1 files changed, 139 insertions, 0 deletions
diff --git a/xpcom/threads/PerformanceCounter.h b/xpcom/threads/PerformanceCounter.h
new file mode 100644
index 0000000000..4181320e10
--- /dev/null
+++ b/xpcom/threads/PerformanceCounter.h
@@ -0,0 +1,139 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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_PerformanceCounter_h
+#define mozilla_PerformanceCounter_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/TaskCategory.h"
+#include "nsISupportsImpl.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+/*
+ * The DispatchCategory class is used to fake the inheritance
+ * of the TaskCategory enum so we can extend it to hold
+ * one more value corresponding to the category
+ * we use when a worker dispatches a call.
+ *
+ */
+class DispatchCategory final {
+ public:
+  explicit DispatchCategory(uint32_t aValue) : mValue(aValue) {
+    // Since DispatchCategory is adding one single value to the
+    // TaskCategory enum, we can check here that the value is
+    // the next index e.g. TaskCategory::Count
+    MOZ_ASSERT(aValue == (uint32_t)TaskCategory::Count);
+  }
+
+  constexpr explicit DispatchCategory(TaskCategory aValue)
+      : mValue((uint32_t)aValue) {}
+
+  uint32_t GetValue() const { return mValue; }
+
+  static const DispatchCategory Worker;
+
+ private:
+  uint32_t mValue;
+};
+
+typedef Array<Atomic<uint32_t>, (uint32_t)TaskCategory::Count + 1>
+    DispatchCounter;
+
+// PerformanceCounter is a class that can be used to keep track of
+// runnable execution times and dispatch counts.
+//
+// - runnable execution time: time spent in a runnable when called
+//   in nsThread::ProcessNextEvent (not counting recursive calls)
+// - dispatch counts: number of times a tracked runnable is dispatched
+//   in nsThread. Useful to measure the activity of a tab or worker.
+//
+// The PerformanceCounter class is currently instantiated in DocGroup
+// and WorkerPrivate in order to count how many scheduler dispatches
+// are done through them, and how long the execution lasts.
+//
+// The execution time is calculated by the nsThread class (and its
+// inherited WorkerThread class) in its ProcessNextEvent method.
+//
+// For each processed runnable, nsThread will reach out the
+// PerformanceCounter attached to the runnable via its DocGroup
+// or WorkerPrivate and call IncrementExecutionDuration()
+//
+// Notice that the execution duration counting takes into account
+// recursivity. If an event triggers a recursive call to
+// nsThread::ProcessNextEVent, the counter will discard the time
+// spent in sub events.
+class PerformanceCounter final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(PerformanceCounter)
+
+  explicit PerformanceCounter(const nsACString& aName);
+
+  /**
+   * This is called everytime a runnable is dispatched.
+   *
+   * aCategory can be used to distinguish counts per TaskCategory
+   *
+   * Note that an overflow will simply reset the counter.
+   */
+  void IncrementDispatchCounter(DispatchCategory aCategory);
+
+  /**
+   * This is called via nsThread::ProcessNextEvent to measure runnable
+   * execution duration.
+   *
+   * Note that an overflow will simply reset the counter.
+   */
+  void IncrementExecutionDuration(uint32_t aMicroseconds);
+
+  /**
+   * Returns a category/counter array of all dispatches.
+   */
+  const DispatchCounter& GetDispatchCounter() const;
+
+  /**
+   * Returns the total execution duration.
+   */
+  uint64_t GetExecutionDuration() const;
+
+  /**
+   * Returns the number of dispatches per TaskCategory.
+   */
+  uint32_t GetDispatchCount(DispatchCategory aCategory) const;
+
+  /**
+   * Returns the total number of dispatches.
+   */
+  uint64_t GetTotalDispatchCount() const;
+
+  /**
+   * Returns the unique id for the instance.
+   *
+   * Used to distinguish instances since the lifespan of
+   * a PerformanceCounter can be shorter than the
+   * host it's tracking. That leads to edge cases
+   * where a counter appears to have values that go
+   * backwards. Having this id let the consumers
+   * detect that they are dealing with a new counter
+   * when it happens.
+   */
+  uint64_t GetID() const;
+
+ private:
+  ~PerformanceCounter() = default;
+
+  Atomic<uint64_t> mExecutionDuration;
+  Atomic<uint64_t> mTotalDispatchCount;
+  DispatchCounter mDispatchCounter;
+  nsCString mName;
+  const uint64_t mID;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_PerformanceCounter_h