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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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