java Semaphore信号亮-同意多个任务同一时候訪问这个资源--thinking in java21.7.6
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package org.rui.thread.newc.semaphore;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Semaphore;
/**
* 同意N个任务同一时候訪问这个资源
* @author lenovo
*
* @param <T>
*/
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;
checkedOut = new boolean[size];
available = new Semaphore(size, true);
// load pool with objects that can be checked out:能够检查的对象的负载池
for (int i = 0; i < size; i++)
{
// assumes a default constructor自己的默认构造函数
try
{
// Object o=classObject.newInstance();
// Fat f=(Fat) classObject.newInstance();
items.add(classObject.newInstance());
} catch (Exception e)
{
throw new RuntimeException(e);
}
}
}
//假设你须要一个新对象，那么你能够调用checkOut(),在使用完后递交给checkIn()
public T checkOut() throws InterruptedException
{
//假设没有不论什么的Semaphore许何证，意味着池中没有对象可用了
available.acquire();//获取一个许可（假设提供了一个）并马上返回，将可用的许可数减 1。
return getItems();
}
public void checkIn(T x)
{
if (releaseItem(x))
//假设被签入的对象有效，则会向信号亮返回一个许可证
available.release();//释放一个许可，将其返回给信号量。
}
private synchronized T getItems()
{
for (int i = 0; i < size; ++i)
{
//System.out.println(checkedOut[i]);
if (!checkedOut[i])//假设为false 说明是releaseItem 则能够签出
{
checkedOut[i] = true;
//System.out.println("xxxxxx===="+items.get(i));
return items.get(i);
}
}
return null;// semaphore prevents reaching here防止信号到达这里
}
private synchronized boolean releaseItem(T item)
{
int index = items.indexOf(item);
if (index == -1)
return false;// not in the list
if (checkedOut[index])//假设为true 则说明已签出 则能够释放
{
//System.out.println("releaseItem:"+item);
checkedOut[index] = false;
return true;
}
return false;// wasn‘t checked out 没有签出
}
}
package org.rui.thread.newc.semaphore;
public class Fat
{
private volatile double d;
private static int counter = 0;
private final int id = counter++;
public Fat()
{
// expensive, interruptible operation:
for (int i = 1; i < 10000; i++)
{
d += (Math.PI + Math.E) / (double) i;
}
}
public void operation()
{
System.out.println("operation>> "+this);
}
@Override
public String toString()
{
return "Fat>>id:" + id;
}
}
<pre name="code" class="java">package org.rui.thread.newc.semaphore;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
class CheckoutTask<T> implements Runnable
{
private static int counter = 0;
private final int id = counter++;
private int index;
private Pool<T> pool;
public CheckoutTask(Pool<T> pool, int size)
{
this.pool = pool;
this.index = size;
}
@Override
public void run()
{
try
{
T item = pool.checkOut();
System.out.println(this + "checked out 已签出:" + item);
TimeUnit.SECONDS.sleep(1);
System.out.println("checked in 释放:" + item);
pool.checkIn(item);// 将用完的对像释放
// System.out.println(index+" counter="+counter+" id=="+id);
// if(index==counter-1){
// TimeUnit.SECONDS.sleep(1);
// System.out.println("=======all checkoutTasks created");
//
// }
} catch (InterruptedException e)
{
System.out.println(e.getMessage());
// TODO Auto-generated catch block
// e.printStackTrace();
}
}
@Override
public String toString()
{
return "checkoutTask " + id + " ";
}
}
// //////////////////////////
public class SemaphoreDemo
{
final static int Size = 25;
public static void main(String[] args) throws InterruptedException
{
final Pool<Fat> pool = new Pool<Fat>(Fat.class, Size);
ExecutorService exec = Executors.newCachedThreadPool();
// 開始操练pool
for (int i = 0; i < Size; i++)
{
exec.execute(new CheckoutTask<Fat>(pool, i));
}
System.out.println("all checkoutTasks created");
// main 開始签出pool中的Fat对象 -1,但并不签入他们。
// 一但池中的全部的对象都被签出后，semaphore将不在运行不论什么签出操作，
List<Fat> list = new ArrayList<Fat>();
for (int i = 0; i < Size; i++)
{
try
{
Fat f = pool.checkOut();
System.out.println(i + " >>main() thrad checked out 签出");
f.operation();
list.add(f);
} catch (InterruptedException e)
{
e.printStackTrace();
}
}
// 无对象可签出 run 会堵塞
Future<?
> blocked = exec.submit(new Runnable()
{
@Override
public void run()
{
try
{
// semaphore prevents additional checkout 信号量防止额外的校验
// so call is blocked 因此调用被堵塞
pool.checkOut();
} catch (InterruptedException e)
{
System.err.print("checkOut() interrupted");
// e.printStackTrace();
}
}
});
// 持有一段时间后再将它们签入
TimeUnit.SECONDS.sleep(2);
// 以此来挣脱future。取消,冗余的签入将被pool忽略
System.out.println("任务是否完毕："+blocked.isDone());
blocked.cancel(true);// break out of blocked call 中断呼叫中断 试图取消对此任务的运行
System.out.println();
/////////////////都签入之后 再能够继续使用pool
for (Fat f : list)
{
pool.checkIn(f);
}
//这里事实上能够再次使用pool了，
for (Fat f : list)
{
pool.checkIn(f);// second checkin ignored 二签忽略
}
// exec.shutdown();
}
}
/**
* output:
* checkoutTask 0 checked out 已签出:Fat>>id:0
checkoutTask 2 checked out 已签出:Fat>>id:2
checkoutTask 1 checked out 已签出:Fat>>id:1
checkoutTask 4 checked out 已签出:Fat>>id:3
checkoutTask 3 checked out 已签出:Fat>>id:4
checkoutTask 5 checked out 已签出:Fat>>id:5
checkoutTask 6 checked out 已签出:Fat>>id:6
checkoutTask 7 checked out 已签出:Fat>>id:7
checkoutTask 8 checked out 已签出:Fat>>id:8
checkoutTask 9 checked out 已签出:Fat>>id:9
checkoutTask 10 checked out 已签出:Fat>>id:10
checkoutTask 11 checked out 已签出:Fat>>id:11
checkoutTask 12 checked out 已签出:Fat>>id:12
checkoutTask 13 checked out 已签出:Fat>>id:13
checkoutTask 14 checked out 已签出:Fat>>id:14
checkoutTask 15 checked out 已签出:Fat>>id:15
checkoutTask 16 checked out 已签出:Fat>>id:16
checkoutTask 18 checked out 已签出:Fat>>id:18
checkoutTask 17 checked out 已签出:Fat>>id:17
checkoutTask 19 checked out 已签出:Fat>>id:19
checkoutTask 20 checked out 已签出:Fat>>id:20
checkoutTask 21 checked out 已签出:Fat>>id:21
checkoutTask 22 checked out 已签出:Fat>>id:22
checkoutTask 23 checked out 已签出:Fat>>id:23
all checkoutTasks created
0 >>main() thrad checked out 签出
operation>> Fat>>id:24
checked in 释放:Fat>>id:1
checkoutTask 24 checked out 已签出:Fat>>id:1
checked in 释放:Fat>>id:2
1 >>main() thrad checked out 签出
operation>> Fat>>id:2
checked in 释放:Fat>>id:0
2 >>main() thrad checked out 签出
operation>> Fat>>id:0
checked in 释放:Fat>>id:3
3 >>main() thrad checked out 签出
operation>> Fat>>id:3
checked in 释放:Fat>>id:4
4 >>main() thrad checked out 签出
operation>> Fat>>id:4
checked in 释放:Fat>>id:5
5 >>main() thrad checked out 签出
operation>> Fat>>id:5
checked in 释放:Fat>>id:7
6 >>main() thrad checked out 签出
operation>> Fat>>id:7
checked in 释放:Fat>>id:9
7 >>main() thrad checked out 签出
operation>> Fat>>id:9
checked in 释放:Fat>>id:11
8 >>main() thrad checked out 签出
operation>> Fat>>id:11
checked in 释放:Fat>>id:13
9 >>main() thrad checked out 签出
operation>> Fat>>id:13
checked in 释放:Fat>>id:15
10 >>main() thrad checked out 签出
operation>> Fat>>id:15
checked in 释放:Fat>>id:17
11 >>main() thrad checked out 签出
operation>> Fat>>id:17
checked in 释放:Fat>>id:21
12 >>main() thrad checked out 签出
operation>> Fat>>id:21
checked in 释放:Fat>>id:19
13 >>main() thrad checked out 签出
operation>> Fat>>id:19
checked in 释放:Fat>>id:23
14 >>main() thrad checked out 签出
operation>> Fat>>id:23
checked in 释放:Fat>>id:8
checked in 释放:Fat>>id:6
15 >>main() thrad checked out 签出
operation>> Fat>>id:6
16 >>main() thrad checked out 签出
operation>> Fat>>id:8
checked in 释放:Fat>>id:10
17 >>main() thrad checked out 签出
checked in 释放:Fat>>id:14
checked in 释放:Fat>>id:16
checked in 释放:Fat>>id:18
checked in 释放:Fat>>id:20
checked in 释放:Fat>>id:22
checked in 释放:Fat>>id:12
operation>> Fat>>id:10
18 >>main() thrad checked out 签出
operation>> Fat>>id:12
19 >>main() thrad checked out 签出
operation>> Fat>>id:14
20 >>main() thrad checked out 签出
operation>> Fat>>id:16
21 >>main() thrad checked out 签出
operation>> Fat>>id:18
22 >>main() thrad checked out 签出
operation>> Fat>>id:20
23 >>main() thrad checked out 签出
operation>> Fat>>id:22
checked in 释放:Fat>>id:1
24 >>main() thrad checked out 签出
operation>> Fat>>id:1
任务是否完毕：false
checkOut() interrupted
*/
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