From 65119c1ee4985cd695e9a6ece3825f18864255ef Mon Sep 17 00:00:00 2001
From: "Sascha L. Teichmann" <sascha.teichmann@intevation.de>
Date: Tue, 21 Mar 2017 16:25:58 +0100
Subject: [PATCH] Priotize again.

---
 cmd/mtredisalize/leveldb.go | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/cmd/mtredisalize/leveldb.go b/cmd/mtredisalize/leveldb.go
index 591afbd..1e5abd6 100644
--- a/cmd/mtredisalize/leveldb.go
+++ b/cmd/mtredisalize/leveldb.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"log"
+	"sync"
 
 	"bitbucket.org/s_l_teichmann/mtsatellite/common"
 
@@ -21,6 +22,9 @@ type LevelDBBackend struct {
 	decoder     common.KeyTranscoder
 
 	changeTracker *changeTracker
+
+	priorityCond *sync.Cond
+	priority     int
 }
 
 type LevelDBSession struct {
@@ -71,6 +75,7 @@ func NewLeveDBBackend(
 		encoder:       encoder,
 		decoder:       decoder,
 		changeTracker: changeTracker,
+		priorityCond:  sync.NewCond(new(sync.Mutex)),
 	}
 
 	if !interleaved {
@@ -83,6 +88,28 @@ func NewLeveDBBackend(
 	return
 }
 
+func (ldb *LevelDBBackend) suspend() {
+	ldb.priorityCond.L.Lock()
+	for ldb.priority > 0 {
+		ldb.priorityCond.Wait()
+	}
+	ldb.priorityCond.L.Unlock()
+}
+
+func (ldb *LevelDBBackend) grab() {
+	ldb.priorityCond.L.Lock()
+	ldb.priority++
+	ldb.priorityCond.L.Unlock()
+}
+
+func (ldb *LevelDBBackend) ungrab() {
+	ldb.priorityCond.L.Lock()
+	if ldb.priority--; ldb.priority <= 0 {
+		ldb.priorityCond.Broadcast()
+	}
+	ldb.priorityCond.L.Unlock()
+}
+
 func (ldb *LevelDBBackend) buildCoverage() error {
 	log.Println("INFO: Start building coverage index (this may take some time)...")
 
@@ -153,6 +180,8 @@ func (ldbs *LevelDBSession) Fetch(hash, key []byte) (value []byte, err error) {
 	if key, err = ldbs.backend.decoder(key); err != nil {
 		return
 	}
+	ldbs.backend.grab()
+	defer ldbs.backend.ungrab()
 	ro := leveldb.NewReadOptions()
 	value, err = ldbs.backend.db.Get(ro, key)
 	//if err != nil {
@@ -184,6 +213,8 @@ func (ldbs *LevelDBSession) Store(hash, key, value []byte) (exists bool, err err
 	if key, err = ldbs.backend.decoder(key); err != nil {
 		return
 	}
+	ldbs.backend.grab()
+	defer ldbs.backend.ungrab()
 	if exists, err = keyExists(ldbs.backend.db, key); err != nil {
 		return
 	}
@@ -325,6 +356,7 @@ func (ldbs *LevelDBSession) plainSpatialQuery(
 		for _, r := range ldbs.backend.coverage.Query(c1, c2) {
 			a.Z, b.Z = int16(r.Z), int16(r.Z)
 			a.X, b.X = int16(r.X1), int16(r.X2)
+			ldbs.backend.suspend()
 			for a.Y = r.Y2; a.Y >= r.Y1; a.Y-- {
 				b.Y = a.Y
 				// The keys in the database are stored and ordered as strings
@@ -415,6 +447,7 @@ func (ldbs *LevelDBSession) interleavedSpatialQuery(
 				it.Next()
 			} else {
 				next := common.BigMin(zmin, zmax, zcode)
+				ldbs.backend.suspend()
 				//log.Printf("seeking to: %d\n", next)
 				it.Seek(common.ToBigEndian(next))
 				//log.Printf("seeking done: %d\n", next)