Struct MaxOutstandingMessagesOption (2.21.0-rc)

The maximum number of outstanding messages per streaming pull.

The Cloud Pub/Sub C++ client library uses streaming pull requests to receive messages from the service. The service will stop delivering messages if this many messages or more have neither been acknowledged nor rejected.

If a negative or 0 value is supplied, the number of messages will be unlimited.

  namespace pubsub = ::google::cloud::pubsub;
  using ::google::cloud::future;
  using ::google::cloud::Options;
  using ::google::cloud::StatusOr;
  auto sample = [](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)),
            .set<pubsub::MaxOutstandingBytesOption>(8 * kMiB)));

    auto session = subscriber.Subscribe(
        [](pubsub::Message const& m, pubsub::AckHandler h) {
          std::cout << "Received message " << m << "\n";
    return std::make_pair(subscriber, std::move(session));

Type Aliases


Alias Of: std::int64_t