Made size of hashes LRU cache a parameter set by the webmapper.

cmd/mtwebmapper/tilesupdater.go

@@ -24,6 +24,9 @@ import (
 	"bitbucket.org/s_l_teichmann/mtsatellite/common"
 )
 
+// Number of check sums to keep in memory.
+const maxHashedTiles = 256
+
 type baseTilesUpdates interface {
 	BaseTilesUpdated([]xz)
 }
@@ -177,7 +180,7 @@ func activeChanges(changes []xzc) []xz {
 
 func (tu *tileUpdater) doUpdates() {
 
-	bth := common.NewBaseTileHash()
+	bth := common.NewBaseTileHash(maxHashedTiles)
 
 	baseDir := filepath.Join(tu.mapDir, "8")
 

common/basetilehash.go

@@ -9,8 +9,6 @@ import (
 	"sync"
 )
 
-const btMaxEntries = 256
-
 type btKey struct {
 	x int
 	y int
@@ -25,13 +23,15 @@ type btHashEntry struct {
 
 type BaseTileHash struct {
 	hashes     map[btKey]*btHashEntry
+	maxEntries int
 	root       btHashEntry
 	sync.Mutex
 }
 
-func NewBaseTileHash() *BaseTileHash {
+func NewBaseTileHash(maxEntries int) *BaseTileHash {
 	bth := &BaseTileHash{
-		hashes: map[btKey]*btHashEntry{}}
+		hashes:     map[btKey]*btHashEntry{},
+		maxEntries: maxEntries}
 	bth.root.next = &bth.root
 	bth.root.prev = &bth.root
 	return bth
@@ -76,7 +76,7 @@ func (bth *BaseTileHash) Update(x, y int, hash []byte) bool {
 		return false
 	}
 	var entry *btHashEntry
-	if len(bth.hashes) >= btMaxEntries {
+	if len(bth.hashes) >= bth.maxEntries {
 		entry = bth.removeLast()
 	} else {
 		entry = new(btHashEntry)

common/basetilehash_test.go

@@ -7,7 +7,7 @@ package common
 import "testing"
 
 func TestBaseTileHash(t *testing.T) {
-	bth := NewBaseTileHash()
+	bth := NewBaseTileHash(256)
 	h1 := []byte{1}
 	h2 := []byte{2}
 	for i := 0; i < 600; i++ {