kgo: add LeaveGroupContext

This allows more control over timeouts when leaving a group or closing
the client, and also gives more insight into group leave errors.

Closes #556.

pkg/kgo/client.go

@@ -929,7 +929,10 @@ func (cl *Client) CloseAllowingRebalance() {
 	cl.Close()
 }
 
-// Close leaves any group and closes all connections and goroutines.
+// Close leaves any group and closes all connections and goroutines. This
+// function waits for the group to be left. If you want to force leave a group
+// immediately and ensure a speedy shutdown you can use LeaveGroupContext first
+// (and then Close will be immediate).
 //
 // If you are group consuming and have overridden the default
 // OnPartitionsRevoked, you must manually commit offsets before closing the
@@ -942,6 +945,10 @@ func (cl *Client) CloseAllowingRebalance() {
 // notification of revoked partitions. If you want to automatically allow
 // rebalancing, use CloseAllowingRebalance.
 func (cl *Client) Close() {
+	cl.close(cl.ctx)
+}
+
+func (cl *Client) close(ctx context.Context) (rerr error) {
 	defer cl.cfg.hooks.each(func(h Hook) {
 		if h, ok := h.(HookClientClosed); ok {
 			h.OnClientClosed(cl)
@@ -951,7 +958,7 @@ func (cl *Client) Close() {
 	c := &cl.consumer
 	c.kill.Store(true)
 	if c.g != nil {
-		cl.LeaveGroup()
+		rerr = cl.LeaveGroupContext(ctx)
 	} else if c.d != nil {
 		c.mu.Lock()                                           // lock for assign
 		c.assignPartitions(nil, assignInvalidateAll, nil, "") // we do not use a log message when not in a group
@@ -963,7 +970,7 @@ func (cl *Client) Close() {
 	// 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)
+	sessCloseCtx, sessCloseCancel := context.WithTimeout(ctx, time.Second)
 	var wg sync.WaitGroup
 	cl.allSinksAndSources(func(sns sinkAndSource) {
 		if sns.source.session.id != 0 {
@@ -1015,6 +1022,8 @@ func (cl *Client) Close() {
 			closing.Close()
 		}
 	}
+
+	return rerr
 }
 
 // Request issues a request to Kafka, waiting for and returning the response.

pkg/kgo/consumer_group.go

@@ -150,36 +150,82 @@ type groupConsumer struct {
 	// We set this once to manage the group lifecycle once.
 	managing bool
 
-	dying bool // set when closing, read in findNewAssignments
+	dying    bool // set when closing, read in findNewAssignments
+	left     chan struct{}
+	leaveErr error // set before left is closed
+}
+
+// LeaveGroup leaves a group. Close automatically leaves the group, so this is
+// only necessary to call if you plan to leave the group but continue to use
+// the client. If a rebalance is in progress, this function waits for the
+// rebalance to complete before the group can be left. This is necessary to
+// allow you to safely issue one final offset commit in OnPartitionsRevoked. If
+// you have overridden the default revoke, you must manually commit offsets
+// before leaving the group.
+//
+// If you have configured the group with an InstanceID, this does not leave the
+// group. With instance IDs, it is expected that clients will restart and
+// re-use the same instance ID. To leave a group using an instance ID, you must
+// manually issue a kmsg.LeaveGroupRequest or use an external tool (kafka
+// scripts or kcl).
+//
+// It is recommended to use LeaveGroupContext to see if the leave was
+// successful.
+func (cl *Client) LeaveGroup() {
+	cl.LeaveGroupContext(cl.ctx)
 }
 
-// LeaveGroup leaves a group if in one. Calling the client's Close function
-// also leaves a group, so this is only necessary to call if you plan to leave
-// the group and continue using the client. Note that if a rebalance is in
-// progress, this function waits for the rebalance to complete before the group
-// can be left. This is necessary to allow you to safely issue one final offset
-// commit in OnPartitionsRevoked. If you have overridden the default revoke,
-// you must manually commit offsets before leaving the group.
+// LeaveGroup leaves a group. Close automatically leaves the group, so this is
+// only necessary to call if you plan to leave the group but continue to use
+// the client. If a rebalance is in progress, this function waits for the
+// rebalance to complete before the group can be left. This is necessary to
+// allow you to safely issue one final offset commit in OnPartitionsRevoked. If
+// you have overridden the default revoke, you must manually commit offsets
+// before leaving the group.
+//
+// The context can be used to avoid waiting for the client to leave the group.
+// Not waiting may result in your client being stuck in the group and the
+// partitions this client was consuming being stuck until the session timeout.
+// This function returns any leave group error or context cancel error. If the
+// context is nil, this immediately leaves the group and does not wait and does
+// not return an error.
 //
 // If you have configured the group with an InstanceID, this does not leave the
 // group. With instance IDs, it is expected that clients will restart and
 // re-use the same instance ID. To leave a group using an instance ID, you must
 // manually issue a kmsg.LeaveGroupRequest or use an external tool (kafka
 // scripts or kcl).
-func (cl *Client) LeaveGroup() {
+func (cl *Client) LeaveGroupContext(ctx context.Context) error {
 	c := &cl.consumer
 	if c.g == nil {
-		return
+		return nil
+	}
+	var immediate bool
+	if ctx == nil {
+		var cancel func()
+		ctx, cancel = context.WithCancel(context.Background())
+		cancel()
+		immediate = true
 	}
 
-	c.waitAndAddRebalance()
-	c.mu.Lock() // lock for assign
-	c.assignPartitions(nil, assignInvalidateAll, nil, "invalidating all assignments in LeaveGroup")
-	wait := c.g.leave()
-	c.mu.Unlock()
-	c.unaddRebalance()
+	go func() {
+		c.waitAndAddRebalance()
+		c.mu.Lock() // lock for assign
+		c.assignPartitions(nil, assignInvalidateAll, nil, "invalidating all assignments in LeaveGroup")
+		c.g.leave(ctx)
+		c.mu.Unlock()
+		c.unaddRebalance()
+	}()
 
-	wait() // wait after we unlock
+	select {
+	case <-ctx.Done():
+		if immediate {
+			return nil
+		}
+		return ctx.Err()
+	case <-c.g.left:
+		return c.g.leaveErr
+	}
 }
 
 // GroupMetadata returns the current group member ID and generation, or an
@@ -214,6 +260,8 @@ func (c *consumer) initGroup() {
 		rejoinCh:         make(chan string, 1),
 		heartbeatForceCh: make(chan func(error)),
 		using:            make(map[string]int),
+
+		left: make(chan struct{}),
 	}
 	c.g = g
 	if !g.cfg.setCommitCallback {
@@ -411,7 +459,7 @@ func (g *groupConsumer) manage() {
 	}
 }
 
-func (g *groupConsumer) leave() (wait func()) {
+func (g *groupConsumer) leave(ctx context.Context) {
 	// If g.using is nonzero before this check, then a manage goroutine has
 	// started. If not, it will never start because we set dying.
 	g.mu.Lock()
@@ -421,43 +469,46 @@ func (g *groupConsumer) leave() (wait func()) {
 	g.cancel()
 	g.mu.Unlock()
 
-	done := make(chan struct{})
-
 	go func() {
-		defer close(done)
-
 		if wasManaging {
 			// We want to wait for the manage goroutine to be done
 			// so that we call the user's on{Assign,RevokeLost}.
 			<-g.manageDone
 		}
-
 		if wasDead {
 			// If we already called leave(), then we just wait for
 			// the prior leave to finish and we avoid re-issuing a
 			// LeaveGroup request.
 			return
 		}
 
-		if g.cfg.instanceID == nil {
-			g.cfg.logger.Log(LogLevelInfo, "leaving group",
-				"group", g.cfg.group,
-				"member_id", g.memberID, // lock not needed now since nothing can change it (manageDone)
-			)
-			// If we error when leaving, there is not much
-			// we can do. We may as well just return.
-			req := kmsg.NewPtrLeaveGroupRequest()
-			req.Group = g.cfg.group
-			req.MemberID = g.memberID
-			member := kmsg.NewLeaveGroupRequestMember()
-			member.MemberID = g.memberID
-			member.Reason = kmsg.StringPtr("client leaving group per normal operation")
-			req.Members = append(req.Members, member)
-			req.RequestWith(g.cl.ctx, g.cl)
+		defer close(g.left)
+
+		if g.cfg.instanceID != nil {
+			return
 		}
-	}()
 
-	return func() { <-done }
+		g.cfg.logger.Log(LogLevelInfo, "leaving group",
+			"group", g.cfg.group,
+			"member_id", g.memberID, // lock not needed now since nothing can change it (manageDone)
+		)
+		// If we error when leaving, there is not much
+		// we can do. We may as well just return.
+		req := kmsg.NewPtrLeaveGroupRequest()
+		req.Group = g.cfg.group
+		req.MemberID = g.memberID
+		member := kmsg.NewLeaveGroupRequestMember()
+		member.MemberID = g.memberID
+		member.Reason = kmsg.StringPtr("client leaving group per normal operation")
+		req.Members = append(req.Members, member)
+
+		resp, err := req.RequestWith(ctx, g.cl)
+		if err != nil {
+			g.leaveErr = err
+			return
+		}
+		g.leaveErr = kerr.ErrorForCode(resp.ErrorCode)
+	}()
 }
 
 // returns the difference of g.nowAssigned and g.lastAssigned.