SL-18330: Review and tweak LLTrace::PeriodicRecording indexing

per Leviathan code review.

2 files changed, 105 insertions, 90 deletions

diff --git a/indra/llcommon/lltracerecording.cpp b/indra/llcommon/lltracerecording.cpp
index 5f16334c84..bb3d667a42 100644
--- a/indra/llcommon/lltracerecording.cpp
+++ b/indra/llcommon/lltracerecording.cpp
@@ -577,10 +577,12 @@ S32 Recording::getSampleCount( const StatType<EventAccumulator>& stat )
 // PeriodicRecording
 ///////////////////////////////////////////////////////////////////////
 
-PeriodicRecording::PeriodicRecording( S32 num_periods, EPlayState state) 
+PeriodicRecording::PeriodicRecording( size_t num_periods, EPlayState state) 
 :	mAutoResize(num_periods == 0),
 	mCurPeriod(0),
 	mNumRecordedPeriods(0),
+	// This guarantee that mRecordingPeriods cannot be empty is essential for
+	// code in several methods.
 	mRecordingPeriods(num_periods ? num_periods : 1)
 {
     LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
@@ -596,18 +598,19 @@ PeriodicRecording::~PeriodicRecording()
 
 void PeriodicRecording::nextPeriod()
 {
-    LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
+	LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
 	if (mAutoResize)
 	{
 		mRecordingPeriods.push_back(Recording());
 	}
 
 	Recording& old_recording = getCurRecording();
-	mCurPeriod = (mCurPeriod + 1) % mRecordingPeriods.size();
+	inci(mCurPeriod);
 	old_recording.splitTo(getCurRecording());
 
-	mNumRecordedPeriods = mRecordingPeriods.empty()? 0 :
-		llmin(mRecordingPeriods.size() - 1, mNumRecordedPeriods + 1);
+	// Since mRecordingPeriods always has at least one entry, we can always
+	// safely subtract 1 from its size().
+	mNumRecordedPeriods = llmin(mRecordingPeriods.size() - 1, mNumRecordedPeriods + 1);
 }
 
 void PeriodicRecording::appendRecording(Recording& recording)
@@ -620,31 +623,29 @@ void PeriodicRecording::appendRecording(Recording& recording)
 
 void PeriodicRecording::appendPeriodicRecording( PeriodicRecording& other )
 {
-    LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
+	LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
 	if (other.mRecordingPeriods.empty()) return;
 
 	getCurRecording().update();
 	other.getCurRecording().update();
-	
-	const auto other_recording_slots = other.mRecordingPeriods.size();
+
 	const auto other_num_recordings = other.getNumRecordedPeriods();
 	const auto other_current_recording_index = other.mCurPeriod;
-	const auto other_oldest_recording_index = (other_current_recording_index + other_recording_slots - other_num_recordings) % other_recording_slots;
+	const auto other_oldest_recording_index = other.previ(other_current_recording_index, other_num_recordings);
 
 	// append first recording into our current slot
 	getCurRecording().appendRecording(other.mRecordingPeriods[other_oldest_recording_index]);
 
 	// from now on, add new recordings for everything after the first
-	auto other_index = (other_oldest_recording_index + 1) % other_recording_slots;
+	auto other_index = other.nexti(other_oldest_recording_index);
 
 	if (mAutoResize)
 	{
 		// push back recordings for everything in the middle
-		auto other_index = (other_oldest_recording_index + 1) % other_recording_slots;
 		while (other_index != other_current_recording_index)
 		{
 			mRecordingPeriods.push_back(other.mRecordingPeriods[other_index]);
-			other_index = (other_index + 1) % other_recording_slots;
+			other.inci(other_index);
 		}
 
 		// add final recording, if it wasn't already added as the first
@@ -653,36 +654,25 @@ void PeriodicRecording::appendPeriodicRecording( PeriodicRecording& other )
 			mRecordingPeriods.push_back(other.mRecordingPeriods[other_current_recording_index]);
 		}
 
-		mCurPeriod = mRecordingPeriods.empty()? 0 : mRecordingPeriods.size() - 1;
+		// mRecordingPeriods is never empty()
+		mCurPeriod = mRecordingPeriods.size() - 1;
 		mNumRecordedPeriods = mCurPeriod;
 	}
 	else
 	{
-		S32 num_to_copy = llmin((S32)mRecordingPeriods.size(), (S32)other_num_recordings);
-
-		std::vector<Recording>::iterator src_it = other.mRecordingPeriods.begin() + other_index ;
-		std::vector<Recording>::iterator dest_it = mRecordingPeriods.begin() + mCurPeriod;
-
+		auto num_to_copy = llmin(mRecordingPeriods.size(), other_num_recordings);
 		// already consumed the first recording from other, so start counting at 1
-		for(S32 i = 1; i < num_to_copy; i++)
+		for (size_t n = 1, srci = other_index, dsti = mCurPeriod;
+			 n < num_to_copy;
+			 ++n, other.inci(srci), inci(dsti))
 		{
-			*dest_it = *src_it;
-
-			if (++src_it == other.mRecordingPeriods.end())
-			{
-				src_it = other.mRecordingPeriods.begin();
-			}
-
-			if (++dest_it == mRecordingPeriods.end())
-			{
-				dest_it = mRecordingPeriods.begin();
-			}
+			mRecordingPeriods[dsti] = other.mRecordingPeriods[srci];
 		}
-		
+
 		// want argument to % to be positive, otherwise result could be negative and thus out of bounds
 		llassert(num_to_copy >= 1);
 		// advance to last recording period copied, and make that our current period
-		mCurPeriod = (mCurPeriod + num_to_copy - 1) % mRecordingPeriods.size();
+		inci(mCurPeriod, num_to_copy - 1);
 		mNumRecordedPeriods = llmin(mRecordingPeriods.size() - 1, mNumRecordedPeriods + num_to_copy - 1);
 	}
 
@@ -694,13 +684,11 @@ void PeriodicRecording::appendPeriodicRecording( PeriodicRecording& other )
 
 F64Seconds PeriodicRecording::getDuration() const
 {
-    LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
+	LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
 	F64Seconds duration;
-	auto num_periods = mRecordingPeriods.size();
-	for (size_t i = 1; i <= num_periods; i++)
+	for (size_t n = 0; n < mRecordingPeriods.size(); ++n)
 	{
-		auto index = (mCurPeriod + num_periods - i) % num_periods;
-		duration += mRecordingPeriods[index].getDuration();
+		duration += mRecordingPeriods[nexti(mCurPeriod, n)].getDuration();
 	}
 	return duration;
 }
@@ -737,16 +725,14 @@ const Recording& PeriodicRecording::getCurRecording() const
 
 Recording& PeriodicRecording::getPrevRecording( size_t offset )
 {
-	auto num_periods = mRecordingPeriods.size();
-	offset = llclamp(offset, 0, num_periods - 1);
-	return mRecordingPeriods[(mCurPeriod + num_periods - offset) % num_periods];
+	// reuse const implementation, but return non-const reference
+	return const_cast<Recording&>(
+		const_cast<const PeriodicRecording*>(this)->getPrevRecording(offset));
 }
 
 const Recording& PeriodicRecording::getPrevRecording( size_t offset ) const
 {
-	auto num_periods = mRecordingPeriods.size();
-	offset = llclamp(offset, 0, num_periods - 1);
-	return mRecordingPeriods[(mCurPeriod + num_periods - offset) % num_periods];
+	return mRecordingPeriods[previ(mCurPeriod, offset)];
 }
 
 void PeriodicRecording::handleStart()
@@ -796,7 +782,7 @@ F64 PeriodicRecording::getPeriodMin( const StatType<EventAccumulator>& stat, siz
 
 	bool has_value = false;
 	F64 min_val = std::numeric_limits<F64>::max();
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -818,7 +804,7 @@ F64 PeriodicRecording::getPeriodMax( const StatType<EventAccumulator>& stat, siz
 
 	bool has_value = false;
 	F64 max_val = std::numeric_limits<F64>::min();
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -842,7 +828,7 @@ F64 PeriodicRecording::getPeriodMean( const StatType<EventAccumulator>& stat, si
 	F64 mean = 0;
 	S32 valid_period_count = 0;
 
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -866,7 +852,7 @@ F64 PeriodicRecording::getPeriodStandardDeviation( const StatType<EventAccumulat
 	F64 sum_of_squares = 0;
 	S32 valid_period_count = 0;
 
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -889,7 +875,7 @@ F64 PeriodicRecording::getPeriodMin( const StatType<SampleAccumulator>& stat, si
 
 	bool has_value = false;
 	F64 min_val = std::numeric_limits<F64>::max();
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -911,7 +897,7 @@ F64 PeriodicRecording::getPeriodMax(const StatType<SampleAccumulator>& stat, siz
 
 	bool has_value = false;
 	F64 max_val = std::numeric_limits<F64>::min();
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -935,7 +921,7 @@ F64 PeriodicRecording::getPeriodMean( const StatType<SampleAccumulator>& stat, s
 	S32 valid_period_count = 0;
 	F64 mean = 0;
 
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -956,7 +942,7 @@ F64 PeriodicRecording::getPeriodMedian( const StatType<SampleAccumulator>& stat,
 	num_periods = llmin(num_periods, getNumRecordedPeriods());
 
 	std::vector<F64> buf;
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.getDuration() > (F32Seconds)0.f)
@@ -985,7 +971,7 @@ F64 PeriodicRecording::getPeriodStandardDeviation( const StatType<SampleAccumula
 	S32 valid_period_count = 0;
 	F64 sum_of_squares = 0;
 
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
@@ -1008,7 +994,7 @@ F64Kilobytes PeriodicRecording::getPeriodMin( const StatType<MemAccumulator>& st
 	num_periods = llmin(num_periods, getNumRecordedPeriods());
 
 	F64Kilobytes min_val(std::numeric_limits<F64>::max());
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		min_val = llmin(min_val, recording.getMin(stat));
@@ -1028,7 +1014,7 @@ F64Kilobytes PeriodicRecording::getPeriodMax(const StatType<MemAccumulator>& sta
 	num_periods = llmin(num_periods, getNumRecordedPeriods());
 
 	F64Kilobytes max_val(0.0);
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		max_val = llmax(max_val, recording.getMax(stat));
@@ -1049,7 +1035,7 @@ F64Kilobytes PeriodicRecording::getPeriodMean( const StatType<MemAccumulator>& s
 
 	F64Kilobytes mean(0);
 
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		mean += recording.getMean(stat);
@@ -1072,7 +1058,7 @@ F64Kilobytes PeriodicRecording::getPeriodStandardDeviation( const StatType<MemAc
 	S32 valid_period_count = 0;
 	F64 sum_of_squares = 0;
 
-	for (S32 i = 1; i <= num_periods; i++)
+	for (size_t i = 1; i <= num_periods; i++)
 	{
 		Recording& recording = getPrevRecording(i);
 		if (recording.hasValue(stat))
diff --git a/indra/llcommon/lltracerecording.h b/indra/llcommon/lltracerecording.h
index 66cee59764..a6b1a67d02 100644
--- a/indra/llcommon/lltracerecording.h
+++ b/indra/llcommon/lltracerecording.h
@@ -331,7 +331,7 @@ namespace LLTrace
 	:	public LLStopWatchControlsMixin<PeriodicRecording>
 	{
 	public:
-		PeriodicRecording(S32 num_periods, EPlayState state = STOPPED);
+		PeriodicRecording(size_t num_periods, EPlayState state = STOPPED);
 		~PeriodicRecording();
 
 		void nextPeriod();
@@ -381,7 +381,7 @@ namespace LLTrace
 
 			bool has_value = false;
 			typename T::value_t min_val(std::numeric_limits<typename T::value_t>::max());
-			for (S32 i = 1; i <= num_periods; i++)
+			for (size_t i = 1; i <= num_periods; i++)
 			{
 				Recording& recording = getPrevRecording(i);
 				if (recording.hasValue(stat))
@@ -429,7 +429,7 @@ namespace LLTrace
 			num_periods = llmin(num_periods, getNumRecordedPeriods());
 
 			typename RelatedTypes<typename T::value_t>::fractional_t min_val(std::numeric_limits<F64>::max());
-			for (S32 i = 1; i <= num_periods; i++)
+			for (size_t i = 1; i <= num_periods; i++)
 			{
 				Recording& recording = getPrevRecording(i);
 				min_val = llmin(min_val, recording.getPerSec(stat));
@@ -457,7 +457,7 @@ namespace LLTrace
 
 			bool has_value = false;
 			typename T::value_t max_val(std::numeric_limits<typename T::value_t>::min());
-			for (S32 i = 1; i <= num_periods; i++)
+			for (size_t i = 1; i <= num_periods; i++)
 			{
 				Recording& recording = getPrevRecording(i);
 				if (recording.hasValue(stat))
@@ -505,7 +505,7 @@ namespace LLTrace
 			num_periods = llmin(num_periods, getNumRecordedPeriods());
 
 			F64 max_val = std::numeric_limits<F64>::min();
-			for (S32 i = 1; i <= num_periods; i++)
+			for (size_t i = 1; i <= num_periods; i++)
 			{
 				Recording& recording = getPrevRecording(i);
 				max_val = llmax(max_val, recording.getPerSec(stat));
@@ -533,7 +533,7 @@ namespace LLTrace
 
 			typename RelatedTypes<typename T::value_t>::fractional_t mean(0);
 
-			for (S32 i = 1; i <= num_periods; i++)
+			for (size_t i = 1; i <= num_periods; i++)
 			{
 				Recording& recording = getPrevRecording(i);
 				if (recording.getDuration() > (F32Seconds)0.f)
@@ -579,7 +579,7 @@ namespace LLTrace
 
 			typename RelatedTypes<typename T::value_t>::fractional_t mean = 0;
 
-			for (S32 i = 1; i <= num_periods; i++)
+			for (size_t i = 1; i <= num_periods; i++)
 			{
 				Recording& recording = getPrevRecording(i);
 				if (recording.getDuration() > (F32Seconds)0.f)
@@ -600,34 +600,34 @@ namespace LLTrace
 			return typename RelatedTypes<T>::fractional_t(getPeriodMeanPerSec(static_cast<const StatType<CountAccumulator>&>(stat), num_periods));
 		}
 
-        F64 getPeriodMedian( const StatType<SampleAccumulator>& stat, size_t num_periods = std::numeric_limits<size_t>::max());
+		F64 getPeriodMedian( const StatType<SampleAccumulator>& stat, size_t num_periods = std::numeric_limits<size_t>::max());
 
-        template <typename T>
-        typename RelatedTypes<typename T::value_t>::fractional_t getPeriodMedianPerSec(const StatType<T>& stat, size_t num_periods = std::numeric_limits<size_t>::max())
-        {
-            LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
-            num_periods = llmin(num_periods, getNumRecordedPeriods());
-
-            std::vector <typename RelatedTypes<typename T::value_t>::fractional_t> buf;
-            for (S32 i = 1; i <= num_periods; i++)
-            {
-                Recording& recording = getPrevRecording(i);
-                if (recording.getDuration() > (F32Seconds)0.f)
-                {
-                    buf.push_back(recording.getPerSec(stat));
-                }
-            }
-            std::sort(buf.begin(), buf.end());
-
-            return typename RelatedTypes<T>::fractional_t((buf.size() % 2 == 0) ? (buf[buf.size() / 2 - 1] + buf[buf.size() / 2]) / 2 : buf[buf.size() / 2]);
-        }
-
-        template<typename T>
-        typename RelatedTypes<T>::fractional_t getPeriodMedianPerSec(const CountStatHandle<T>& stat, size_t num_periods = std::numeric_limits<size_t>::max())
-        {
-            LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
-            return typename RelatedTypes<T>::fractional_t(getPeriodMedianPerSec(static_cast<const StatType<CountAccumulator>&>(stat), num_periods));
-        }
+		template <typename T>
+		typename RelatedTypes<typename T::value_t>::fractional_t getPeriodMedianPerSec(const StatType<T>& stat, size_t num_periods = std::numeric_limits<size_t>::max())
+		{
+			LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
+			num_periods = llmin(num_periods, getNumRecordedPeriods());
+
+			std::vector <typename RelatedTypes<typename T::value_t>::fractional_t> buf;
+			for (size_t i = 1; i <= num_periods; i++)
+			{
+				Recording& recording = getPrevRecording(i);
+				if (recording.getDuration() > (F32Seconds)0.f)
+				{
+					buf.push_back(recording.getPerSec(stat));
+				}
+			}
+			std::sort(buf.begin(), buf.end());
+
+			return typename RelatedTypes<T>::fractional_t((buf.size() % 2 == 0) ? (buf[buf.size() / 2 - 1] + buf[buf.size() / 2]) / 2 : buf[buf.size() / 2]);
+		}
+
+		template<typename T>
+		typename RelatedTypes<T>::fractional_t getPeriodMedianPerSec(const CountStatHandle<T>& stat, size_t num_periods = std::numeric_limits<size_t>::max())
+		{
+			LL_PROFILE_ZONE_SCOPED_CATEGORY_STATS;
+			return typename RelatedTypes<T>::fractional_t(getPeriodMedianPerSec(static_cast<const StatType<CountAccumulator>&>(stat), num_periods));
+		}
 
 		//
 		// PERIODIC STANDARD DEVIATION
@@ -660,6 +660,35 @@ namespace LLTrace
 		/*virtual*/ void handleReset();
 		/*virtual*/ void handleSplitTo(PeriodicRecording& other);
 
+		// helper methods for wraparound ring-buffer arithmetic
+		inline
+		size_t wrapi(size_t i) const
+		{
+			return i % mRecordingPeriods.size();
+		}
+
+		inline
+		size_t nexti(size_t i, size_t offset=1) const
+		{
+			return wrapi(i + offset);
+		}
+
+		inline
+		size_t previ(size_t i, size_t offset=1) const
+		{
+			auto num_periods = mRecordingPeriods.size();
+			// constrain offset
+			offset = llclamp(offset, 0, num_periods - 1);
+			// add size() so expression can't go (unsigned) "negative"
+			return wrapi(i + num_periods - offset);
+		}
+
+		inline
+		void inci(size_t& i, size_t offset=1) const
+		{
+			i = nexti(i, offset);
+		}
+
 	private:
 		std::vector<Recording>	mRecordingPeriods;
 		const bool				mAutoResize;