com.google.appengine.setup.RequestThreadFactory Maven / Gradle / Ivy

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/*
 * Copyright 2022 Google LLC
 *
 * 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 com.google.appengine.setup;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.apphosting.api.ApiProxy;
import com.google.apphosting.api.ApiProxy.Environment;
import java.util.List;
import java.util.concurrent.ThreadFactory;


/**
 * Thread factory creating threads with a request specific thread local environment.
 */
public class RequestThreadFactory implements ThreadFactory {
    private final Environment requestEnvironment;

    private final Object mutex;
    private final List createdThreads;
    private volatile boolean allowNewRequestThreadCreation;

    /**
     * Create a new VmRequestThreadFactory.
     *
     * @param requestEnvironment The request environment to install on each thread.
     */
    public RequestThreadFactory(Environment requestEnvironment) {
        this.mutex = new Object();
        this.requestEnvironment = requestEnvironment;
        this.createdThreads = Lists.newLinkedList();
        this.allowNewRequestThreadCreation = true;
    }

    /**
     * Create a new {@link Thread} that executes {@code runnable} for the duration of the current
     * request. This thread will be interrupted at the end of the current request.
     *
     * @param runnable The object whose run method is invoked when this thread is started. If null,
     *                 this classes run method does nothing.
     * @throws ApiProxy.ApiProxyException If called outside of a running request.
     * @throws IllegalStateException      If called after the request thread stops.
     */
    @Override
    public Thread newThread(final Runnable runnable) {
        checkState(requestEnvironment != null,
                "Request threads can only be created within the context of a running request.");
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                if (runnable == null) {
                    return;
                }
                checkState(allowNewRequestThreadCreation,
                        "Cannot start new threads after the request thread stops.");
                ApiProxy.setEnvironmentForCurrentThread(requestEnvironment);
                runnable.run();
            }
        });
        checkState(
                allowNewRequestThreadCreation, "Cannot create new threads after the request thread stops.");
        synchronized (mutex) {
            createdThreads.add(thread);
        }
        return thread;
    }

    /**
     * Returns an immutable copy of the current request thread list.
     */
    public List getRequestThreads() {
        synchronized (mutex) {
            return ImmutableList.copyOf(createdThreads);
        }
    }
}