2 files changed, 195 insertions, 5 deletions
diff --git a/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go b/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go
index 79993d343..37b8d4117 100644
--- a/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go
+++ b/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go
@@ -20,6 +20,7 @@ package grpcsync
 
 import (
 	"context"
+	"sync"
 
 	"google.golang.org/grpc/internal/buffer"
 )
@@ -31,15 +32,26 @@ import (
 //
 // This type is safe for concurrent access.
 type CallbackSerializer struct {
+	// Done is closed once the serializer is shut down completely, i.e all
+	// scheduled callbacks are executed and the serializer has deallocated all
+	// its resources.
+	Done chan struct{}
+
 	callbacks *buffer.Unbounded
+	closedMu  sync.Mutex
+	closed    bool
 }
 
 // NewCallbackSerializer returns a new CallbackSerializer instance. The provided
 // context will be passed to the scheduled callbacks. Users should cancel the
 // provided context to shutdown the CallbackSerializer. It is guaranteed that no
-// callbacks will be executed once this context is canceled.
+// callbacks will be added once this context is canceled, and any pending un-run
+// callbacks will be executed before the serializer is shut down.
 func NewCallbackSerializer(ctx context.Context) *CallbackSerializer {
-	t := &CallbackSerializer{callbacks: buffer.NewUnbounded()}
+	t := &CallbackSerializer{
+		Done:      make(chan struct{}),
+		callbacks: buffer.NewUnbounded(),
+	}
 	go t.run(ctx)
 	return t
 }
@@ -48,18 +60,60 @@ func NewCallbackSerializer(ctx context.Context) *CallbackSerializer {
 //
 // Callbacks are expected to honor the context when performing any blocking
 // operations, and should return early when the context is canceled.
-func (t *CallbackSerializer) Schedule(f func(ctx context.Context)) {
+//
+// Return value indicates if the callback was successfully added to the list of
+// callbacks to be executed by the serializer. It is not possible to add
+// callbacks once the context passed to NewCallbackSerializer is cancelled.
+func (t *CallbackSerializer) Schedule(f func(ctx context.Context)) bool {
+	t.closedMu.Lock()
+	defer t.closedMu.Unlock()
+
+	if t.closed {
+		return false
+	}
 	t.callbacks.Put(f)
+	return true
 }
 
 func (t *CallbackSerializer) run(ctx context.Context) {
+	var backlog []func(context.Context)
+
+	defer close(t.Done)
 	for ctx.Err() == nil {
 		select {
 		case <-ctx.Done():
-			return
-		case callback := <-t.callbacks.Get():
+			// Do nothing here. Next iteration of the for loop will not happen,
+			// since ctx.Err() would be non-nil.
+		case callback, ok := <-t.callbacks.Get():
+			if !ok {
+				return
+			}
 			t.callbacks.Load()
 			callback.(func(ctx context.Context))(ctx)
 		}
 	}
+
+	// Fetch pending callbacks if any, and execute them before returning from
+	// this method and closing t.Done.
+	t.closedMu.Lock()
+	t.closed = true
+	backlog = t.fetchPendingCallbacks()
+	t.callbacks.Close()
+	t.closedMu.Unlock()
+	for _, b := range backlog {
+		b(ctx)
+	}
+}
+
+func (t *CallbackSerializer) fetchPendingCallbacks() []func(context.Context) {
+	var backlog []func(context.Context)
+	for {
+		select {
+		case b := <-t.callbacks.Get():
+			backlog = append(backlog, b.(func(context.Context)))
+			t.callbacks.Load()
+		default:
+			return backlog
+		}
+	}
 }
diff --git a/vendor/google.golang.org/grpc/internal/grpcsync/pubsub.go b/vendor/google.golang.org/grpc/internal/grpcsync/pubsub.go
new file mode 100644
index 000000000..f58b5ffa6
--- /dev/null
+++ b/vendor/google.golang.org/grpc/internal/grpcsync/pubsub.go
@@ -0,0 +1,136 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpcsync
+
+import (
+	"context"
+	"sync"
+)
+
+// Subscriber represents an entity that is subscribed to messages published on
+// a PubSub. It wraps the callback to be invoked by the PubSub when a new
+// message is published.
+type Subscriber interface {
+	// OnMessage is invoked when a new message is published. Implementations
+	// must not block in this method.
+	OnMessage(msg interface{})
+}
+
+// PubSub is a simple one-to-many publish-subscribe system that supports
+// messages of arbitrary type. It guarantees that messages are delivered in
+// the same order in which they were published.
+//
+// Publisher invokes the Publish() method to publish new messages, while
+// subscribers interested in receiving these messages register a callback
+// via the Subscribe() method.
+//
+// Once a PubSub is stopped, no more messages can be published, and
+// it is guaranteed that no more subscriber callback will be invoked.
+type PubSub struct {
+	cs     *CallbackSerializer
+	cancel context.CancelFunc
+
+	// Access to the below fields are guarded by this mutex.
+	mu          sync.Mutex
+	msg         interface{}
+	subscribers map[Subscriber]bool
+	stopped     bool
+}
+
+// NewPubSub returns a new PubSub instance.
+func NewPubSub() *PubSub {
+	ctx, cancel := context.WithCancel(context.Background())
+	return &PubSub{
+		cs:          NewCallbackSerializer(ctx),
+		cancel:      cancel,
+		subscribers: map[Subscriber]bool{},
+	}
+}
+
+// Subscribe registers the provided Subscriber to the PubSub.
+//
+// If the PubSub contains a previously published message, the Subscriber's
+// OnMessage() callback will be invoked asynchronously with the existing
+// message to begin with, and subsequently for every newly published message.
+//
+// The caller is responsible for invoking the returned cancel function to
+// unsubscribe itself from the PubSub.
+func (ps *PubSub) Subscribe(sub Subscriber) (cancel func()) {
+	ps.mu.Lock()
+	defer ps.mu.Unlock()
+
+	if ps.stopped {
+		return func() {}
+	}
+
+	ps.subscribers[sub] = true
+
+	if ps.msg != nil {
+		msg := ps.msg
+		ps.cs.Schedule(func(context.Context) {
+			ps.mu.Lock()
+			defer ps.mu.Unlock()
+			if !ps.subscribers[sub] {
+				return
+			}
+			sub.OnMessage(msg)
+		})
+	}
+
+	return func() {
+		ps.mu.Lock()
+		defer ps.mu.Unlock()
+		delete(ps.subscribers, sub)
+	}
+}
+
+// Publish publishes the provided message to the PubSub, and invokes
+// callbacks registered by subscribers asynchronously.
+func (ps *PubSub) Publish(msg interface{}) {
+	ps.mu.Lock()
+	defer ps.mu.Unlock()
+
+	if ps.stopped {
+		return
+	}
+
+	ps.msg = msg
+	for sub := range ps.subscribers {
+		s := sub
+		ps.cs.Schedule(func(context.Context) {
+			ps.mu.Lock()
+			defer ps.mu.Unlock()
+			if !ps.subscribers[s] {
+				return
+			}
+			s.OnMessage(msg)
+		})
+	}
+}
+
+// Stop shuts down the PubSub and releases any resources allocated by it.
+// It is guaranteed that no subscriber callbacks would be invoked once this
+// method returns.
+func (ps *PubSub) Stop() {
+	ps.mu.Lock()
+	defer ps.mu.Unlock()
+	ps.stopped = true
+
+	ps.cancel()
+}