创建线程池的方法_java引用就是对象本身

全栈程序员站长

发布于 2022-11-14 15:05:59

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发布于 2022-11-14 15:05:59

文章被收录于专栏：全栈程序员必看

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创建线程池的方法

一、创建线程池的三种方法

Executors.newSingleThreadExecutor(); //单个线程 Executors.newFixedThreadPool(5); //创建一个固定的线程池 Executors.newCachedThreadPool(); //创建一个可伸缩的线程池

1.newSingleThreadExecutor

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ExecuterTest1 { 

public static void main(String[] args) { 

ExecutorService threadPool = Executors.newSingleThreadExecutor();  //单个线程
try { 

for(int i=0;i<10;i++) { 

threadPool.execute(()->{ 

System.out.println(Thread.currentThread().getName()+" ok");
});
}
}catch (Exception e) { 

e.printStackTrace();
}finally { 

//关闭线程池
threadPool.shutdown();
}
}
}

2. newFixedThreadPool

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ExecuterTest1 { 

public static void main(String[] args) { 

ExecutorService threadPool = Executors.newFixedThreadPool(5); //创建一个固定的线程池
try { 

for(int i=0;i<10;i++) { 

threadPool.execute(()->{ 

System.out.println(Thread.currentThread().getName()+" ok");
});
}
}catch (Exception e) { 

e.printStackTrace();
}finally { 

//关闭线程池
threadPool.shutdown();
}
}
}

3. newCachedThreadPool

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ExecuterTest1 { 

public static void main(String[] args) { 

ExecutorService threadPool = Executors.newCachedThreadPool();  //创建一个可伸缩的线程池
try { 

for(int i=0;i<10;i++) { 

threadPool.execute(()->{ 

System.out.println(Thread.currentThread().getName()+" ok");
});
}
}catch (Exception e) { 

e.printStackTrace();
}finally { 

//关闭线程池
threadPool.shutdown();
}
}
}

二、三种方法的源码

public static ExecutorService newSingleThreadExecutor() { 

return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
//#############################################################
public static ExecutorService newFixedThreadPool(int nThreads) { 

return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
//############################################################
public static ExecutorService newCachedThreadPool() { 

return new ThreadPoolExecutor(0, Integer.MAX_VALUE,  //约等于20亿
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}

以上三种方法中都调用ThreadPoolExecutor来创建线程池。
但三种方法都存在一定的弊端：
（1）SingleThreadExecutor和FixedThreadPool允许的请求队列长度为Integer.MAX.VALUE，可能会导致OOM
（2）CachedThreadPool允许的创建线程数量为Integer.MAX.VALUE，可能会导致OOM

ThreadPoolExecutor源码分析

    public ThreadPoolExecutor(int corePoolSize,     //核心线程池大小
int maximumPoolSize,  //最大核心线程池大小
long keepAliveTime,   //超时了没有人调用就会释放
TimeUnit unit,   //超时单位
BlockingQueue<Runnable> workQueue,   //阻塞队列
ThreadFactory threadFactory,        //线程工厂，创建线程的，一般不用动
RejectedExecutionHandler handler) { 
   //拒绝策略
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}

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原始发表：2022年9月30日，如有侵权请联系 cloudcommunity@tencent.com 删除

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