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    • io.rsocket.internal.UnicastMonoEmpty Maven / Gradle / Ivy

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    package io.rsocket.internal;

import java.time.Duration;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import reactor.core.CoreSubscriber;
import reactor.core.Scannable;
import reactor.core.publisher.Mono;
import reactor.core.publisher.Operators;
import reactor.util.annotation.Nullable;

/**
 * Represents an empty publisher which only calls onSubscribe and onComplete and allows only a
 * single subscriber.
 *
 * @see Reactive-Streams-Commons
 */
public final class UnicastMonoEmpty extends Mono implements Scannable {

  final Runnable onSubscribe;

  volatile int once;

  @SuppressWarnings("rawtypes")
  static final AtomicIntegerFieldUpdater ONCE =
      AtomicIntegerFieldUpdater.newUpdater(UnicastMonoEmpty.class, "once");

  UnicastMonoEmpty(Runnable onSubscribe) {
    this.onSubscribe = onSubscribe;
  }

  @Override
  public void subscribe(CoreSubscriber actual) {
    if (once == 0 && ONCE.compareAndSet(this, 0, 1)) {
      onSubscribe.run();
      Operators.complete(actual);
    } else {
      Operators.error(
          actual, new IllegalStateException("UnicastMonoEmpty allows only a single Subscriber"));
    }
  }

  /**
   * Returns a properly parametrized instance of this empty Publisher.
   *
   * @param  the output type
   * @return a properly parametrized instance of this empty Publisher
   */
  @SuppressWarnings("unchecked")
  public static  Mono newInstance(Runnable onSubscribe) {
    return (Mono) new UnicastMonoEmpty(onSubscribe);
  }

  @Override
  @Nullable
  public Object block(Duration m) {
    if (once == 0 && ONCE.compareAndSet(this, 0, 1)) {
      onSubscribe.run();
      return null;
    } else {
      throw new IllegalStateException("UnicastMonoEmpty allows only a single Subscriber");
    }
  }

  @Override
  @Nullable
  public Object block() {
    if (once == 0 && ONCE.compareAndSet(this, 0, 1)) {
      onSubscribe.run();
      return null;
    } else {
      throw new IllegalStateException("UnicastMonoEmpty allows only a single Subscriber");
    }
  }

  @Override
  public Object scanUnsafe(Attr key) {
    return null; // no particular key to be represented, still useful in hooks
  }

  @Override
  public String stepName() {
    return "source(UnicastMonoEmpty)";
  }
}
    
    
    
    

    




    
    
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