lostluck commented on code in PR #17955: URL: https://github.com/apache/beam/pull/17955#discussion_r894828559
########## sdks/go/examples/native_wordcap/nativepubsubio/native.go: ########## @@ -0,0 +1,247 @@ +// Licensed to the Apache Software Foundation (ASF) under one or more +// contributor license agreements. See the NOTICE file distributed with +// this work for additional information regarding copyright ownership. +// The ASF licenses this file to You 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 nativepubsubio contains a Golang implementation of streaming reads +// and writes to PubSub. This is not as fully featured as the cross-language +// pubsubio package present in the Beam Go repository and should not be used +// in place of it. +package nativepubsubio + +import ( + "context" + "errors" + "fmt" + "time" + + "cloud.google.com/go/pubsub" + "github.com/apache/beam/sdks/v2/go/pkg/beam" + "github.com/apache/beam/sdks/v2/go/pkg/beam/core/sdf" + "github.com/apache/beam/sdks/v2/go/pkg/beam/log" + "github.com/apache/beam/sdks/v2/go/pkg/beam/register" + "github.com/apache/beam/sdks/v2/go/pkg/beam/util/pubsubx" +) + +func init() { + register.DoFn5x2[context.Context, beam.BundleFinalization, *sdf.LockRTracker, []byte, func(beam.EventTime, []byte), sdf.ProcessContinuation, error](&pubSubRead{}) + register.DoFn2x1[context.Context, []byte, error](&pubSubWrite{}) + register.Emitter2[beam.EventTime, []byte]() +} + +// pubSubRead is a structural DoFn representing a read from a given subscription ID. +type pubSubRead struct { + ProjectID string + Subscription string + client *pubsub.Client + processedMessages []*pubsub.Message +} + +// newPubSubRead inserts an unbounded read from a PubSub topic into the pipeline. If an existing subscription +// is provided, the DoFn will read using that subscription; otherwise, a new subscription to the topic +// will be created using the provided subscription name. +func newPubSubRead(ctx context.Context, projectID, topic, subscription string) (*pubSubRead, error) { + if topic == "" { + return nil, errors.New("please provide either a topic to read from") + } + client, err := pubsub.NewClient(ctx, projectID) + if err != nil { + return nil, err + } + + top := client.Topic(topic) + if ok, err := top.Exists(ctx); !ok || err != nil { + return nil, fmt.Errorf("failed to get topic; exists: %v, error: %v", ok, err) + } + sub, err := pubsubx.EnsureSubscription(ctx, client, topic, subscription) + if err != nil { + return nil, err + } + return &pubSubRead{ProjectID: projectID, Subscription: sub.ID()}, nil +} + +// CreateInitialRestriction() establishes the PubSub subscription ID as the +// initial restriction +func (r *pubSubRead) CreateInitialRestriction(_ []byte) string { + return r.Subscription +} + +// CreateTracker wraps the PubSub subscription ID in a StaticRTracker +// and applies a mutex via LockRTracker. +func (r *pubSubRead) CreateTracker(rest string) *sdf.LockRTracker { + return sdf.NewLockRTracker(NewSubscriptionRTracker(rest)) +} + +// RestrictionSize always returns 1.0, as the restriction is always 1 subscription. +func (r *pubSubRead) RestrictionSize(_ []byte, rest string) float64 { + return 1.0 +} + +// SplitRestriction is a no-op as the restriction cannot be split. +func (r *pubSubRead) SplitRestriction(_ []byte, rest string) []string { + return []string{rest} +} + +// Setup initializes a PubSub client if one has not been created already +func (r *pubSubRead) Setup(ctx context.Context) error { + if r.client == nil { + client, err := pubsub.NewClient(context.Background(), r.ProjectID) + if err != nil { + return err + } + r.client = client + } + return nil +} + +var messageTimeout time.Duration = 5 * time.Second + +// ProcessElement initializes a PubSub client if one has not been created already, reads from the PubSub subscription, +// and emits elements as it reads them. If no messages are available, the DoFn will schedule itself to resume processing +// later. If polling the subscription returns an error, the error will be logged and the DoFn will not reschedule itself. +func (r *pubSubRead) ProcessElement(ctx context.Context, bf beam.BundleFinalization, rt *sdf.LockRTracker, _ []byte, emit func(beam.EventTime, []byte)) (sdf.ProcessContinuation, error) { + // Register finalization callback + bf.RegisterCallback(5*time.Minute, func() error { + for _, m := range r.processedMessages { + m.Ack() + } + r.processedMessages = nil + return nil + }) + + for { + ok := rt.TryClaim(r.Subscription) + if !ok { + return sdf.ResumeProcessingIn(5 * time.Second), nil + } + sub := r.client.Subscription(r.Subscription) + ctx, cFn := context.WithCancel(ctx) + + // Because emitters are not thread safe and synchronous Receive() behavior + // is deprecated, we have to collect messages in a goroutine and pipe them + // out through a channel. + messChan := make(chan *pubsub.Message, 1) Review Comment: No action required, I just had to confirm to myself that the "comma ok" channel receive was still blocking. It is, so this is fantastic. https://go.dev/play/p/p93DFrK4DCA -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
