lidavidm commented on a change in pull request #8476: URL: https://github.com/apache/arrow/pull/8476#discussion_r507710515
########## File path: java/flight/flight-core/src/main/java/org/apache/arrow/flight/BackpressureStrategy.java ########## @@ -0,0 +1,113 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.arrow.flight; + +import org.apache.arrow.vector.VectorSchemaRoot; + +import com.google.common.base.Preconditions; + +/** + * Helper interface to dynamically handle backpressure when implementing FlightProducers. + */ +public interface BackpressureStrategy { + /** + * The state of the client after a call to waitForListener. + */ + enum WaitResult { + /** + * Listener is ready. + */ + READY, + + /** + * Listener was cancelled by the client. + */ + CANCELLED, + + /** + * Timed out waiting for the listener to change state. + */ + TIMEOUT + } + + /** + * Set up operations to work against the given listener. + * + * This must be called exactly once and before any calls to {@link #waitForListener(long)} and + * {@link OutboundStreamListener#start(VectorSchemaRoot)} + * @param listener The listener this strategy applies to. + */ + void register(FlightProducer.ServerStreamListener listener); + + /** + * Waits for the listener to be ready or cancelled up to the given timeout. + * + * @param timeout The timeout in milliseconds. Infinite if timeout is <= 0. + * @return The result of the wait. + */ + WaitResult waitForListener(long timeout); + + /** + * A back pressure strategy that uses callbacks to notify when the client is ready or cancelled. + */ + class CallbackBackpressureStrategy implements BackpressureStrategy { + private final Object lock = new Object(); + private FlightProducer.ServerStreamListener listener; + + @Override + public void register(FlightProducer.ServerStreamListener listener) { + this.listener = listener; + listener.setOnReadyHandler(this::onReadyOrCancel); + listener.setOnCancelHandler(this::onReadyOrCancel); + } + + @Override + public WaitResult waitForListener(long timeout) { + Preconditions.checkNotNull(listener); + final long startTime = System.currentTimeMillis(); + synchronized (lock) { + while (!listener.isReady() && !listener.isCancelled()) { + try { + lock.wait(timeout); + if (System.currentTimeMillis() > startTime + timeout) { + return WaitResult.TIMEOUT; + } + } catch (InterruptedException ex) { + Thread.currentThread().interrupt(); + return WaitResult.CANCELLED; + } + } + + if (listener.isReady()) { + return WaitResult.READY; + } else if (listener.isCancelled()) { + return WaitResult.CANCELLED; + } else if (System.currentTimeMillis() > startTime + timeout) { + return WaitResult.TIMEOUT; + } + throw new RuntimeException("Invalid state when waiting for listener."); Review comment: Ah yes, you're right. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
