    : TimeHistogram(mozilla::Move(aOther))
+    , mStack(mozilla::Move(aOther.mStack))
+    , mHash(mozilla::Move(aOther.mHash))
+  {
+  }
+  bool operator==(const HangHistogram& aOther) const;
+  bool operator!=(const HangHistogram& aOther) const
+  {
+    return !operator==(aOther);
+  }
+  const Stack& GetStack() const {
+    return mStack;
+  }
+};
+
+/* Thread hang stats consist of
+ - thread name
+ - time histogram of all task run times
+ - hang histograms of individual hangs. */
+class ThreadHangStats
+{
+private:
+  nsAutoCString mName;
+
+public:
+  TimeHistogram mActivity;
+  mozilla::Vector<HangHistogram, 4> mHangs;
+
+  explicit ThreadHangStats(const char* aName)
+    : mName(aName)
+  {
+  }
+  ThreadHangStats(ThreadHangStats&& aOther)
+    : mName(mozilla::Move(aOther.mName))
+    , mActivity(mozilla::Move(aOther.mActivity))
+    , mHangs(mozilla::Move(aOther.mHangs))
+  {
+  }
+  const char* GetName() const {
+    return mName.get();
+  }
+};
+
+} // namespace Telemetry
+} // namespace mozilla
+#endif // mozilla_BackgroundHangTelemetry_h