class ZeroEvenOdd {
public ZeroEvenOdd(int n) { ... } // 构造函数
public void zero(printNumber) { ... } // 仅打印出 0
public void even(printNumber) { ... } // 仅打印出 偶数
public void odd(printNumber) { ... } // 仅打印出 奇数
}
相同的一个 ZeroEvenOdd 类实例将会传递给三个不同的线程：
线程 A 将调用 zero()，它只输出 0 。
线程 B 将调用 even()，它只输出偶数。
线程 C 将调用 odd()，它只输出奇数。
每个线程都有一个 printNumber 方法来输出一个整数。请修改给出的代码以输出整数序列 010203040506... ，其中序列的长度必须为 2n。
示例 1：
输入：n = 2
输出："0102"
说明：三条线程异步执行，其中一个调用 zero()，另一个线程调用 even()，最后一个线程调用odd()。正确的输出为 "0102"。
示例 2：
输入：n = 5
输出："0102030405"
写法1：使用volatile的可见性，让变量来控制，Thread.yield()使线程让出当前时间片给其他线程执行。
public class ZeroEvenOdd {
//定义flag，为0代表执行zero，为1代表执行odd（奇数），为2代表执行even（偶数）
private volatile int flag = 0;
private int n;
public ZeroEvenOdd(int n) {
this.n = n;
}
// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 0; i < n; i++) {
while (flag != 0){
Thread.yield();
}
printNumber.accept(0);
if (i % 2 != 0){
flag = 2;
}else {
flag = 1;
}
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 2; i <= n; i=i+2) {
while (flag != 2){
Thread.yield();
}
printNumber.accept(i);
flag = 0;
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i=i+2) {
while (flag != 1){
Thread.yield();
}
printNumber.accept(i);
flag = 0;
}
}
}
写法2：使用信号量Semaphore，先获取许可证，再执行。
public class ZeroEvenOdd {
private Semaphore z = new Semaphore(1);
private Semaphore e = new Semaphore(0);
private Semaphore o = new Semaphore(0);
private int n;
public ZeroEvenOdd(int n) {
this.n = n;
}
// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
for(int i = 0; i < n; i++){
z.acquire();
printNumber.accept(0);
if(i % 2 == 0){
o.release();
} else {
e.release();
}
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for(int i = 2; i <= n; i+=2){
e.acquire();
printNumber.accept(i);
z.release();
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for(int i = 1; i <= n; i+=2){
o.acquire();
printNumber.accept(i);
z.release();
}
}
}
写法3：加锁
public class ZeroEvenOdd {
private volatile int flag = 0;
private Lock lock = new ReentrantLock();
private Condition z = lock.newCondition();
private Condition e = lock.newCondition();
private Condition o = lock.newCondition();
private int n;
public ZeroEvenOdd(int n) {
this.n = n;
}
// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
lock.lock();
try{
for(int i = 0; i < n; i++){
while(flag != 0){
z.await();
}
printNumber.accept(0);
if(i % 2 == 0){
flag = 1;
o.signal();
} else {
flag = 2;
e.signal();
}
z.await();
}
} finally{
lock.unlock();
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
lock.lock();
try{
for(int i = 2; i <= n; i+=2){
while(flag != 2){
e.await();
}
printNumber.accept(i);
flag = 0;
z.signal();
}
}
finally{
lock.unlock();
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
lock.lock();
try{
for(int i = 1; i <= n; i+=2){
while(flag != 1){
o.await();
};
printNumber.accept(i);
flag = 0;
z.signal();
}
} finally{
lock.unlock();
}
}
}
