From bae7e7c3e696b5b09cff701d4055fb1ef08e06c7 Mon Sep 17 00:00:00 2001
From: "Sascha L. Teichmann" <sascha.teichmann@intevation.de>
Date: Tue, 10 May 2016 21:02:16 +0200
Subject: [PATCH] Made size of hashes LRU cache a parameter set by the
 webmapper.

---
 cmd/mtwebmapper/tilesupdater.go |  5 ++++-
 common/basetilehash.go          | 14 +++++++-------
 common/basetilehash_test.go     |  2 +-
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/cmd/mtwebmapper/tilesupdater.go b/cmd/mtwebmapper/tilesupdater.go
index a4f9d2f..9f5b14e 100644
--- a/cmd/mtwebmapper/tilesupdater.go
+++ b/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")
 
diff --git a/common/basetilehash.go b/common/basetilehash.go
index f27af76..89a8518 100644
--- a/common/basetilehash.go
+++ b/common/basetilehash.go
@@ -9,8 +9,6 @@ import (
 	"sync"
 )
 
-const btMaxEntries = 256
-
 type btKey struct {
 	x int
 	y int
@@ -24,14 +22,16 @@ type btHashEntry struct {
 }
 
 type BaseTileHash struct {
-	hashes map[btKey]*btHashEntry
-	root   btHashEntry
+	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)
diff --git a/common/basetilehash_test.go b/common/basetilehash_test.go
index a45f5cf..7aa89c6 100644
--- a/common/basetilehash_test.go
+++ b/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++ {