模式1--SingleThreadExecution

来至《java多线程设计模式》

一、方法：用synchronized方法，每次只让一个通过。

public class UserThread extends Thread {
    private final Gate gate;
    private final String myname;
    private final String myaddress;
    public UserThread(Gate gate, String myname, String myaddress) {
        this.gate = gate;
        this.myname = myname;
        this.myaddress = myaddress;
    }
    public void run() {
        System.out.println(myname + " BEGIN");
        while (true) {
            gate.pass(myname, myaddress);
        }
    }
}

public class Gate {
    private int counter = 0;
    private String name = "Nobody";
    private String address = "Nowhere";
    public void pass(String name, String address) {
        this.counter++;
        this.name = name;
        this.address = address;
        check();
    }
    public String toString() {
        return "No." + counter + ": " + name + ", " + address;
    }
    private void check() {
        if (name.charAt(0) != address.charAt(0)) {
            System.out.println("***** BROKEN ***** " + toString());
        }
    }
}

每次只让一个通过：

public class Gate {
    private int counter = 0;
    private String name = "Nobody";
    private String address = "Nowhere";
    public synchronized void pass(String name, String address) {
        this.counter++;
        this.name = name;
        this.address = address;
        check();
    }
    public synchronized String toString() {
        return "No." + counter + ": " + name + ", " + address;
    }
    private void check() {
        if (name.charAt(0) != address.charAt(0)) {
            System.out.println("***** BROKEN ***** " + toString());
        }
    }
}

二、让错误更容易发生：在延迟占用临界区的时间：

public class Gate {
    private int counter = 0;
    private String name = "Nobody";
    private String address = "Nowhere";
    public void pass(String name, String address) {
        this.counter++;
        this.name = name;
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
        }
        this.address = address;
        check();
    }
    public String toString() {
        return "No." + counter + ": " + name + ", " + address;
    }
    private void check() {
        if (name.charAt(0) != address.charAt(0)) {
            System.out.println("***** BROKEN ***** " + toString());
        }
    }
}

三、避免死锁：

  （1）多个共享资源

  （2）未释放锁定就去试图锁定另外一个

  （3）获取A--》获取B，或获取B--》获取A，A/B的获取顺序对等，没有优先级

  只要破坏以上一个即可避免死锁：

public class Main {
    public static void main(String[] args) {
        System.out.println("Testing EaterThread, hit CTRL+C to exit.");
        Tool spoon = new Tool("Spoon");
        Tool fork = new Tool("Fork");
        new EaterThread("Alice", spoon, fork).start();
        new EaterThread("Bobby", fork, spoon).start();
    }
}

破坏（3）：

public class Main {
    public static void main(String[] args) {
        System.out.println("Testing EaterThread, hit CTRL+C to exit.");
        Tool spoon = new Tool("Spoon");
        Tool fork = new Tool("Fork");
        new EaterThread("Alice", spoon, fork).start();
        new EaterThread("Bobby", spoon, fork).start();
    }
}

都先去获取spoon再去获取fork。

 

破坏（1）：

修改为一个共享资源：

public class Main {
    public static void main(String[] args) {
        System.out.println("Testing EaterThread, hit CTRL+C to exit.");
        Tool spoon = new Tool("Spoon");
        Tool fork = new Tool("Fork");
        Pair pair = new Pair(spoon, fork);
        new EaterThread("Alice", pair).start();
        new EaterThread("Bobby", pair).start();
    }
}

 public void eat() {
        synchronized (pair) {
            System.out.println(name + " takes up " + pair + ".");
            System.out.println(name + " is eating now, yam yam!");
            System.out.println(name + " puts down " + pair + ".");
        }
    }