001/*
002 * Copyright (C) 2010 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.util.concurrent;
016
017import static java.util.logging.Level.SEVERE;
018
019import com.google.common.annotations.GwtIncompatible;
020import com.google.common.annotations.VisibleForTesting;
021import java.lang.Thread.UncaughtExceptionHandler;
022import java.util.Locale;
023import java.util.logging.Logger;
024
025/**
026 * Factories for {@link UncaughtExceptionHandler} instances.
027 *
028 * @author Gregory Kick
029 * @since 8.0
030 */
031@GwtIncompatible
032@ElementTypesAreNonnullByDefault
033public final class UncaughtExceptionHandlers {
034  private UncaughtExceptionHandlers() {}
035
036  /**
037   * Returns an exception handler that exits the system. This is particularly useful for the main
038   * thread, which may start up other, non-daemon threads, but fail to fully initialize the
039   * application successfully.
040   *
041   * <p>Example usage:
042   *
043   * <pre>
044   * public static void main(String[] args) {
045   *   Thread.currentThread().setUncaughtExceptionHandler(UncaughtExceptionHandlers.systemExit());
046   *   ...
047   * </pre>
048   *
049   * <p>The returned handler logs any exception at severity {@code SEVERE} and then shuts down the
050   * process with an exit status of 1, indicating abnormal termination.
051   */
052  public static UncaughtExceptionHandler systemExit() {
053    return new Exiter(Runtime.getRuntime());
054  }
055
056  @VisibleForTesting
057  static final class Exiter implements UncaughtExceptionHandler {
058    private static final Logger logger = Logger.getLogger(Exiter.class.getName());
059
060    private final Runtime runtime;
061
062    Exiter(Runtime runtime) {
063      this.runtime = runtime;
064    }
065
066    @Override
067    public void uncaughtException(Thread t, Throwable e) {
068      try {
069        logger.log(
070            SEVERE, String.format(Locale.ROOT, "Caught an exception in %s.  Shutting down.", t), e);
071      } catch (RuntimeException | Error errorInLogging) {
072        // If logging fails, e.g. due to missing memory, at least try to log the
073        // message and the cause for the failed logging.
074        System.err.println(e.getMessage());
075        System.err.println(errorInLogging.getMessage());
076      } finally {
077        runtime.exit(1);
078      }
079    }
080  }
081}