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* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.client;
import org.apache.http.client.methods.AbstractExecutionAwareRequest;
import org.apache.http.client.methods.HttpRequestBase;
import java.util.concurrent.CancellationException;
/**
* Represents an operation that can be cancelled.
* Returned when executing async requests through {@link RestClient#performRequestAsync(Request, ResponseListener)}, so that the request
* can be cancelled if needed. Cancelling a request will result in calling {@link AbstractExecutionAwareRequest#abort()} on the underlying
* request object, which will in turn cancel its corresponding {@link java.util.concurrent.Future}.
* Note that cancelling a request does not automatically translate to aborting its execution on the server side, which needs to be
* specifically implemented in each API.
*/
public class Cancellable {
static final Cancellable NO_OP = new Cancellable(null) {
@Override
public void cancel() {
}
@Override
void runIfNotCancelled(Runnable runnable) {
throw new UnsupportedOperationException();
}
};
static Cancellable fromRequest(HttpRequestBase httpRequest) {
return new Cancellable(httpRequest);
}
private final HttpRequestBase httpRequest;
private Cancellable(HttpRequestBase httpRequest) {
this.httpRequest = httpRequest;
}
/**
* Cancels the on-going request that is associated with the current instance of {@link Cancellable}.
*
*/
public synchronized void cancel() {
this.httpRequest.abort();
}
/**
* Executes some arbitrary code iff the on-going request has not been cancelled, otherwise throws {@link CancellationException}.
* This is needed to guarantee that cancelling a request works correctly even in case {@link #cancel()} is called between different
* attempts of the same request. The low-level client reuses the same instance of the {@link AbstractExecutionAwareRequest} by calling
* {@link AbstractExecutionAwareRequest#reset()} between subsequent retries. The {@link #cancel()} method can be called at anytime,
* and we need to handle the case where it gets called while there is no request being executed as one attempt may have failed and
* the subsequent attempt has not been started yet.
* If the request has already been cancelled we don't go ahead with the next attempt, and artificially raise the
* {@link CancellationException}, otherwise we run the provided {@link Runnable} which will reset the request and send the next attempt.
* Note that this method must be synchronized as well as the {@link #cancel()} method, to prevent a request from being cancelled
* when there is no future to cancel, which would make cancelling the request a no-op.
*/
synchronized void runIfNotCancelled(Runnable runnable) {
if (this.httpRequest.isAborted()) {
throw newCancellationException();
}
runnable.run();
}
static CancellationException newCancellationException() {
return new CancellationException("request was cancelled");
}
}