Leetcode_1115_交替打印FoodBar_多线程

法1：volatile

class FooBar {
    private int n;

    volatile private boolean flag = false;

    public FooBar(int n) {
        this.n = n;
    }

    public void foo(Runnable printFoo) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            while(flag == true){
                Thread.yield();
            }
        	// printFoo.run() outputs "foo". Do not change or remove this line.
        	printFoo.run();
            flag = true;
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        
        for (int i = 0; i < n; i++) {
            while(flag == false){
                Thread.yield();
            }
            // printBar.run() outputs "bar". Do not change or remove this line.
        	printBar.run();
            flag = false;
        }
    }
}

法2：原子

import java.util.concurrent.atomic.AtomicBoolean;
class FooBar {
    private int n;

    AtomicBoolean flag = new AtomicBoolean(false);

    public FooBar(int n) {
        this.n = n;
    }

    public void foo(Runnable printFoo) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            while(flag.get() == true){
                Thread.yield();
            }
        	// printFoo.run() outputs "foo". Do not change or remove this line.
        	printFoo.run();
            flag.set(true);
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        
        for (int i = 0; i < n; i++) {
            while(flag.get() == false){
                Thread.yield();
            }
            // printBar.run() outputs "bar". Do not change or remove this line.
        	printBar.run();
            flag.set(false);
        }
    }
}

法3：信号量

import java.util.concurrent.Semaphore;
class FooBar {
    private int n;
    private final Semaphore sfoo = new Semaphore(1);
    private final Semaphore sbar = new Semaphore(0);
    public FooBar(int n) {
        this.n = n;
    }

    public void foo(Runnable printFoo) throws InterruptedException {
        
        for (int i = 0; i < n; i++) {
            sfoo.acquire();
        	// printFoo.run() outputs "foo". Do not change or remove this line.
        	printFoo.run();
            sbar.release();
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        
        for (int i = 0; i < n; i++) {
            sbar.acquire();
            // printBar.run() outputs "bar". Do not change or remove this line.
        	printBar.run();
            sfoo.release();
        }
    }
}