作者：折纸
集体博客：https://www.zhezhi.press
记录菜鸡的成长之旅！
题目形容
咱们提供了一个类：
public class Foo {
public void first() { print("first"); }
public void second() { print("second"); }
public void third() { print("third"); }
}三个不同的线程 A、B、C 将会共用一个Foo实例。
- 一个将会调用
first()办法 - 一个将会调用
second()办法 - 还有一个将会调用
third()办法
请设计批改程序，以确保second()办法在first()办法之后被执行，third()办法在second()办法之后被执行。
示例 1:
输出: [1,2,3]
输入: “firstsecondthird”
解释:
有三个线程会被异步启动。
输出 [1,2,3] 示意线程 A 将会调用 first() 办法，线程 B 将会调用 second() 办法，线程 C 将会调用 third() 办法。
正确的输入是 “firstsecondthird”。
示例 2:
输出: [1,3,2]
输入: “firstsecondthird”
解释:
输出 [1,3,2] 示意线程 A 将会调用 first() 办法，线程 B 将会调用 third() 办法，线程 C 将会调用 second() 办法。
正确的输入是 “firstsecondthird”。
提醒：
- 只管输出中的数字仿佛暗示了程序，然而咱们并不保障线程在操作系统中的调度程序。
- 你看到的输出格局次要是为了确保测试的全面性。
话不多说 间接上代码，简略温习一下Lock、synchronized、还有CountDownLatch、Semaphore、CyclicBarrier等工具类的应用
ReentrantLock + Condition
class Foo {
ReentrantLock lock = new ReentrantLock();
Condition a = lock.newCondition();
Condition b = lock.newCondition();
Condition c = lock.newCondition();
private volatile int status = 1;
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
try{
lock.lock();
while(status!=1){
a.await();
}
status = 2;
printFirst.run();
b.signal();
}finally{
lock.unlock();
}
// printFirst.run() outputs "first". Do not change or remove this line.
}
public void second(Runnable printSecond) throws InterruptedException {
try{
lock.lock();
while(status!=2){
b.await();
}
status = 3;
printSecond.run();
c.signal();
}finally{
lock.unlock();
}
// printSecond.run() outputs "second". Do not change or remove this line.
}
public void third(Runnable printThird) throws InterruptedException {
try{
lock.lock();
while(status!=3){
c.await();
}
status = 1;
printThird.run();
a.signal();
}finally{
lock.unlock();
}
// printThird.run() outputs "third". Do not change or remove this line.
}
}LockSupport
class Foo {
static Thread aThread = null,bThread = null,cThread = null;
private volatile int status = 1;
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
aThread = Thread.currentThread();
printFirst.run();
status = 2;
LockSupport.unpark(bThread);
// printFirst.run() outputs "first". Do not change or remove this line.
// printFirst.run();
}
public void second(Runnable printSecond) throws InterruptedException {
bThread = Thread.currentThread();
while(status!=2)
LockSupport.park();
printSecond.run();
status = 3;
LockSupport.unpark(cThread);
// printSecond.run() outputs "second". Do not change or remove this line.
// printSecond.run();
}
public void third(Runnable printThird) throws InterruptedException {
cThread = Thread.currentThread();
while(status!=3)
LockSupport.park();
printThird.run();
status = 1;
LockSupport.unpark(aThread);
// printThird.run() outputs "third". Do not change or remove this line.
// printThird.run();
}
}synchronized + wait/notify
class Foo {
Object lock = new Object();
private volatile int status = 1;
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
synchronized(lock){
while(status!=1){
lock.wait();
}
printFirst.run();
status = 2;
lock.notifyAll();
}
// printFirst.run() outputs "first". Do not change or remove this line.
}
public void second(Runnable printSecond) throws InterruptedException {
synchronized(lock){
while(status!=2){
lock.wait();
}
printSecond.run();
status = 3;
lock.notifyAll();
}
// printSecond.run() outputs "second". Do not change or remove this line.
}
public void third(Runnable printThird) throws InterruptedException {
synchronized(lock){
while(status!=3){
lock.wait();
}
printThird.run();
status = 1;
lock.notifyAll();
}
// printThird.run() outputs "third". Do not change or remove this line.
}
}Semaphore
class Foo {
Semaphore s = new Semaphore(1);
private volatile int status = 1;
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
while(status!=1){
}
s.acquire();
// printFirst.run() outputs "first". Do not change or remove this line.
printFirst.run();
status = 2;
s.release();
}
public void second(Runnable printSecond) throws InterruptedException {
while(status!=2){
}
s.acquire();
// printFirst.run() outputs "first". Do not change or remove this line.
printSecond.run();
status = 3;
s.release();
// printSecond.run() outputs "second". Do not change or remove this line.
}
public void third(Runnable printThird) throws InterruptedException {
while(status!=3){
}
s.acquire();
// printFirst.run() outputs "first". Do not change or remove this line.
printThird.run();
status = 1;
s.release();
// printThird.run() outputs "third". Do not change or remove this line.
}
}CountDownLatch
class Foo {
CountDownLatch aLatch = new CountDownLatch(1);
CountDownLatch bLatch = new CountDownLatch(1);
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
// printFirst.run() outputs "first". Do not change or remove this line.
printFirst.run();
aLatch.countDown();
}
public void second(Runnable printSecond) throws InterruptedException {
aLatch.await();//aLatch计数器为1，当线程1打印结束后--为0，这里不再被阻塞 线程2开始打印
// printSecond.run() outputs "second". Do not change or remove this line.
printSecond.run();
bLatch.countDown();
}
public void third(Runnable printThird) throws InterruptedException {
bLatch.await();//bLatch计数器为1，当线程1打印结束后--为0，这里不再被阻塞 线程2开始打印
// printThird.run() outputs "third". Do not change or remove this line.
printThird.run();
}
}CyclicBarrier
class Foo {
CyclicBarrier cy1 = new CyclicBarrier(2);
CyclicBarrier cy2 = new CyclicBarrier(2);
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
// printFirst.run() outputs "first". Do not change or remove this line.
printFirst.run();
try{
cy1.await();
}catch(BrokenBarrierException e){
e.printStackTrace();
}
}
public void second(Runnable printSecond) throws InterruptedException {
try{
cy1.await(); //线程1曾经通过了cy1示意线程1曾经打印结束
//当线程1 和2都达到此处后 线程2才开始打印
printSecond.run();
cy2.await();//线程2达到屏障2
}catch(BrokenBarrierException e){
e.printStackTrace();
}
// printSecond.run() outputs "second". Do not change or remove this line.
}
public void third(Runnable printThird) throws InterruptedException {
try{
cy2.await();//线程2打印结束后线程3才开始打印
printThird.run();
}catch(BrokenBarrierException e){
e.printStackTrace();
}
// printThird.run() outputs "third". Do not change or remove this line.
}
}
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