com.salesforce.reactivegrpc.common

Class AbstractSubscriberAndProducer<T>

java.lang.Object

com.salesforce.reactivegrpc.common.AbstractSubscriberAndProducer<T>

Type Parameters:

T - T

All Implemented Interfaces:

Runnable, org.reactivestreams.Subscriber<T>

Direct Known Subclasses:

AbstractSubscriberAndClientProducer, AbstractSubscriberAndServerProducer

public abstract class AbstractSubscriberAndProducer<T>
extends Object
implements org.reactivestreams.Subscriber<T>, Runnable

ReactivePublisherBackpressureOnReadyHandler bridges the manual flow control idioms of Reactive Streams and gRPC. This class takes messages off of a Publisher and feeds them into a CallStreamObserver while respecting backpressure. This class is the inverse of AbstractStreamObserverAndPublisher.

When a gRPC publisher's transport wants more data to transmit, the CallStreamObserver's onReady handler is signaled. This handler must keep transmitting messages until CallStreamObserver.isReady() ceases to be true.

When a Publisher is subscribed to by a Subscriber, the Publisher hands the Subscriber a Subscription. When the Subscriber wants more messages from the Publisher, the Subscriber calls Subscription.request(long).

To bridge the two idioms: when gRPC wants more messages, the onReadyHandler is called and run() calls the Subscription's request() method, asking the Publisher to produce another message. Since this class is also registered as the Publisher's Subscriber, the onNext(Object) method is called. onNext() passes the message to gRPC's StreamObserver.onNext(Object) method, and then calls request() again if CallStreamObserver.isReady() is true. The loop of request→pass→check is repeated until isReady() returns false, indicating that the outbound transmit buffer is full and that backpressure must be applied.

Field Summary

Fields

Modifier and Type	Field and Description
protected io.grpc.stub.CallStreamObserver<T>	downstream

Constructor Summary

Constructors

Constructor and Description
AbstractSubscriberAndProducer()

Method Summary

Modifier and Type	Method and Description
void	cancel()
protected abstract org.reactivestreams.Subscription	fuse(org.reactivestreams.Subscription subscription)
boolean	isCanceled()
void	onComplete()
void	onError(Throwable t)
void	onNext(T t)
void	onSubscribe(org.reactivestreams.Subscription subscription)
protected Throwable	prepareError(Throwable throwable)
void	run()
void	subscribe(io.grpc.stub.CallStreamObserver<T> downstream)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

downstream

protected volatile io.grpc.stub.CallStreamObserver<T> downstream

Constructor Detail

AbstractSubscriberAndProducer

public AbstractSubscriberAndProducer()

Method Detail

subscribe

public void subscribe(io.grpc.stub.CallStreamObserver<T> downstream)

run

public void run()

Specified by:

run in interface Runnable

cancel

public void cancel()

isCanceled

public boolean isCanceled()

onSubscribe

public void onSubscribe(org.reactivestreams.Subscription subscription)

Specified by:

onSubscribe in interface org.reactivestreams.Subscriber<T>

onNext

public void onNext(T t)

Specified by:

onNext in interface org.reactivestreams.Subscriber<T>

onError

public void onError(Throwable t)

Specified by:

onError in interface org.reactivestreams.Subscriber<T>

onComplete

public void onComplete()

Specified by:

onComplete in interface org.reactivestreams.Subscriber<T>

fuse

protected abstract org.reactivestreams.Subscription fuse(org.reactivestreams.Subscription subscription)

prepareError

protected Throwable prepareError(Throwable throwable)