org.springframework.batch.poller.DirectPoller Maven / Gradle / Ivy
/*
* Copyright 2006-2010 the original author or authors.
*
* Licensed 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
*
* https://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.springframework.batch.poller;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
/**
* A {@link Poller} that uses the callers thread to poll for a result as soon as
* it is asked for. This is often appropriate if you expect a result relatively
* quickly, or if there is only one such result expected (otherwise it is more
* efficient to use a background thread to do the polling).
*
* @author Dave Syer
*
* @param the type of the result
*/
public class DirectPoller implements Poller {
private final long interval;
public DirectPoller(long interval) {
this.interval = interval;
}
/**
* Get a future for a non-null result from the callback. Only when the
* result is asked for (using {@link Future#get()} or
* {@link Future#get(long, TimeUnit)} will the polling actually start.
*
* @see Poller#poll(Callable)
*/
@Override
public Future poll(Callable callable) throws Exception {
return new DirectPollingFuture(interval, callable);
}
private static class DirectPollingFuture implements Future {
private final long startTime = System.currentTimeMillis();
private volatile boolean cancelled;
private volatile S result = null;
private final long interval;
private final Callable callable;
public DirectPollingFuture(long interval, Callable callable) {
this.interval = interval;
this.callable = callable;
}
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
cancelled = true;
return true;
}
@Override
public S get() throws InterruptedException, ExecutionException {
try {
return get(-1, TimeUnit.MILLISECONDS);
}
catch (TimeoutException e) {
throw new IllegalStateException("Unexpected timeout waiting for result", e);
}
}
@Override
public S get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
try {
result = callable.call();
}
catch (Exception e) {
throw new ExecutionException(e);
}
Long nextExecutionTime = startTime + interval;
long currentTimeMillis = System.currentTimeMillis();
long timeoutMillis = TimeUnit.MILLISECONDS.convert(timeout, unit);
while (result == null && !cancelled) {
long delta = nextExecutionTime - startTime;
if (delta >= timeoutMillis && timeoutMillis > 0) {
throw new TimeoutException("Timed out waiting for task to return non-null result");
}
if (nextExecutionTime > currentTimeMillis) {
Thread.sleep(nextExecutionTime - currentTimeMillis);
}
currentTimeMillis = System.currentTimeMillis();
nextExecutionTime = currentTimeMillis + interval;
try {
result = callable.call();
}
catch (Exception e) {
throw new ExecutionException(e);
}
}
return result;
}
@Override
public boolean isCancelled() {
return cancelled;
}
@Override
public boolean isDone() {
return cancelled || result != null;
}
}
}