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S'abonner avec le contrôle de flux

Crée un abonné avec des paramètres de contrôle de flux et reçoit des messages.

Pages de documentation incluant cet exemple de code

Pour afficher l'exemple de code utilisé en contexte, consultez la documentation suivante :

Exemple de code

C#

Avant d'essayer cet exemple, suivez les instructions de configuration de C# décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour C#. 


using Google.Api.Gax;
using Google.Cloud.PubSub.V1;
using System;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

public class PullMessagesWithFlowControlAsyncSample
{
    public async Task<int> PullMessagesWithFlowControlAsync(string projectId, string subscriptionId, bool acknowledge)
    {
        SubscriptionName subscriptionName = SubscriptionName.FromProjectSubscription(projectId, subscriptionId);
        int messageCount = 0;
        SubscriberClient subscriber = await SubscriberClient.CreateAsync(subscriptionName,
            settings: new SubscriberClient.Settings()
            {
                AckExtensionWindow = TimeSpan.FromSeconds(4),
                AckDeadline = TimeSpan.FromSeconds(10),
                FlowControlSettings = new FlowControlSettings(maxOutstandingElementCount: 100, maxOutstandingByteCount: 10240)
            });
        // SubscriberClient runs your message handle function on multiple
        // threads to maximize throughput.
        Task startTask = subscriber.StartAsync((PubsubMessage message, CancellationToken cancel) =>
        {
            string text = Encoding.UTF8.GetString(message.Data.ToArray());
            Console.WriteLine($"Message {message.MessageId}: {text}");
            Interlocked.Increment(ref messageCount);
            return Task.FromResult(acknowledge ? SubscriberClient.Reply.Ack : SubscriberClient.Reply.Nack);
        });
        // Run for 5 seconds.
        await Task.Delay(5000);
        await subscriber.StopAsync(CancellationToken.None);
        // Lets make sure that the start task finished successfully after the call to stop.
        await startTask;
        return messageCount;
    }
}

C++

Avant d'essayer cet exemple, suivez les instructions de configuration de C++ décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour C++. 

namespace pubsub = google::cloud::pubsub;
using google::cloud::future;
using google::cloud::StatusOr;
[](std::string project_id, std::string subscription_id) {
  // Change the flow control watermarks, by default the client library uses
  // 0 and 1,000 for the message count watermarks, and 0 and 10MiB for the
  // size watermarks. Recall that the library stops requesting messages if
  // any of the high watermarks are reached, and the library resumes
  // requesting messages when *both* low watermarks are reached.
  auto constexpr kMiB = 1024 * 1024L;
  auto subscriber = pubsub::Subscriber(pubsub::MakeSubscriberConnection(
      pubsub::Subscription(std::move(project_id), std::move(subscription_id)),
      pubsub::SubscriberOptions{}
          .set_max_outstanding_messages(1000)
          .set_max_outstanding_bytes(8 * kMiB)));

  std::mutex mu;
  std::condition_variable cv;
  int count = 0;
  auto constexpr kExpectedMessageCount = 4;
  auto handler = [&](pubsub::Message const& m, pubsub::AckHandler h) {
    std::move(h).ack();
    {
      std::lock_guard<std::mutex> lk(mu);
      std::cout << "Received message [" << count << "] " << m.data() << "\n";
      if (++count < kExpectedMessageCount) return;
    }
    cv.notify_one();
  };
  auto session = subscriber.Subscribe(std::move(handler));
  {
    std::unique_lock<std::mutex> lk(mu);
    cv.wait(lk, [&] { return count >= kExpectedMessageCount; });
  }
  session.cancel();
  auto status = session.get();
  std::cout << "Message count: " << count << ", status: " << status << "\n";
}

Go

Avant d'essayer cet exemple, suivez les instructions de configuration de Go décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour Go. 

import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/pubsub"
)

func pullMsgsSettings(w io.Writer, projectID, subID string) error {
	// projectID := "my-project-id"
	// subID := "my-sub"
	ctx := context.Background()
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("pubsub.NewClient: %v", err)
	}

	sub := client.Subscription(subID)
	sub.ReceiveSettings.Synchronous = true
	// MaxOutstandingMessages is the maximum number of unprocessed messages the
	// client will pull from the server before pausing.
	//
	// This is only guaranteed when ReceiveSettings.Synchronous is set to true.
	// When Synchronous is set to false, the StreamingPull RPC is used which
	// can pull a single large batch of messages at once that is greater than
	// MaxOustandingMessages before pausing. For more info, see
	// https://cloud.google.com/pubsub/docs/pull#streamingpull_dealing_with_large_backlogs_of_small_messages.
	sub.ReceiveSettings.MaxOutstandingMessages = 10
	// MaxOutstandingBytes is the maximum size of unprocessed messages,
	// that the client will pull from the server before pausing. Similar
	// to MaxOutstandingMessages, this may be exceeded with a large batch
	// of messages since we cannot control the size of a batch of messages
	// from the server (even with the synchronous Pull RPC).
	sub.ReceiveSettings.MaxOutstandingBytes = 1e10
	err = sub.Receive(ctx, func(ctx context.Context, msg *pubsub.Message) {
		fmt.Fprintf(w, "Got message: %q\n", string(msg.Data))
		msg.Ack()
	})
	if err != nil {
		return fmt.Errorf("Receive: %v", err)
	}
	return nil
}

Java

Avant d'essayer cet exemple, suivez les instructions de configuration de Java décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour Java. 


import com.google.api.gax.batching.FlowControlSettings;
import com.google.cloud.pubsub.v1.AckReplyConsumer;
import com.google.cloud.pubsub.v1.MessageReceiver;
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.PubsubMessage;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

public class SubscribeWithFlowControlSettingsExample {
  public static void main(String... args) throws Exception {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "your-project-id";
    String subscriptionId = "your-subscription-id";

    subscribeWithFlowControlSettingsExample(projectId, subscriptionId);
  }

  public static void subscribeWithFlowControlSettingsExample(
      String projectId, String subscriptionId) {
    ProjectSubscriptionName subscriptionName =
        ProjectSubscriptionName.of(projectId, subscriptionId);

    // Instantiate an asynchronous message receiver.
    MessageReceiver receiver =
        (PubsubMessage message, AckReplyConsumer consumer) -> {
          // Handle incoming message, then ack the received message.
          System.out.println("Id: " + message.getMessageId());
          System.out.println("Data: " + message.getData().toStringUtf8());
          consumer.ack();
        };

    Subscriber subscriber = null;

    // The subscriber will pause the message stream and stop receiving more messsages from the
    // server if any one of the conditions is met.
    FlowControlSettings flowControlSettings =
        FlowControlSettings.newBuilder()
            // 1,000 outstanding messages. Must be >0. It controls the maximum number of messages
            // the subscriber receives before pausing the message stream.
            .setMaxOutstandingElementCount(1000L)
            // 100 MiB. Must be >0. It controls the maximum size of messages the subscriber
            // receives before pausing the message stream.
            .setMaxOutstandingRequestBytes(100L * 1024L * 1024L)
            .build();

    try {
      subscriber =
          Subscriber.newBuilder(subscriptionName, receiver)
              .setFlowControlSettings(flowControlSettings)
              .build();

      // Start the subscriber.
      subscriber.startAsync().awaitRunning();
      System.out.printf("Listening for messages on %s:\n", subscriptionName.toString());
      // Allow the subscriber to run for 30s unless an unrecoverable error occurs.
      subscriber.awaitTerminated(30, TimeUnit.SECONDS);
    } catch (TimeoutException timeoutException) {
      // Shut down the subscriber after 30s. Stop receiving messages.
      subscriber.stopAsync();
    }
  }
}

Node.js

Avant d'essayer cet exemple, suivez les instructions de configuration de Node.js décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour Node.js. 

/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const subscriptionName = 'YOUR_SUBSCRIPTION_NAME';
// const maxInProgress = 5;
// const timeout = 10;

// Imports the Google Cloud client library
const {PubSub} = require('@google-cloud/pubsub');

// Creates a client; cache this for further use
const pubSubClient = new PubSub();

async function subscribeWithFlowControlSettings() {
  const subscriberOptions = {
    flowControl: {
      maxMessages: maxInProgress,
    },
  };

  // References an existing subscription.
  // Note that flow control settings are not persistent across subscribers.
  const subscription = pubSubClient.subscription(
    subscriptionName,
    subscriberOptions
  );

  console.log(
    `Subscriber to subscription ${subscription.name} is ready to receive messages at a controlled volume of ${maxInProgress} messages.`
  );

  const messageHandler = message => {
    console.log(`Received message: ${message.id}`);
    console.log(`\tData: ${message.data}`);
    console.log(`\tAttributes: ${message.attributes}`);

    // "Ack" (acknowledge receipt of) the message
    message.ack();
  };

  subscription.on('message', messageHandler);

  setTimeout(() => {
    subscription.close();
  }, timeout * 1000);
}

Python

Avant d'essayer cet exemple, suivez les instructions de configuration de Python décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour Python. 

from concurrent.futures import TimeoutError
from google.cloud import pubsub_v1

# TODO(developer)
# project_id = "your-project-id"
# subscription_id = "your-subscription-id"
# Number of seconds the subscriber should listen for messages
# timeout = 5.0

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path(project_id, subscription_id)

def callback(message):
    print(f"Received {message.data}.")
    message.ack()

# Limit the subscriber to only have ten outstanding messages at a time.
flow_control = pubsub_v1.types.FlowControl(max_messages=10)

streaming_pull_future = subscriber.subscribe(
    subscription_path, callback=callback, flow_control=flow_control
)
print(f"Listening for messages on {subscription_path}..\n")

# Wrap subscriber in a 'with' block to automatically call close() when done.
with subscriber:
    try:
        # When `timeout` is not set, result() will block indefinitely,
        # unless an exception is encountered first.
        streaming_pull_future.result(timeout=timeout)
    except TimeoutError:
        streaming_pull_future.cancel()

Ruby

Avant d'essayer cet exemple, suivez les instructions de configuration de Ruby décrites dans le Guide de démarrage rapide de Pub/Sub – Utiliser des bibliothèques clientes. Pour en savoir plus, consultez la documentation de référence sur l'API Pub/Sub pour Ruby. 

# subscription_name = "Your Pubsub subscription name"
require "google/cloud/pubsub"

pubsub = Google::Cloud::Pubsub.new

subscription = pubsub.subscription subscription_name
subscriber   = subscription.listen inventory: 10 do |received_message|
  puts "Received message: #{received_message.data}"
  received_message.acknowledge!
end

subscriber.start
# Let the main thread sleep for 60 seconds so the thread for listening
# messages does not quit
sleep 60
subscriber.stop.wait!