Java并发编程基础

线程的状态

名称	说明
NEW	初始状态，线程被构建，但还没有调用start()方法
RUNNABLE	运行状态，java线程将操作系统中的就绪和运行统称为运行中
BLOCKED	阻塞状态，表示线程阻塞于锁
WAITING	等待状态，当前线程需要等待其他线程做出一些特定动作（通知或中断）
TIME_WAITING	超时等待状态，不同于WAITING，它可以在指定的时间自行返回的
TERMINATED	终止状态

Daemon线程

线程默认不是daemon线程，需要setDaemon(true)。daemon线程的finally方法，不一定有机会执行。

启动和终止

suspend()、resume()和stop()

suspend方法在调用后，线程不会释放已经占有的资源，而是占用资源进入睡眠状态。
同样，stop方法在中介一个线程时不会保证线程的资源正常释放，通常是没有给予线程完成资源释放工作的机会。

进程间通信

volatile和synchronized的方式

通过共享变量的方式

等待/通知机制

wait/notify(notifyAll)

指线程A调用了对象O的wait方法进入等待状态，而线程B通过调用对象O的notify或者notifyAll方法来唤醒A线程，A线程从wait方法返回继续执行。

1. 调用waie、notify、notifyAll方法时，需要先对调用对象加锁
2. 调用wait后，释放锁。线程状态由running变为waiting
3. notify、notifyAll释放所之后，wait的线程才能获取锁。
4. 调用notify、notifyAll后，等待线程从等待队列中移到同步队列中，被移动的线程的状态由WATING变为BLOCKED

使用方式：

1. Thread.join
2. 线程池
3. 数据库连接池

LockSupport

1. Condition(await、signal、signalAll)
2. AbstractQueuedSynchronizer
   1. ReentrantLock
   2. CountDownLatch
   3. …

ThreadLocal

线程应用实例

等待超时模式

long future = System.currentTimeMillis() + mills;
long remaining = mills;
while(remaining > 0){
    wait(remaing);
    remaining = future - System.currentTimeMillis();
}

线程池

package com.iforfee.common.thread;


import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;

/**
 * @author joyo
 * @date 2018/3/14
 */
public class DefaultThreadPool<Job extends Runnable> implements ThreadPool<Job> {

    private static final int MAX_WORKER_NUMBERS = 10;
    private static final int DEFAULT_WORKER_NUMBERS = 5;
    private static final int MIN_WORKER_NUMBERS = 1;

    private final LinkedList<Job> jobs = new LinkedList<Job>();
    private final List<Worker> workers = Collections.synchronizedList(new ArrayList<Worker>());

    private int workerNum = DEFAULT_WORKER_NUMBERS;
    private AtomicLong threadNum = new AtomicLong();

    public DefaultThreadPool() {
        initializeWokers(DEFAULT_WORKER_NUMBERS);
    }

    public DefaultThreadPool(int num) {
        workerNum = num > MAX_WORKER_NUMBERS ? MAX_WORKER_NUMBERS : num < MIN_WORKER_NUMBERS ? MIN_WORKER_NUMBERS : num;
        initializeWokers(workerNum);
    }

    @Override
    public void execute(Job job) {
        if (job != null) {
            synchronized (jobs) {
                jobs.addLast(job);
                jobs.notify();
            }
        }
    }

    @Override
    public void shutdown() {
        workers.forEach(job -> job.shutdown());
    }

    @Override
    public void addWorkers(int num) {
        synchronized (jobs) {
            if (num + this.workerNum > MAX_WORKER_NUMBERS) {
                num = MAX_WORKER_NUMBERS - this.workerNum;
            }
            initializeWokers(num);
            this.workerNum += num;
        }
    }

    @Override
    public void removeWorker(int num) {
        synchronized (jobs) {
            if (num >= this.workerNum) {
                throw new IllegalArgumentException("beyond workerNum");
            }

            int count = 0;
            while (count < num) {
                Worker worker = workers.get(count);
                if (workers.remove(worker)) {
                    worker.shutdown();
                    count++;
                }
                this.workerNum -= count;
            }
        }
    }

    @Override
    public int getJobSize() {
        return jobs.size();
    }

    private void initializeWokers(int num) {
        for (int i = 0; i < num; i++) {
            Worker worker = new Worker();
            workers.add(worker);
            Thread thread = new Thread(worker, "ThreadPool-Worker-" + threadNum.incrementAndGet());
            thread.start();
        }
    }


    class Worker implements Runnable {

        private volatile boolean running = true;

        @Override
        public void run() {
            while (running) {
                Job job = null;
                synchronized (jobs) {
                    while (jobs.isEmpty()) {
                        try {
                            jobs.wait();
                        } catch (InterruptedException e) {
                            Thread.currentThread().interrupt();
                            return;
                        }
                    }
                    job = jobs.removeFirst();
                }
                if (job != null) {
                    try {
                        job.run();
                    } catch (Exception ex) {
                        //ignore exception from job
                    }
                }
            }
        }

        public void shutdown() {
            running = false;
        }
    }

}

interface ThreadPool<Job extends Runnable> {
    void execute(Job job);

    void shutdown();

    void addWorkers(int num);

    void removeWorker(int num);

    int getJobSize();
}

数据库连接池

web服务器