使用此关键字作为并发锁

Question

在下面的程序中，LoggerThread中的this关键字class是指LoggerThread对象还是LogService对象？从逻辑上讲，它应该引用 LogService 才能使同步工作，但从语义上讲，它似乎是指 LoggerThread。

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 (this) {
                            if (isShutdown && reservations == 0)
                                break;
                        }
                        String msg = queue.take();
                        synchronized (this) { --reservations; }
                        writer.println(msg);
                    } catch (InterruptedException e) { /* retry */ }
                }
            } finally {
                writer.close();
            }
        }
    }
}

感谢您的帮助

Answer 1

this 在 LoggerThread 方法中引用了一个 LoggerThread 实例。
LogService.this指的是外class.

isShutdown和reservations都被不同的锁同步（LoggerThread.this和LogService.this），所以@GuardedBy("this")不反映实际情况。

Answer 2

this 指的是直接封闭 class 的当前实例。 JLS #15.8.4.

Logically it should refer to LogService in order for the syncronization to work, but semantically it seems it is referring to LoggerThread.

正确。这是一个错误。

Answer 3

这段代码来自伟大的书“Java 并发实践”，清单 7.15
这是一个打字错误，在“勘误表”部分中提到：
http://jcip.net.s3-website-us-east-1.amazonaws.com/errata.html

使用此关键字作为并发锁

Using this keyword as lock in concurrency

java

concurrency

this

inner-classes