Java Concurrency in Practice——LogService

书中的List7.15的代码给出的在多线程中，producer-consumer模型下，如何有效的终止服务的实现方式。在示例代码中，利用reservations来表明还有多少的消息需要取出来，并利用isShutdown来表明服务是否已经终止，通过确保isShutdown和reservations的改变是原子的，来获得整个服务的线程安全。

public class LogService {
		private final BlockingQueue<String> queue;
		private final LoggerThread loggerThread;
		private final PrintWriter writer;
		@GuardedBy("this")
		private boolean isShutdown;
		@GuardedBy("this")
		private int reservations;

		public void start() {
			loggerThread.start();
		}

		public void stop() {
			synchronized (this) {
				isShutdown = true;
			}
			loggerThread.interrupt();
		}

		public void log(String msg) throws InterruptedException {
		synchronized (this) {
		if (isShutdown)
		throw new IllegalStateException(...);
		++reservations;
		}
		queue.put(msg);
		}

		private class LoggerThread extends Thread {
			public void run() {
				try {
					while (true) {
						try {
							synchronized (LogService.this) {
								if (isShutdown && reservations == 0)
									break;
							}
							String msg = queue.take();
							synchronized (LogService.this) {
								--reservations;
							}
							writer.println(msg);
						} catch (InterruptedException e) {
							/* retry */ }
					}
				} finally {
					writer.close();
				}
			}
		}
	}