vendor: google.golang.org/grpc v1.58.3

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go

@@ -0,0 +1,125 @@
+/*
+ *
+ * Copyright 2022 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"
+
+	"google.golang.org/grpc/internal/buffer"
+)
+
+// CallbackSerializer provides a mechanism to schedule callbacks in a
+// synchronized manner. It provides a FIFO guarantee on the order of execution
+// of scheduled callbacks. New callbacks can be scheduled by invoking the
+// Schedule() method.
+//
+// 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 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 {
+	cs := &CallbackSerializer{
+		done:      make(chan struct{}),
+		callbacks: buffer.NewUnbounded(),
+	}
+	go cs.run(ctx)
+	return cs
+}
+
+// Schedule adds a callback to be scheduled after existing callbacks are run.
+//
+// Callbacks are expected to honor the context when performing any blocking
+// operations, and should return early when the context is canceled.
+//
+// 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 (cs *CallbackSerializer) Schedule(f func(ctx context.Context)) bool {
+	cs.closedMu.Lock()
+	defer cs.closedMu.Unlock()
+
+	if cs.closed {
+		return false
+	}
+	cs.callbacks.Put(f)
+	return true
+}
+
+func (cs *CallbackSerializer) run(ctx context.Context) {
+	var backlog []func(context.Context)
+
+	defer close(cs.done)
+	for ctx.Err() == nil {
+		select {
+		case <-ctx.Done():
+			// Do nothing here. Next iteration of the for loop will not happen,
+			// since ctx.Err() would be non-nil.
+		case callback, ok := <-cs.callbacks.Get():
+			if !ok {
+				return
+			}
+			cs.callbacks.Load()
+			callback.(func(ctx context.Context))(ctx)
+		}
+	}
+
+	// Fetch pending callbacks if any, and execute them before returning from
+	// this method and closing cs.done.
+	cs.closedMu.Lock()
+	cs.closed = true
+	backlog = cs.fetchPendingCallbacks()
+	cs.callbacks.Close()
+	cs.closedMu.Unlock()
+	for _, b := range backlog {
+		b(ctx)
+	}
+}
+
+func (cs *CallbackSerializer) fetchPendingCallbacks() []func(context.Context) {
+	var backlog []func(context.Context)
+	for {
+		select {
+		case b := <-cs.callbacks.Get():
+			backlog = append(backlog, b.(func(context.Context)))
+			cs.callbacks.Load()
+		default:
+			return backlog
+		}
+	}
+}
+
+// Done returns a channel that is closed after the context passed to
+// NewCallbackSerializer is canceled and all callbacks have been executed.
+func (cs *CallbackSerializer) Done() <-chan struct{} {
+	return cs.done
+}