125 lines
3.6 KiB
Go
125 lines
3.6 KiB
Go
/*
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*
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* Copyright 2022 gRPC authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*/
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package grpcsync
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import (
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"context"
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"sync"
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"google.golang.org/grpc/internal/buffer"
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)
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// CallbackSerializer provides a mechanism to schedule callbacks in a
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// synchronized manner. It provides a FIFO guarantee on the order of execution
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// of scheduled callbacks. New callbacks can be scheduled by invoking the
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// Schedule() method.
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//
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// This type is safe for concurrent access.
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type CallbackSerializer struct {
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// done is closed once the serializer is shut down completely, i.e all
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// scheduled callbacks are executed and the serializer has deallocated all
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// its resources.
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done chan struct{}
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callbacks *buffer.Unbounded
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closedMu sync.Mutex
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closed bool
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}
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// NewCallbackSerializer returns a new CallbackSerializer instance. The provided
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// context will be passed to the scheduled callbacks. Users should cancel the
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// provided context to shutdown the CallbackSerializer. It is guaranteed that no
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// callbacks will be added once this context is canceled, and any pending un-run
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// callbacks will be executed before the serializer is shut down.
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func NewCallbackSerializer(ctx context.Context) *CallbackSerializer {
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cs := &CallbackSerializer{
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done: make(chan struct{}),
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callbacks: buffer.NewUnbounded(),
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}
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go cs.run(ctx)
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return cs
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}
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// Schedule adds a callback to be scheduled after existing callbacks are run.
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//
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// Callbacks are expected to honor the context when performing any blocking
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// operations, and should return early when the context is canceled.
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//
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// Return value indicates if the callback was successfully added to the list of
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// callbacks to be executed by the serializer. It is not possible to add
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// callbacks once the context passed to NewCallbackSerializer is cancelled.
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func (cs *CallbackSerializer) Schedule(f func(ctx context.Context)) bool {
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cs.closedMu.Lock()
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defer cs.closedMu.Unlock()
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if cs.closed {
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return false
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}
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cs.callbacks.Put(f)
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return true
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}
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func (cs *CallbackSerializer) run(ctx context.Context) {
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var backlog []func(context.Context)
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defer close(cs.done)
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for ctx.Err() == nil {
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select {
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case <-ctx.Done():
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// Do nothing here. Next iteration of the for loop will not happen,
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// since ctx.Err() would be non-nil.
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case callback, ok := <-cs.callbacks.Get():
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if !ok {
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return
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}
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cs.callbacks.Load()
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callback.(func(ctx context.Context))(ctx)
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}
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}
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// Fetch pending callbacks if any, and execute them before returning from
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// this method and closing cs.done.
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cs.closedMu.Lock()
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cs.closed = true
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backlog = cs.fetchPendingCallbacks()
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cs.callbacks.Close()
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cs.closedMu.Unlock()
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for _, b := range backlog {
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b(ctx)
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}
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}
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func (cs *CallbackSerializer) fetchPendingCallbacks() []func(context.Context) {
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var backlog []func(context.Context)
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for {
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select {
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case b := <-cs.callbacks.Get():
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backlog = append(backlog, b.(func(context.Context)))
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cs.callbacks.Load()
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default:
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return backlog
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}
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}
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}
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// Done returns a channel that is closed after the context passed to
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// NewCallbackSerializer is canceled and all callbacks have been executed.
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func (cs *CallbackSerializer) Done() <-chan struct{} {
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return cs.done
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}
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