Implemented a simple LRU cache with max 256 entries for base tile hasing. TODO: Improve test.

cmd/mtwebmapper/web/index.html

@@ -48,7 +48,7 @@
     <script type="text/javascript" src="js/leaflet.awesome-markers.js"></script>
     <script>
 
-var useWebsocket = false; // Set to true if you want websocket support
+var useWebsocket = true; // Set to true if you want websocket support
 
 L.Projection.NoWrap = {
     project: function (latlng) {

common/basetilehash.go

@@ -9,27 +9,81 @@ import (
 	"sync"
 )
 
+const btMaxEntries = 256
+
+type btKey struct {
+	x int
+	y int
+}
+
+type btHashEntry struct {
+	prev *btHashEntry
+	next *btHashEntry
+	hash []byte
+	btKey
+}
+
 type BaseTileHash struct {
-	// XXX: Maybe use some kind of LRU cache instead?
-	hashes map[struct{ x, y int }][]byte
+	hashes map[btKey]*btHashEntry
+	root   btHashEntry
 	sync.Mutex
 }
 
 func NewBaseTileHash() *BaseTileHash {
-	return &BaseTileHash{hashes: map[struct{ x, y int }][]byte{}}
+	bth := &BaseTileHash{
+		hashes: map[btKey]*btHashEntry{}}
+	bth.root.next = &bth.root
+	bth.root.prev = &bth.root
+	return bth
+}
+
+func (bth *BaseTileHash) toFront(entry *btHashEntry) {
+	if bth.root.next == entry {
+		return
+	}
+	entry.prev.next = entry.next
+	entry.next.prev = entry.prev
+	entry.next = bth.root.next
+	entry.prev = &bth.root
+	bth.root.next = entry
+}
+
+func (bth *BaseTileHash) removeLast() *btHashEntry {
+	last := bth.root.prev
+	bth.root.prev = last.prev
+	last.prev.next = &bth.root
+	delete(bth.hashes, last.btKey)
+	return last
+}
+
+func (bth *BaseTileHash) insertFront(entry *btHashEntry) {
+	entry.next = bth.root.next
+	entry.prev = &bth.root
+	bth.root.next.prev = entry
+	bth.root.next = entry
 }
 
 func (bth *BaseTileHash) Update(x, y int, hash []byte) bool {
-	key := struct{ x, y int }{x, y}
 	bth.Lock()
 	defer bth.Unlock()
+	key := btKey{x, y}
 	if old, found := bth.hashes[key]; found {
-		if !bytes.Equal(old, hash) {
-			bth.hashes[key] = hash
+		if !bytes.Equal(old.hash, hash) {
+			old.hash = hash
+			bth.toFront(old)
 			return true
 		}
 		return false
 	}
-	bth.hashes[key] = hash
+	var entry *btHashEntry
+	if len(bth.hashes) >= btMaxEntries {
+		entry = bth.removeLast()
+	} else {
+		entry = new(btHashEntry)
+	}
+	entry.btKey = key
+	entry.hash = hash
+	bth.hashes[key] = entry
+	bth.insertFront(entry)
 	return true
 }

common/basetilehash_test.go

@@ -0,0 +1,27 @@
+// Copyright 2016 by Sascha L. Teichmann
+// Use of this source code is governed by the MIT license
+// that can be found in the LICENSE file.
+
+package common
+
+import "testing"
+
+func TestBaseTileHash(t *testing.T) {
+	bth := NewBaseTileHash()
+	h1 := []byte{1}
+	h2 := []byte{2}
+	for i := 0; i < 600; i++ {
+		x := i % 200
+		for j := 0; j < 600; j++ {
+			y := j % 200
+			var h []byte
+			if j%2 == 0 {
+				h = h1
+			} else {
+				h = h2
+			}
+			_ = bth.Update(x, y, h)
+		}
+	}
+	t.Logf("size: %d\n", len(bth.hashes))
+}