标签：作用 -- cut call 异步 gate reject 很多 应用
创建使用固定线程数的FixedThreadPool，适用于为了满足资源管理的需求，而需要限制当前线程数量的应用场景，它适用于负载比较重的服务器。
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());//设定的阻塞队列是无界的
}
public static ExecutorService newWorkStealingPool(int parallelism) {
return new ForkJoinPool
(parallelism,
ForkJoinPool.defaultForkJoinWorkerThreadFactory,
null, true);
}
创建一个会根据需要创建新线程的，适用于执行很多的短期异步任务的小程序，或者是负载较轻的服务器。
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
适用于需要保证顺序地执行各个任务；并且在任意时间点，不会有多个线程是活动的应用场景。
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.acc = System.getSecurityManager() == null ?
null :
AccessController.getContext();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}
1、corePoolSize：核心线程池的大小，如果核心线程池有空闲位置，这是新的任务就会被核心线程池新建一个线程执行，执行完毕后不会销毁线程，线程会进入缓存队列等待再次被运行。
2、maximunPoolSize：线程池能创建最大的线程数量。如果核心线程池和缓存队列都已经满了，新的任务进来就会创建新的线程来执行。但是数量不能超过maximunPoolSize，否侧会采取拒绝接受任务策略，我们下面会具体分析。
3、keepAliveTime：非核心线程能够空闲的最长时间，超过时间，线程终止。这个参数默认只有在线程数量超过核心线程池大小时才会起作用。只要线程数量不超过核心线程大小，就不会起作用。
4、unit：时间单位，和keepAliveTime配合使用。
TimeUnit.DAYS; //天 TimeUnit.HOURS; //小时 TimeUnit.MINUTES; //分钟 TimeUnit.SECONDS; //秒 TimeUnit.MILLISECONDS; //毫秒 TimeUnit.MICROSECONDS; //微妙 TimeUnit.NANOSECONDS; //纳秒
5、workQueue：缓存队列，用来存放等待被执行的任务。
6、threadFactory：线程工厂，用来创建线程，一般有三种选择策略。
public class ThreadFactoryMain implements ThreadFactory{
private final String groupName;
private AtomicInteger nextId = new AtomicInteger(1);
public ThreadFactoryMain(String groupName) {
this.groupName = "ThreadFactoryMain -" + groupName + "-worker-";
}
@Override
public Thread newThread(@NotNull Runnable r) {
String threadName = groupName + nextId.incrementAndGet();
Thread thread = new Thread(null,r,threadName,0);
return thread;
}
public static void main(String[] args){
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10,50,
60L, TimeUnit.SECONDS,
new LinkedBlockingQueue<Runnable>(20),
new ThreadFactoryMain("zs.zhou"));
Stream.iterate(0,n->n+1).limit(10).forEach(i->threadPoolExecutor.submit(new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + " ::: --- " + i);
}
}));
System.out.println("end");
threadPoolExecutor.shutdown();
}
}
7、handler：拒绝处理策略，线程数量大于最大线程数就会采用拒绝处理策略，四种策略为
标签：作用 -- cut call 异步 gate reject 很多 应用
原文地址：https://www.cnblogs.com/songjn/p/13276951.html
