package Chapter21.Concurrency;

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.Semaphore;

public class Pool<T>{

private int size;

private List<T> items = new ArrayList<T>();

private volatile boolean[] checkedOut;

private Semaphore available;

public Pool(Class<T> classObject,int size) {

this.size = size;

//初始为false

checkedOut = new boolean[size];

available = new Semaphore(size,true);

for(int i=0;i<size;i++) {

try {

items.add(classObject.newInstance());

}catch(Exception e) {

throw new RuntimeException();

}

}

}

public T checkOut() throws InterruptedException {

available.acquire();

return getItem();

}

public void checkIn(T x) {

if(releaseItem(x)) {

available.release();

}

}

//获取池中为false的对象

private synchronized T getItem() {

for(int i=0;i<size;i++) {

if(!checkedOut[i]) {

checkedOut[i] = true;

return items.get(i);

}

}

return null;

}

private synchronized boolean releaseItem(T item) {

int index = items.indexOf(item);

if(index == -1) {

return false;

}

//true的说明是已经被用的

if(checkedOut[index]) {

checkedOut[index] = false;

return true;

}

return false;

}

}