org.xbib.helianthus.common.stream.StreamWriter Maven / Gradle / Ivy

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package org.xbib.helianthus.common.stream;

import org.reactivestreams.Subscriber;

import java.util.concurrent.CompletableFuture;
import java.util.function.Supplier;

/**
 * Produces the objects to be published by a {@link StreamMessage}.
 *
 * @param  the type of the stream element
 */

public interface StreamWriter {

    /**
     * Returns {@code true} if the {@link StreamMessage} is open.
     */
    boolean isOpen();

    /**
     * Writes the specified object to the {@link StreamMessage}. The written object will be transferred to the
     * {@link Subscriber}.
     */
    boolean write(T o);

    /**
     * Writes the specified object {@link Supplier} to the {@link StreamMessage}. The object provided by the
     * {@link Supplier} will be transferred to the {@link Subscriber}.
     */
    boolean write(Supplier o);

    /**
     * Performs the specified {@code task} when there's enough demans from the {@link Subscriber}.
     *
     * @return the future that completes successfully when the {@code task} finishes or
     *         exceptionally when the {@link StreamMessage} is closed unexpectedly.
     */
    CompletableFuture onDemand(Runnable task);

    /**
     * Closes the {@link StreamMessage} successfully. {@link Subscriber#onComplete()} will be invoked to
     * signal that the {@link Subscriber} has consumed the stream completely.
     */
    void close();

    /**
     * Closes the {@link StreamMessage} exceptionally. {@link Subscriber#onError(Throwable)} will be invoked to
     * signal that the {@link Subscriber} did not consume the stream completely.
     */
    void close(Throwable cause);
}