kgo: fix race between client closing and purging

Purging topics can actually restart consuming.
This can race with killing fetch sessions while closing.
Purging internally calls assignPartitions with the consumer topics.
In general, we need to prevent anything resuming consuming no matter
what, so we add a bool field to the client that forcibly prevents
consuming.

pkg/kgo/client.go

@@ -947,18 +947,19 @@ func (cl *Client) Close() {
 	})
 
 	c := &cl.consumer
+	c.kill.Store(true)
 	if c.g != nil {
 		cl.LeaveGroup()
 	} else if c.d != nil {
-		c.mu.Lock()                                                          // lock for assign
-		c.assignPartitions(nil, assignInvalidateAll, noTopicsPartitions, "") // we do not use a log message when not in a group
+		c.mu.Lock()                                           // lock for assign
+		c.assignPartitions(nil, assignInvalidateAll, nil, "") // we do not use a log message when not in a group
 		c.mu.Unlock()
 	}
 
 	// After the above, consumers cannot consume anymore. LeaveGroup
-	// internally assigns noTopicsPartitions, which uses noConsumerSession,
-	// which prevents loopFetch from starting. Assigning also waits for the
-	// prior session to be complete, meaning loopFetch cannot be running.
+	// internally assigns nil, which uses noConsumerSession, which prevents
+	// loopFetch from starting. Assigning also waits for the prior session
+	// to be complete, meaning loopFetch cannot be running.
 
 	sessCloseCtx, sessCloseCancel := context.WithTimeout(cl.ctx, time.Second)
 	var wg sync.WaitGroup

pkg/kgo/consumer.go

@@ -196,6 +196,7 @@ type consumer struct {
 	sessionChangeMu sync.Mutex
 
 	session atomic.Value // *consumerSession
+	kill    atomic.Bool
 
 	usingCursors usedCursors
 
@@ -927,8 +928,13 @@ func (f fmtAssignment) String() string {
 	return sb.String()
 }
 
-// assignPartitions, called under the consumer's mu, is used to set new
-// cursors or add to the existing cursors.
+// assignPartitions, called under the consumer's mu, is used to set new cursors
+// or add to the existing cursors.
+//
+// We do not need to pass tps when we are bumping the session or when we are
+// invalidating all. All other cases, we want the tps -- the logic below does
+// not fully differentiate needing to start a new session vs. just reusing the
+// old (third if case below)
 func (c *consumer) assignPartitions(assignments map[string]map[int32]Offset, how assignHow, tps *topicsPartitions, why string) {
 	if c.mu.TryLock() {
 		c.mu.Unlock()
@@ -1058,7 +1064,7 @@ func (c *consumer) assignPartitions(assignments map[string]map[int32]Offset, how
 
 	// This assignment could contain nothing (for the purposes of
 	// invalidating active fetches), so we only do this if needed.
-	if len(assignments) == 0 || how == assignInvalidateMatching || how == assignPurgeMatching || how == assignSetMatching || how == assignBumpSession {
+	if len(assignments) == 0 || how != assignWithoutInvalidating {
 		return
 	}
 
@@ -1565,7 +1571,7 @@ func (c *consumer) stopSession() (listOrEpochLoads, *topicsPartitions) {
 	session := c.loadSession()
 
 	if session == noConsumerSession {
-		return listOrEpochLoads{}, noTopicsPartitions // we had no session
+		return listOrEpochLoads{}, nil // we had no session
 	}
 
 	// Before storing noConsumerSession, cancel our old. This pairs
@@ -1621,6 +1627,9 @@ func (c *consumer) stopSession() (listOrEpochLoads, *topicsPartitions) {
 // 1 worker allows for initialization work to prevent the session from being
 // immediately stopped.
 func (c *consumer) startNewSession(tps *topicsPartitions) *consumerSession {
+	if c.kill.Load() {
+		tps = nil
+	}
 	session := c.newConsumerSession(tps)
 	c.session.Store(session)
 

pkg/kgo/consumer_group.go

@@ -174,7 +174,7 @@ func (cl *Client) LeaveGroup() {
 
 	c.waitAndAddRebalance()
 	c.mu.Lock() // lock for assign
-	c.assignPartitions(nil, assignInvalidateAll, noTopicsPartitions, "invalidating all assignments in LeaveGroup")
+	c.assignPartitions(nil, assignInvalidateAll, nil, "invalidating all assignments in LeaveGroup")
 	wait := c.g.leave()
 	c.mu.Unlock()
 	c.unaddRebalance()

pkg/kgo/topics_and_partitions.go

@@ -250,8 +250,6 @@ type topicPartitions struct {
 
 func (t *topicPartitions) load() *topicPartitionsData { return t.v.Load().(*topicPartitionsData) }
 
-var noTopicsPartitions = newTopicsPartitions()
-
 func newTopicsPartitions() *topicsPartitions {
 	var t topicsPartitions
 	t.v.Store(make(topicsPartitionsData))