[tor-commits] [snowflake/main] Fix data race for Peers.collection

[cohosh at torproject.org]

commit e3351cb08abe6b806fa018bc8915f0f5ae045a40
Author: Cecylia Bocovich <cohosh at torproject.org>
Date:   Mon Jun 21 15:39:41 2021 -0400

    Fix data race for Peers.collection
    
    We used a WaitGroup to prevent a call to Peers.End from melting
    snowflakes while a new one is being collected. However, calls to
    WaitGroup.Add are in a race with WaitGroup.Wait. To fix this, we use a
    Mutex instead.
---
 client/lib/peers.go | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/client/lib/peers.go b/client/lib/peers.go
index 66373f1..7fba572 100644
--- a/client/lib/peers.go
+++ b/client/lib/peers.go
@@ -28,7 +28,7 @@ type Peers struct {
 
 	melt chan struct{}
 
-	collection sync.WaitGroup
+	collectLock sync.Mutex
 }
 
 // Construct a fresh container of remote peers.
@@ -48,8 +48,8 @@ func NewPeers(tongue Tongue) (*Peers, error) {
 // As part of |SnowflakeCollector| interface.
 func (p *Peers) Collect() (*WebRTCPeer, error) {
 	// Engage the Snowflake Catching interface, which must be available.
-	p.collection.Add(1)
-	defer p.collection.Done()
+	p.collectLock.Lock()
+	defer p.collectLock.Unlock()
 	select {
 	case <-p.melt:
 		return nil, fmt.Errorf("Snowflakes have melted")
@@ -121,7 +121,8 @@ func (p *Peers) purgeClosedPeers() {
 // Close all Peers contained here.
 func (p *Peers) End() {
 	close(p.melt)
-	p.collection.Wait()
+	p.collectLock.Lock()
+	defer p.collectLock.Unlock()
 	close(p.snowflakeChan)
 	cnt := p.Count()
 	for e := p.activePeers.Front(); e != nil; {