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/*
* Copyright 2015 Open Networking Laboratory
*
* 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
*
* 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.onlab.util;
import com.google.common.collect.Lists;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
/**
* Base implementation of an item accumulator. It allows triggering based on
* item inter-arrival time threshold, maximum batch life threshold and maximum
* batch size.
*/
public abstract class AbstractAccumulator<T> implements Accumulator<T> {
private Logger log = LoggerFactory.getLogger(AbstractAccumulator.class);
private final Timer timer;
private final int maxItems;
private final int maxBatchMillis;
private final int maxIdleMillis;
private volatile TimerTask idleTask = new ProcessorTask();
private volatile TimerTask maxTask = new ProcessorTask();
private List<T> items = Lists.newArrayList();
/**
* Creates an item accumulator capable of triggering on the specified
* thresholds.
*
* @param timer timer to use for scheduling check-points
* @param maxItems maximum number of items to accumulate before
* processing is triggered
* @param maxBatchMillis maximum number of millis allowed since the first
* item before processing is triggered
* @param maxIdleMillis maximum number millis between items before
* processing is triggered
*/
protected AbstractAccumulator(Timer timer, int maxItems,
int maxBatchMillis, int maxIdleMillis) {
this.timer = checkNotNull(timer, "Timer cannot be null");
checkArgument(maxItems > 1, "Maximum number of items must be > 1");
checkArgument(maxBatchMillis > 0, "Maximum millis must be positive");
checkArgument(maxIdleMillis > 0, "Maximum idle millis must be positive");
this.maxItems = maxItems;
this.maxBatchMillis = maxBatchMillis;
this.maxIdleMillis = maxIdleMillis;
}
@Override
public synchronized void add(T item) {
idleTask = cancelIfActive(idleTask);
items.add(checkNotNull(item, "Item cannot be null"));
// Did we hit the max item threshold?
if (items.size() >= maxItems) {
maxTask = cancelIfActive(maxTask);
scheduleNow();
} else {
// Otherwise, schedule idle task and if this is a first item
// also schedule the max batch age task.
idleTask = schedule(maxIdleMillis);
if (items.size() == 1) {
maxTask = schedule(maxBatchMillis);
}
}
}
/**
* Finalizes the current batch, if ready, and schedules a new processor
* in the immediate future.
*/
private void scheduleNow() {
if (isReady()) {
TimerTask task = new ProcessorTask(finalizeCurrentBatch());
timer.schedule(task, 1);
}
}
/**
* Schedules a new processor task given number of millis in the future.
* Batch finalization is deferred to time of execution.
*/
private TimerTask schedule(int millis) {
TimerTask task = new ProcessorTask();
timer.schedule(task, millis);
return task;
}
/**
* Cancels the specified task if it is active.
*/
private TimerTask cancelIfActive(TimerTask task) {
if (task != null) {
task.cancel();
}
return task;
}
// Task for triggering processing of accumulated items
private class ProcessorTask extends TimerTask {
private final List<T> items;
// Creates a new processor task with deferred batch finalization.
ProcessorTask() {
this.items = null;
}
// Creates a new processor task with pre-emptive batch finalization.
ProcessorTask(List<T> items) {
this.items = items;
}
@Override
public void run() {
synchronized (AbstractAccumulator.this) {
idleTask = cancelIfActive(idleTask);
}
if (isReady()) {
try {
synchronized (AbstractAccumulator.this) {
maxTask = cancelIfActive(maxTask);
}
List<T> batch = items != null ? items : finalizeCurrentBatch();
if (!batch.isEmpty()) {
processItems(batch);
}
} catch (Exception e) {
log.warn("Unable to process batch due to", e);
}
} else {
synchronized (AbstractAccumulator.this) {
idleTask = schedule(maxIdleMillis);
}
}
}
}
// Demotes and returns the current batch of items and promotes a new one.
private synchronized List<T> finalizeCurrentBatch() {
List<T> toBeProcessed = items;
items = Lists.newArrayList();
return toBeProcessed;
}
@Override
public boolean isReady() {
return true;
}
/**
* Returns the backing timer.
*
* @return backing timer
*/
public Timer timer() {
return timer;
}
/**
* Returns the maximum number of items allowed to accumulate before
* processing is triggered.
*
* @return max number of items
*/
public int maxItems() {
return maxItems;
}
/**
* Returns the maximum number of millis allowed to expire since the first
* item before processing is triggered.
*
* @return max number of millis a batch is allowed to last
*/
public int maxBatchMillis() {
return maxBatchMillis;
}
/**
* Returns the maximum number of millis allowed to expire since the last
* item arrival before processing is triggered.
*
* @return max number of millis since the last item
*/
public int maxIdleMillis() {
return maxIdleMillis;
}
}
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