线程池
线程池:三大方法,七大参数,四种拒绝策略
池化技术:事先准备好一些资源,有人要用,就来这里拿,用完之后还给。
程序的运行,本质:占用系统的资源!优化资源的使用!=>池化技术
线程池的好处
1、降低资源的消耗
2、提高响应的速度
3、方便管理
线程复用,可以控制最大并发数,管理线程
线程三大方法
package com.bjw.pool;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
// Executors
public class Demo01 {
public static void main(String[] args) {
//ExecutorService threadPool = Executors.newSingleThreadExecutor(); //单个线程
//ExecutorService threadPool2 = Executors.newFixedThreadPool(5); //创建一个固定的线程池的大小
ExecutorService threadPool3 = Executors.newCachedThreadPool(); //可伸缩的,遇强则强,遇弱则弱
try {
for (int i = 0; i < 100; i++) {
//使用了线程池之后,使用线程池来创建线程
threadPool3.execute(()->{
System.out.println(Thread.currentThread().getName()+"ok");
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 线程池用完,程序结束,关闭线程池
threadPool3.shutdown();
}
}
}
七大参数
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,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
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;
}
四种拒绝策略
package com.bjw.pool;
import java.util.concurrent.*;
// Executors
/*
* ThreadPoolExecutor.AbortPolicy():RejectedExecutionException 银行满了,还有人进来,不处理这个人,抛出异常
* ThreadPoolExecutor.CallerRunsPolicy();//哪来的去哪里
* ThreadPoolExecutor.DiscardPolicy();//队列满了,丢掉任务,不抛出异常
* ThreadPoolExecutor.DiscardOldestPolicy();//队列满了,尝试和最早的竞争,也不会抛出异常
* */
public class Demo01 {
public static void main(String[] args) {
/*ExecutorService threadPool = Executors.newSingleThreadExecutor(); //单个线程
ExecutorService threadPool2 = Executors.newFixedThreadPool(5); //创建一个固定的线程池的大小
ExecutorService threadPool3 = Executors.newCachedThreadPool(); //可伸缩的,遇强则强,遇弱则弱*/
ExecutorService threadPool = new ThreadPoolExecutor(
2,
5,
3,
TimeUnit.SECONDS,
new LinkedBlockingDeque<>(3),
Executors.defaultThreadFactory(),
new ThreadPoolExecutor.DiscardPolicy()
);
try {
//最大承载:Deque + max
for (int i = 1; i <= 9; i++) {
//使用了线程池之后,使用线程池来创建线程
threadPool.execute(()->{
System.out.println(Thread.currentThread().getName()+"ok");
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 线程池用完,程序结束,关闭线程池
threadPool.shutdown();
}
}
}
小结
了解:IO密集型,CPU密集型(调优)
/*
* 最大线程应该如何定义
* 1、CPU密集型,几核就是几,可以保证cpu的效率最高
* 2、IO密集型,判断程序中十分耗IO的线程
* */
//获取cup的核数
System.out.println(Runtime.getRuntime().availableProcessors());