implement SharedShardCache

Author: robaho

maps.go

@@ -2,6 +2,7 @@ package go_concurrency
 
 import (
 	"sync"
+	"sync/atomic"
 )
 
 func nextPowerOf2(v int) int {
@@ -104,6 +105,41 @@ func (m *ShardCache) Put(key int, value int) {
 	m.maps[key%10][key] = value
 }
 
+const SharedShardMask = 16 - 1
+
+type SharedShardCache struct {
+	maps  [16]atomic.Value
+	locks [16]sync.Mutex
+}
+
+func NewSharedShardCache() *SharedShardCache {
+	m := SharedShardCache{}
+	for i := 0; i < 16; i++ {
+		m.maps[i].Store(make(map[int]int))
+	}
+	return &m
+}
+
+func (m *SharedShardCache) Get(key int) int {
+	m0 := m.maps[key&SharedShardMask]
+	return m0.Load().(map[int]int)[key]
+}
+
+func (m *SharedShardCache) Put(key int, value int) {
+	lock := m.locks[key&SharedShardMask]
+	lock.Lock()
+	m0 := m.maps[key&SharedShardMask].Load().(map[int]int)
+	// make a new map and atomically store, this could be optimized because if
+	// the key already exists in the map, we can safely update the value in the
+	// main map and just restore to enforce the memory fence
+	m1 := make(map[int]int)
+	for k, v := range m0 {
+		m1[k] = v
+	}
+	m1[key] = value
+	m.maps[key&SharedShardMask].Store(m1)
+}
+
 type UnsharedCache map[int]int
 
 func NewUnsharedCache() *UnsharedCache {

maps_test.go

@@ -9,14 +9,15 @@ import (
 	"time"
 )
 
-const NGOS = 2 // number of concurrent go routines for read/load tests
+const NGOS = 8 // number of concurrent go routines for read/load tests
 const Mask = (1024 * 1024) - 1
 
 var um = go_concurrency.NewUnsharedCache()
 var lm = go_concurrency.NewLockCache()
 var sm = go_concurrency.NewSyncCache()
 var cm = go_concurrency.NewChannelCache()
 var sc = go_concurrency.NewShardCache()
+var ssc = go_concurrency.NewSharedShardCache()
 var im = go_concurrency.NewIntMap(256000)   // so there are 4x collisions
 var im2 = go_concurrency.NewIntMap(1000000) // so there are no collisions
 
@@ -80,8 +81,8 @@ func BenchmarkMain(m *testing.B) {
 	m.ResetTimer()
 
 	impls := []go_concurrency.Cache{um, lm, sm, cm, sc, im, im2}
-	names := []string{"unshared", "lock", "sync", "channel", "shard", "intmap", "intmap2"}
-	multi := []bool{false, true, true, true, false, true, true}
+	names := []string{"unshared", "lock", "sync", "channel", "shard", "shareshard", "intmap", "intmap2"}
+	multi := []bool{false, true, true, true, false, true, true, true}
 
 	for i := 0; i < len(impls); i++ {
 		impl := impls[i]