google.registry.util.AppEngineTimeLimiter.java Source code

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Here is the source code for google.registry.util.AppEngineTimeLimiter.java

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// Copyright 2016 The Nomulus Authors. All Rights Reserved.
//
// 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 google.registry.util;

import static com.google.appengine.api.ThreadManager.currentRequestThreadFactory;

import com.google.common.util.concurrent.SimpleTimeLimiter;
import com.google.common.util.concurrent.TimeLimiter;
import java.util.List;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * A factory for {@link TimeLimiter} instances that use request threads, which carry the namespace
 * and live only as long as the request that spawned them.
 *
 * <p>It is safe to reuse instances of this class, but there is no benefit in doing so over creating
 * a fresh instance each time.
 */
public class AppEngineTimeLimiter {

    /**
     * An {@code ExecutorService} that uses a new thread for every task.
     *
     * <p>We need to use fresh threads for each request so that we can use App Engine's request
     * threads.  If we cached these threads in a thread pool (and if we were executing on a backend,
     * where there is no time limit on requests) the caching would cause the thread to keep the task
     * that opened it alive even after returning an http response, and would also cause the namespace
     * that the original thread was created in to leak out to later reuses of the thread.
     *
     * <p>Since there are no cached resources, this class doesn't have to support being shutdown.
     */
    private static class NewRequestThreadExecutorService extends AbstractExecutorService {

        @Override
        public void execute(Runnable command) {
            currentRequestThreadFactory().newThread(command).start();
        }

        @Override
        public boolean isShutdown() {
            return false;
        }

        @Override
        public boolean isTerminated() {
            return false;
        }

        @Override
        public void shutdown() {
            throw new UnsupportedOperationException();
        }

        @Override
        public List<Runnable> shutdownNow() {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean awaitTermination(long timeout, TimeUnit unit) {
            throw new UnsupportedOperationException();
        }
    }

    public static TimeLimiter create() {
        return new SimpleTimeLimiter(new NewRequestThreadExecutorService());
    }
}