/*
    * Copyright (C) 2010 The Guava Authors
    *
    * 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.google.common.util.concurrent;
  
  import static java.util.logging.Level.SEVERE;
  
  import com.google.common.annotations.VisibleForTesting;
  
  import java.lang.Thread.UncaughtExceptionHandler;
  import java.util.logging.Logger;
  
  /**
   * Factories for {@link UncaughtExceptionHandler} instances.
   *
   * @author Gregory Kick
   * @since 8.0
   */
  public final class UncaughtExceptionHandlers {
    private UncaughtExceptionHandlers() {}
  
    /**
     * Returns an exception handler that exits the system. This is particularly useful for the main
     * thread, which may start up other, non-daemon threads, but fail to fully initialize the
     * application successfully.
     *
     * <p>Example usage:
     * <pre>public static void main(String[] args) {
     *   Thread.currentThread().setUncaughtExceptionHandler(UncaughtExceptionHandlers.systemExit());
     *   ...
     * </pre>
     *
     * <p>The returned handler logs any exception at severity {@code SEVERE} and then shuts down the
     * process with an exit status of 1, indicating abnormal termination.
     */
    public static UncaughtExceptionHandler systemExit() {
      return new Exiter(Runtime.getRuntime());
    }
  
    @VisibleForTesting static final class Exiter implements UncaughtExceptionHandler {
      private static final Logger logger = Logger.getLogger(Exiter.class.getName());
  
      private final Runtime runtime;
  
      Exiter(Runtime runtime) {
        this.runtime = runtime;
      }
  
      @Override public void uncaughtException(Thread t, Throwable e) {
        try {
          // cannot use FormattingLogger due to a dependency loop
          logger.log(SEVERE, String.format("Caught an exception in %s.  Shutting down.", t), e);
        } catch (Throwable errorInLogging) {
          // If logging fails, e.g. due to missing memory, at least try to log the
          // message and the cause for the failed logging.
          System.err.println(e.getMessage());
          System.err.println(errorInLogging.getMessage());
        } finally {
          runtime.exit(1);
        }
      }
    }
  }