added query cache

cache.go

@@ -0,0 +1,66 @@
+// Copyright (C) 2017 Marius Schellenberger
+
+package filter
+
+import (
+	"math/rand"
+	"sync"
+)
+
+// QueryCache can be used to cache queries
+type QueryCache struct {
+	// protects m
+	sync.RWMutex
+
+	m   map[string]Query
+	max int
+}
+
+// NewQueryCache returns a new QueryCache
+func NewQueryCache(max int) *QueryCache {
+	return &QueryCache{
+		m:   make(map[string]Query),
+		max: max,
+	}
+}
+
+// NewQuery looks for the given query in the cache and returns it.
+// If the query is not found it will be generated and inserted in the cache..
+func (qc *QueryCache) NewQuery(s string) (q *Query, err error) {
+	q = qc.lookup(s)
+	if q != nil {
+		return
+	}
+	q, err = NewQuery(s)
+	if err != nil {
+		return
+	}
+	qc.Lock()
+	defer qc.Unlock()
+	if len(qc.m) == qc.max {
+		qc.clean()
+	}
+	qc.m[s] = *q
+	return
+}
+
+func (qc *QueryCache) lookup(s string) *Query {
+	qc.RLock()
+	defer qc.RUnlock()
+	if q, ok := qc.m[s]; ok {
+		return &q
+	}
+	return nil
+}
+
+func (qc *QueryCache) clean() {
+	i := rand.Intn(len(qc.m))
+	var k string
+	for k = range qc.m {
+		if i == 0 {
+			break
+		}
+		i--
+	}
+	delete(qc.m, k)
+}

filter_test.go

@@ -275,6 +275,14 @@ func BenchmarkNewQueryComplexOr(b *testing.B) {
 	}
 }
 
+func BenchmarkNewQueryCacheComplexOr(b *testing.B) {
+	c := NewQueryCache(1)
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		c.NewQuery(compOr)
+	}
+}
+
 func BenchmarkNewQuerySort(b *testing.B) {
 	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
@@ -303,6 +311,14 @@ func BenchmarkNewQuerySortComplexOr(b *testing.B) {
 	}
 }
 
+func BenchmarkNewQueryCacheSortComplexOr(b *testing.B) {
+	c := NewQueryCache(1)
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		c.NewQuery(compOrSort)
+	}
+}
+
 func BenchmarkFilterSimple(b *testing.B) {
 	b.ReportAllocs()
 	q, err := NewQuery(simple)