com.thebuzzmedia.exiftool.core.strategies.PoolStrategy Maven / Gradle / Ivy
/**
* Copyright 2011 The Buzz Media, LLC
* Copyright 2016 Mickael Jeanroy
*
* 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 com.thebuzzmedia.exiftool.core.strategies;
import com.thebuzzmedia.exiftool.ExecutionStrategy;
import com.thebuzzmedia.exiftool.Version;
import com.thebuzzmedia.exiftool.exceptions.PoolIOException;
import com.thebuzzmedia.exiftool.logs.Logger;
import com.thebuzzmedia.exiftool.logs.LoggerFactory;
import com.thebuzzmedia.exiftool.process.CommandExecutor;
import com.thebuzzmedia.exiftool.process.OutputHandler;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingDeque;
import static com.thebuzzmedia.exiftool.commons.lang.PreConditions.notEmpty;
/**
* Implementation of {@link ExecutionStrategy} using a pool of
* strategies.
*
* Each time {{@link #execute(CommandExecutor, String, List, OutputHandler)} method
* is called, an internal strategy from the pool is picked and return to the pool once work
* is finished.
*
* This strategy should be used in a multithreaded environment, when application need to
* extract exif data from images in parallel.
*/
public class PoolStrategy implements ExecutionStrategy {
/**
* Class Logger.
*/
private static final Logger log = LoggerFactory.getLogger(PoolStrategy.class);
/**
* Pool size (i.e number of available slot).
*/
private final int poolSize;
/**
* Pool list.
*/
private final BlockingQueue pool;
/**
* Create the pool.
*
* @param strategies Internal strategies.
* @throws NullPointerException If {@code strategies} is {@code null}.
* @throws IllegalArgumentException If {@code strategies} is empty.
*/
public PoolStrategy(Collection strategies) {
notEmpty(strategies, "Pool must not be empty");
this.poolSize = strategies.size();
this.pool = new LinkedBlockingDeque<>(strategies);
}
@Override
public void execute(CommandExecutor executor, String exifTool, List arguments, OutputHandler handler) throws IOException {
ExecutionStrategy strategy = null;
try {
strategy = this.pool.take();
strategy.execute(executor, exifTool, arguments, handler);
}
catch (InterruptedException ex) {
log.warn(ex.getMessage());
Thread.currentThread().interrupt();
}
finally {
if (strategy != null) {
this.pool.offer(strategy);
}
}
}
@Override
public boolean isRunning() {
return pool.size() < poolSize;
}
@Override
public boolean isSupported(Version version) {
for (ExecutionStrategy strategy : pool) {
if (!strategy.isSupported(version)) {
return false;
}
}
return true;
}
@Override
public void close() throws Exception {
processPool(CLOSE_EXECUTION_STRATEGY);
}
@Override
public void shutdown() throws Exception {
processPool(SHUTDOWN_EXECUTION_STRATEGY);
}
private void processPool(ExecutionStrategyFunction function) throws Exception {
List strategies = new ArrayList<>(poolSize);
// Get all strategies from the pool.
// We need to be sure that all strategies are available.
log.debug("Retrieve all pending strategies");
int added = 0;
while (added != poolSize) {
try {
added += this.pool.drainTo(strategies);
if (added < poolSize) {
ExecutionStrategy strategy = this.pool.take();
strategies.add(strategy);
added++;
}
} catch (InterruptedException ex) {
log.warn(ex.getMessage());
Thread.currentThread().interrupt();
}
}
List thrownEx = new ArrayList<>(strategies.size());
int i = 0;
for (ExecutionStrategy strategy : strategies) {
try {
function.apply(strategy, i);
} catch (Exception ex) {
log.error("Failed to process strategy #{}", i);
thrownEx.add(ex);
}
finally {
i++;
// Strategy is now available.
this.pool.offer(strategy);
}
}
if (thrownEx.size() > 0) {
throw new PoolIOException("Some strategies in the pool failed to close properly", thrownEx);
}
}
private interface ExecutionStrategyFunction {
void apply(ExecutionStrategy strategy, int i) throws Exception;
}
private static final ExecutionStrategyFunction CLOSE_EXECUTION_STRATEGY = new ExecutionStrategyFunction() {
@Override
public void apply(ExecutionStrategy strategy, int i) throws Exception {
log.debug("Closing strategy #{}", i);
strategy.close();
}
};
private static final ExecutionStrategyFunction SHUTDOWN_EXECUTION_STRATEGY = new ExecutionStrategyFunction() {
@Override
public void apply(ExecutionStrategy strategy, int i) throws Exception {
log.debug("Closing strategy #{}", i);
strategy.shutdown();
}
};
}
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