diff --git a/client.go b/client.go
index 83828bb070..e9f3e909ff 100644
--- a/client.go
+++ b/client.go
@@ -440,19 +440,35 @@ func (cl *Client) eachDhtServer(f func(DhtServer)) {
 func (cl *Client) Close() (errs []error) {
 	var closeGroup sync.WaitGroup // For concurrent cleanup to complete before returning
 	cl.lock()
+
+	if cl.closed.IsSet() {
+		cl.unlock()
+		return
+	}
+
+	var mu sync.Mutex
 	for _, t := range cl.torrentsAsSlice() {
-		err := t.close(&closeGroup)
-		if err != nil {
-			errs = append(errs, err)
-		}
+		closeGroup.Add(1)
+
+		go func(t *Torrent) {
+			defer closeGroup.Done()
+
+			err := t.close()
+			if err != nil {
+				mu.Lock()
+				errs = append(errs, err)
+				mu.Unlock()
+			}
+		}(t)
 	}
+	cl.closed.Set()
+	cl.unlock()
+	closeGroup.Wait()
+	// don't close resources until torrent closes are complete
 	for i := range cl.onClose {
 		cl.onClose[len(cl.onClose)-1-i]()
 	}
-	cl.closed.Set()
-	cl.unlock()
 	cl.event.Broadcast()
-	closeGroup.Wait() // defer is LIFO. We want to Wait() after cl.unlock()
 	return
 }
 
@@ -1522,7 +1538,9 @@ func (cl *Client) dropTorrent(infoHash metainfo.Hash, wg *sync.WaitGroup) (err e
 		err = fmt.Errorf("no such torrent")
 		return
 	}
-	err = t.close(wg)
+	wg.Add(1)
+	defer wg.Done()
+	err = t.close()
 	delete(cl.torrents, infoHash)
 	return
 }
diff --git a/mmap_span/mmap_span.go b/mmap_span/mmap_span.go
index a8fb518dfa..e5b28418fc 100644
--- a/mmap_span/mmap_span.go
+++ b/mmap_span/mmap_span.go
@@ -39,11 +39,18 @@ func (ms *MMapSpan) Append(mMap Mmap) {
 func (ms *MMapSpan) Flush(onFlush func(size int64)) (errs []error) {
 	ms.mu.Lock()
 	defer ms.mu.Unlock()
-	if ms.flushTimer == nil {
+	if len(ms.mMaps) > 0 && ms.flushTimer == nil {
 		ms.flushTimer = time.AfterFunc(ms.FlushTime,
 			func() {
-				// TODO deal with logging errors
-				ms.flushMaps(onFlush, true)
+				ms.mu.Lock()
+				flushTimer := ms.flushTimer
+				ms.flushTimer = nil
+				ms.mu.Unlock()
+
+				if flushTimer != nil {
+					// TODO deal with logging errors
+					ms.flushMaps(onFlush, true)
+				}
 			})
 	}
 	return
@@ -63,21 +70,18 @@ func (ms *MMapSpan) flushMaps(onFlush func(size int64), lock bool) (errs []error
 		dirtyPieces = ms.dirtyPieces.Clone()
 		dirtySize = ms.dirtySize
 
-		if ms.flushTimer != nil {
-			ms.flushTimer = nil
-			for _, mMap := range ms.mMaps {
-				err := mMap.Flush()
-				if err != nil {
-					errs = append(errs, err)
+		for _, mMap := range ms.mMaps {
+			err := mMap.Flush()
+			if err != nil {
+				errs = append(errs, err)
 
-				}
 			}
+		}
 
-			if len(errs) == 0 {
-				flushedCallback = ms.FlushedCallback
-				ms.dirtyPieces = roaring.Bitmap{}
-				ms.dirtySize = 0
-			}
+		if len(errs) == 0 {
+			flushedCallback = ms.FlushedCallback
+			ms.dirtyPieces = roaring.Bitmap{}
+			ms.dirtySize = 0
 		}
 
 		return
diff --git a/torrent-piece-request-order.go b/torrent-piece-request-order.go
index 8d5aea011d..79ed2cbce4 100644
--- a/torrent-piece-request-order.go
+++ b/torrent-piece-request-order.go
@@ -33,10 +33,16 @@ func (t *Torrent) clientPieceRequestOrderKey() interface{} {
 	return t.storage.Capacity
 }
 
-func (t *Torrent) deletePieceRequestOrder() {
+func (t *Torrent) deletePieceRequestOrder(lockClient bool) {
 	if t.storage == nil {
 		return
 	}
+
+	if lockClient {
+		t.cl.lock()
+		defer t.cl.unlock()
+	}
+
 	cpro := t.cl.pieceRequestOrder
 	key := t.clientPieceRequestOrderKey()
 	pro := cpro[key]
diff --git a/torrent.go b/torrent.go
index 995219f194..5516ae28ea 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1065,52 +1065,53 @@ func (t *Torrent) numPiecesCompleted(lock bool) (num pieceIndex) {
 	return pieceIndex(t._completedPieces.GetCardinality())
 }
 
-func (t *Torrent) close(wg *sync.WaitGroup) (err error) {
+func (t *Torrent) close() (err error) {
 	if !t.closed.Set() {
 		err = errors.New("already closed")
 		return
 	}
+
 	for _, f := range t.onClose {
 		f()
 	}
 
+	func() {
+		t.mu.Lock()
+		defer t.mu.Unlock()
+
+		t.iterPeers(func(p *Peer) {
+			p.close(false)
+		}, false)
+	}()
+
 	if t.storage != nil {
-		closed := make(chan struct{})
-		defer func() { closed <- struct{}{} }()
-
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			<-closed
-			t.storageLock.Lock()
-			defer t.storageLock.Unlock()
-			if f := t.storage.Close; f != nil {
-				err1 := f()
-				if err1 != nil {
-					t.logger.WithDefaultLevel(log.Warning).Printf("error closing storage: %v", err1)
-				}
-			}
-		}()
+		t.deletePieceRequestOrder(true)
 	}
 
-	t.mu.Lock()
-	defer t.mu.Unlock()
+	func() {
+		t.mu.Lock()
+		defer t.mu.Unlock()
+		t.assertAllPiecesRelativeAvailabilityZero(false)
+		t.pex.Reset()
+		t.cl.event.Broadcast()
+		t.pieceStateChanges.Close()
+		t.updateWantPeersEvent(false)
+		if t.hashResults != nil {
+			close(t.hashResults)
+			t.hashResults = nil
+		}
+	}()
 
-	t.iterPeers(func(p *Peer) {
-		p.close(false)
-	}, false)
 	if t.storage != nil {
-		t.deletePieceRequestOrder()
-	}
-	t.assertAllPiecesRelativeAvailabilityZero(false)
-	t.pex.Reset()
-	t.cl.event.Broadcast()
-	t.pieceStateChanges.Close()
-	t.updateWantPeersEvent(false)
-	if t.hashResults != nil {
-		close(t.hashResults)
-		t.hashResults = nil
+		t.storageLock.Lock()
+		defer t.storageLock.Unlock()
+		if f := t.storage.Close; f != nil {
+			if err := f(); err != nil {
+				t.logger.WithDefaultLevel(log.Warning).Printf("error closing storage: %v", err)
+			}
+		}
 	}
+
 	return
 }
 
@@ -2643,7 +2644,7 @@ func (t *Torrent) pieceHashed(piece pieceIndex, passed bool, hashIoErr error) {
 		}
 
 		err := p.Storage().MarkComplete(!hasDirtyChunks)
-		
+
 		if err == nil {
 			t.allStats(func(cs *ConnStats) {
 				cs.pieceCompleted(int64(p.length(true)))
@@ -2773,7 +2774,7 @@ func (t *Torrent) tryCreateMorePieceHashers(lock bool) {
 			}
 			if t.hashResults == nil {
 				t.hashResults = make(chan hashResult, t.cl.config.PieceHashersPerTorrent*16)
-				go t.processHashResults()
+				go t.processHashResults(t.hashResults)
 			}
 		}()
 	}
@@ -2856,7 +2857,14 @@ func (t *Torrent) tryCreatePieceHasher(lock bool) bool {
 				cs.pieceHashed(length)
 			})
 
-			t.hashResults <- hashResult{p.index, correct, failedPeers, copyErr}
+			t.mu.RLock()
+			hashResults := t.hashResults
+			t.mu.RUnlock()
+
+			select {
+			case hashResults <- hashResult{p.index, correct, failedPeers, copyErr}:
+			case <-t.closed.Done():
+			}
 		}
 	}()
 
@@ -2870,7 +2878,7 @@ type hashResult struct {
 	copyErr     error
 }
 
-func (t *Torrent) processHashResults() {
+func (t *Torrent) processHashResults(hashResults chan hashResult) {
 
 	g, ctx := errgroup.WithContext(context.Background())
 	_, cancel := context.WithCancel(ctx)
@@ -2883,12 +2891,25 @@ func (t *Torrent) processHashResults() {
 	defer cancel()
 
 	for !t.closed.IsSet() {
-		results := []hashResult{<-t.hashResults}
+		results := []hashResult{}
+
+		select {
+		case result, ok := <-hashResults:
+			if ok {
+				results = append(results, result)
+			}
+		case <-t.closed.Done():
+			return
+		}
 
 		for done := false; !done; {
 			select {
-			case result := <-t.hashResults:
-				results = append(results, result)
+			case result, ok := <-hashResults:
+				if ok {
+					results = append(results, result)
+				}
+			case <-t.closed.Done():
+				return
 			default:
 				done = true
 			}
diff --git a/torrent_test.go b/torrent_test.go
index 561f793d46..6c04951697 100644
--- a/torrent_test.go
+++ b/torrent_test.go
@@ -6,7 +6,6 @@ import (
 	"net"
 	"os"
 	"path/filepath"
-	"sync"
 	"testing"
 
 	g "github.com/anacrolix/generics"
@@ -247,7 +246,6 @@ func TestRelativeAvailabilityHaveNone(t *testing.T) {
 	tt.onSetInfo(true, true)
 	err = pc.peerSentHaveNone(true)
 	c.Assert(err, qt.IsNil)
-	var wg sync.WaitGroup
-	tt.close(&wg)
+	tt.close()
 	tt.assertAllPiecesRelativeAvailabilityZero(true)
 }
diff --git a/tracker_scraper.go b/tracker_scraper.go
index f3f4f54d24..4d32a7cbac 100644
--- a/tracker_scraper.go
+++ b/tracker_scraper.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"math/rand"
 	"net"
 	"net/url"
 	"sync"
@@ -72,18 +73,52 @@ type trackerAnnounceResult struct {
 	Completed time.Time
 }
 
+type ilu struct {
+	err        error
+	ips        []net.IP
+	lookupTime time.Time
+}
+
+var ipc = map[string]*ilu{}
+var ipcmu sync.RWMutex
+
 func (me *trackerScraper) getIp() (ip net.IP, err error) {
-	var ips []net.IP
-	if me.lookupTrackerIp != nil {
-		ips, err = me.lookupTrackerIp(&me.u)
-	} else {
-		// Do a regular dns lookup
-		ips, err = net.LookupIP(me.u.Hostname())
+	// cache the ip lookup for 15 mins, this avoids
+	// spamming DNS on os's that don't cache DNS lookups
+	//  Cache TTL between 1 and 6 hours
+
+	ipcmu.RLock()
+	lu := ipc[me.u.String()]
+	ipcmu.RUnlock()
+
+	if lu == nil ||
+		time.Since(lu.lookupTime) > time.Hour+time.Duration(rand.Int63n(int64(5*time.Hour))) ||
+		lu.err != nil && time.Since(lu.lookupTime) > 15*time.Minute {
+		var ips []net.IP
+
+		if me.lookupTrackerIp != nil {
+			ips, err = me.lookupTrackerIp(&me.u)
+		} else {
+			// Do a regular dns lookup
+			ips, err = net.LookupIP(me.u.Hostname())
+		}
+
+		ipcmu.Lock()
+		lu = &ilu{
+			err:        err,
+			ips:        ips,
+			lookupTime: time.Now(),
+		}
+		ipc[me.u.String()] = lu
+		ipcmu.Unlock()
+
 	}
-	if err != nil {
+
+	if lu.err != nil {
 		return
 	}
-	if len(ips) == 0 {
+
+	if len(lu.ips) == 0 {
 		err = errors.New("no ips")
 		return
 	}
@@ -93,7 +128,7 @@ func (me *trackerScraper) getIp() (ip net.IP, err error) {
 		err = errors.New("client is closed")
 		return
 	}
-	for _, ip = range ips {
+	for _, ip = range lu.ips {
 		if me.t.cl.ipIsBlocked(ip) {
 			continue
 		}
@@ -109,6 +144,7 @@ func (me *trackerScraper) getIp() (ip net.IP, err error) {
 		}
 		return
 	}
+
 	err = errors.New("no acceptable ips")
 	return
 }