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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.concurrent;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
* An executor that will first try a bounded cached thread pool before falling back to an unbounded
* single threaded thread pool that will take over dispatching to the primary pool.
*/
public class CachedThreadPoolWithFallback implements AutoCloseable, Executor {
private final ExecutorService primary;
private final ExecutorService secondary;
public CachedThreadPoolWithFallback(String baseName, int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit timeUnit) {
primary = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, timeUnit,
new SynchronousQueue<>(), ThreadFactoryFactory.getDaemonThreadFactory(baseName + ".primary"));
secondary = Executors.newSingleThreadExecutor(ThreadFactoryFactory.getDaemonThreadFactory(baseName + ".secondary"));
}
@Override
public void execute(Runnable command) {
try {
primary.execute(command);
} catch (RejectedExecutionException e1) {
secondary.execute(() -> retryForever(command));
}
}
private void retryForever(Runnable command) {
while (true) {
try {
primary.execute(command);
return;
} catch (RejectedExecutionException rejected) {
try {
Thread.sleep(1);
} catch (InterruptedException silenced) { }
}
}
}
@Override
public void close() {
secondary.shutdown();
join(secondary);
primary.shutdown();
join(primary);
}
private static void join(ExecutorService executor) {
while (true) {
try {
if (executor.awaitTermination(60, TimeUnit.SECONDS)) {
return;
}
} catch (InterruptedException e) {}
}
}
}
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