core: tune performance (#73)

- Avoid using recursive function in critical path.
- Do not write through when using levelDB. Things put to
   levelDB would be safe from panic even we didn't force
   to write through every time.
- Dump count of confirmed blocks proposed by self.
- Avoid allocating variables in loop.
- Return length of acking node set, we only need that
   when total ordering.
- Fix potential bug: make sure win records updated when
   acking height vectors of candidates are changed.
- Keep dirty validators in slice.
- Add cache for objects to ease the pressure to garbage
   collector.
- Cache global acking status when total ordering.
- Add method to recycle blocks.
- Marshal JSON should be called once for each broadcast.
- Make updateWinRecord called in parallel.
- Log average / deviation of latencies when simulation
   finished.

1 files changed, 26 insertions, 0 deletions

diff --git a/core/test/utils.go b/core/test/utils.go
index 35fbdd5..789c28e 100644
--- a/core/test/utils.go
+++ b/core/test/utils.go
@@ -18,6 +18,9 @@
 package test
 
 import (
+	"math"
+	"time"
+
 	"github.com/dexon-foundation/dexon-consensus-core/common"
 	"github.com/dexon-foundation/dexon-consensus-core/core/types"
 )
@@ -38,3 +41,26 @@ func GenerateRandomValidatorIDs(validatorCount int) (vIDs types.ValidatorIDs) {
 	}
 	return
 }
+
+// CalcLatencyStatistics calculates average and deviation from a slice
+// of latencies.
+func CalcLatencyStatistics(latencies []time.Duration) (avg, dev time.Duration) {
+	var (
+		sum             float64
+		sumOfSquareDiff float64
+	)
+
+	// Calculate average.
+	for _, v := range latencies {
+		sum += float64(v)
+	}
+	avgAsFloat := sum / float64(len(latencies))
+	avg = time.Duration(avgAsFloat)
+	// Calculate deviation
+	for _, v := range latencies {
+		diff := math.Abs(float64(v) - avgAsFloat)
+		sumOfSquareDiff += diff * diff
+	}
+	dev = time.Duration(math.Sqrt(sumOfSquareDiff / float64(len(latencies)-1)))
+	return
+}