P5面试简要

1、共享锁、排它锁、读写锁

1. 共享锁：可以允许多个线程访问代码
2. 排它锁：只有一个线程可以访问代码
3. 读写锁：
   1. 读锁：读的时候，不允许写，但是允许同时读
   2. 写锁：写的时候，不允许写，也不允许读

2、统一锁、分段锁

1. 统一锁：大粒度的锁

•         锁定A等待B；锁定B等待A->死锁  解决方案：把A+B统一成为大锁

1. 分段锁：分成一段一段的小粒度的锁（ConcurrentHashMap)

3、间隙锁

        就是两个值之间的间隙。为了解决幻读问题，InnoDB 只好引入新的锁，也就是 间隙锁 (Gap Lock)。幻读仅专指“新插入的行”。

4、行锁

        给某一行加的锁

5、线程池的7个参数

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

static class DefaultThreadFactory implements ThreadFactory {
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private final String namePrefix;

        DefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r,
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

/**
     * Thread factory capturing access control context and class loader
     */
    static class PrivilegedThreadFactory extends DefaultThreadFactory {
        private final AccessControlContext acc;
        private final ClassLoader ccl;

        PrivilegedThreadFactory() {
            super();
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                // Calls to getContextClassLoader from this class
                // never trigger a security check, but we check
                // whether our callers have this permission anyways.
                sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

                // Fail fast
                sm.checkPermission(new RuntimePermission("setContextClassLoader"));
            }
            this.acc = AccessController.getContext();
            this.ccl = Thread.currentThread().getContextClassLoader();
        }

        public Thread newThread(final Runnable r) {
            return super.newThread(new Runnable() {
                public void run() {
                    AccessController.doPrivileged(new PrivilegedAction<Void>() {
                        public Void run() {
                            Thread.currentThread().setContextClassLoader(ccl);
                            r.run();
                            return null;
                        }
                    }, acc);
                }
            });
        }
    }

package com.itheima.security.springboot.test;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 自己的线程工具类
 *
 * @Auther: Vector
 * @Date: ${DATE} * @Description: ${PACKAGE_NAME} * @version: 1.0
 */
public class ThreadPoolUtil {
    /**
     * 核心线程数
     */
    private static final int SIZE_CORE_POOL = 5;
    /**
     * 最大线程数
     */
    private static final int SIZE_MAX_POOL = 10;
    /**
     * 存活时间
     */
    private static final long ALIVE_TIME = 2000;

    /**
     * 存放任务的队列
     */
    private static BlockingQueue<Runnable> bqueue = new ArrayBlockingQueue<>(60);

    /**
     * The default rejected execution handler
     */
    private static final RejectedExecutionHandler defaultHandler =
            new ThreadPoolExecutor.AbortPolicy();

    private static ThreadPoolExecutor pool = new ThreadPoolExecutor(SIZE_CORE_POOL, SIZE_MAX_POOL, ALIVE_TIME, TimeUnit.MILLISECONDS, bqueue, ThreadPoolUtil.myDefaultThreadFactory(), defaultHandler);

    static {
        pool.prestartAllCoreThreads();
    }

    public static ThreadPoolExecutor getPool() {

        return pool;
    }

    public static ThreadFactory myDefaultThreadFactory() {
        return new MyDefaultThreadFactory();
    }

    static class MyDefaultThreadFactory implements ThreadFactory {
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private final String namePrefix;

        MyDefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() :
                    Thread.currentThread().getThreadGroup();
            namePrefix = "dcss-account" +
                    poolNumber.getAndIncrement() +
                    "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r,
                    namePrefix + threadNumber.getAndIncrement(),
                    0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

}