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Three ways to create thread pool source code
In fact, the thread pool is created by creating ThreadPoolExecutor
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, //21亿，导致OOM
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
Create ThreadPoolExecutor source code
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.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;
}
Manually create a thread pool
java code
package com.add;
import java.util.concurrent.*;
/**
* Created by zjl
* 2020/11/25
**/
/*** new ThreadPoolExecutor.AbortPolicy() // 银行满了，还有人进来，不处理这个人的，抛出异 常
* * new ThreadPoolExecutor.CallerRunsPolicy() // 哪来的去哪里！
* * new ThreadPoolExecutor.DiscardPolicy() //队列满了，丢掉任务，不会抛出异常！
* * new ThreadPoolExecutor.DiscardOldestPolicy() //队列满了，尝试去和最早的竞争，也不会 抛出异常！
* */
public class ExecutorsTest2 {
public static void main(String[] args) {
//自定义线程池
ExecutorService threadPool = new ThreadPoolExecutor(
2, //核心线程数
7, //核心最大线程数
1, //超时时间 1s，超过1秒没人使用，会断开线程
TimeUnit.SECONDS, //超时单位 s
new LinkedBlockingDeque<>(3), //阻塞队列 大小设置3
Executors.defaultThreadFactory(), // 线程工厂：创建线程的，一般不用动
new ThreadPoolExecutor.AbortPolicy() //拒绝策略
);
try {
for (int i = 1; i <= 2; i++) {
threadPool.execute(()->{
System.out.println(Thread.currentThread().getName());
});
}
} catch (Exception e) {
e.printStackTrace();
} finally {
threadPool.shutdown();
}
}
}
When the number of for loops is set to 2:
At this time, the number of core threads is sufficient.
When the number of for loops is set to 4:
At this time, the number of core threads is not enough, but there are only 2 more threads, and the size of the blocking queue is 3, which is enough to store the 2 more threads, so there are still only two threads Running.
When the number of for loops is set to 6:
At this time, the number of core threads is not enough, there are 4 more threads, and the size of the blocking queue is 3, which is not enough to store the 4 extra threads, so more than two threads are running .
When the number of for loops is set to 19: the
maximum carrying capacity is the maximum number of threads + the number of blocking queues = 7+3 =10.
At this time, the maximum carrying capacity has been exceeded, and this rejection strategy will report a rejection exception.
pool-1-thread-1
pool-1-thread-3
pool-1-thread-2
pool-1-thread-3
pool-1-thread-4
pool-1-thread-2
pool-1-thread-1
pool-1-thread-2
pool-1-thread-5
pool-1-thread-4
pool-1-thread-4
pool-1-thread-3
pool-1-thread-4
pool-1-thread-7
pool-1-thread-5
pool-1-thread-2
pool-1-thread-6
pool-1-thread-1
java.util.concurrent.RejectedExecutionException: Task com.add.ExecutorsTest2$$Lambda$1/668386784@10f87f48 rejected from java.util.concurrent.ThreadPoolExecutor@b4c966a[Running, pool size = 7, active threads = 3, queued tasks = 0, completed tasks = 15]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
at com.add.ExecutorsTest2.main(ExecutorsTest2.java:30)
Process finished with exit code 0