后端接口性能优化分析-程序结构优化（下）

public class NewFixedTest {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(10);
        for (int i = 0; i < Integer.MAX_VALUE; i++) {
            executor.execute(() -> {
                try {
                    Thread.sleep(10000);
                } catch (InterruptedException e) {
                    //do nothing
                }
            });
        }
    }
}

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
 at java.util.concurrent.LinkedBlockingQueue.offer(LinkedBlockingQueue.java:416)
 at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1371)
 at com.example.dto.NewFixedTest.main(NewFixedTest.java:14)

//阻塞队列是LinkedBlockingQueue，并且是使用的是无参构造函数
public static ExecutorService newFixedThreadPool(int nThreads) {
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  0L, TimeUnit.MILLISECONDS,
                                  new LinkedBlockingQueue<Runnable>());
}
//无参构造函数，默认最大容量是Integer.MAX_VALUE，相当于无界的阻塞队列的了
public LinkedBlockingQueue() {
    this(Integer.MAX_VALUE);
}

public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

future.get(1, TimeUnit.SECONDS);

@Async
public void testAsync() throws InterruptedException {
    System.out.println("处理异步任务");
    TimeUnit.SECONDS.sleep(new Random().nextInt(100));
}

public class ThreadTest {
    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executorOne = new ThreadPoolExecutor(5, 5, 1, 
                TimeUnit.MINUTES, new ArrayBlockingQueue<Runnable>(20));
        executorOne.execute(()->{
            throw new NullPointerException();
        });
    }
}

Exception in thread "pool-1-thread-1" java.lang.NullPointerException
 at com.example.dto.ThreadTest.lambda$main$0(ThreadTest.java:17)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 at java.lang.Thread.run(Thread.java:748)

public class ThreadTest {
    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executorOne = new ThreadPoolExecutor(5, 5, 1,
                TimeUnit.MINUTES, new ArrayBlockingQueue<Runnable>(20),new CustomizableThreadFactory("Tianluo-Thread-pool"));
        executorOne.execute(()->{
            throw new NullPointerException();
        });
    }
}

最佳线程数目 = （（线程等待时间+线程CPU时间）/线程CPU时间 ）* CPU数目

public class ThreadTest {
    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executorOne = new ThreadPoolExecutor(5, 5, 1,
                TimeUnit.MINUTES, new ArrayBlockingQueue<Runnable>(20),new CustomizableThreadFactory("Tianluo-Thread-pool"));
        for (int i = 0; i < 5; i++) {
            executorOne.submit(()->{
                System.out.println("current thread name" + Thread.currentThread().getName());
                Object object = null;
                System.out.print("result## " + object.toString());
            });
        }
    }
}

current thread nameTianluo-Thread-pool1
current thread nameTianluo-Thread-pool2
current thread nameTianluo-Thread-pool3
current thread nameTianluo-Thread-pool4
current thread nameTianluo-Thread-pool5

public class ThreadTest {
    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executorOne = new ThreadPoolExecutor(5, 5, 1,
                TimeUnit.MINUTES, new ArrayBlockingQueue<Runnable>(20),new CustomizableThreadFactory("Tianluo-Thread-pool"));
        for (int i = 0; i < 5; i++) {
            executorOne.submit(()->{
                System.out.println("current thread name" + Thread.currentThread().getName());
                try {
                    Object object = null;
                    System.out.print("result## " + object.toString());
                }catch (Exception e){
                    System.out.println("异常了"+e);
                }
            });
        }
    }
}

public class ThreadTest {
    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executorOne = new ThreadPoolExecutor(5, 5, 1,
                TimeUnit.MINUTES, new ArrayBlockingQueue<Runnable>(20), new CustomizableThreadFactory("Tianluo-Thread-pool"));
        executorOne.execute(() -> {
        });
        //关闭线程池
        executorOne.shutdown();
    }
}

private static final ThreadLocal<Integer> currentUser = ThreadLocal.withInitial(() -> null);
@GetMapping("wrong")
public Map wrong(@RequestParam("userId") Integer userId) {
    //设置用户信息之前先查询一次ThreadLocal中的用户信息
    String before  = Thread.currentThread().getName() + ":" + currentUser.get();
    //设置用户信息到ThreadLocal
    currentUser.set(userId);
    //设置用户信息之后再查询一次ThreadLocal中的用户信息
    String after  = Thread.currentThread().getName() + ":" + currentUser.get();
    //汇总输出两次查询结果
    Map result = new HashMap();
    result.put("before", before);
    result.put("after", after);
    return result;
}

server.tomcat.max-threads=1

@GetMapping("right")
public Map right(@RequestParam("userId") Integer userId) {
    String before  = Thread.currentThread().getName() + ":" + currentUser.get();
    currentUser.set(userId);
    try {
        String after = Thread.currentThread().getName() + ":" + currentUser.get();
        Map result = new HashMap();
        result.put("before", before);
        result.put("after", after);
        return result;
    } finally {
        //在finally代码块中删除ThreadLocal中的数据，确保数据不串
        currentUser.remove();
    }
}