After using the thread pool for so long, do you really know how to reasonably configure the number of threads?

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One 、 How to configure a reasonable number of threads in a thread pool

（1）CPU intensive ：

Definition ：CPU Intensive means that the task requires a lot of computation , And there's no blocking ,CPU Running at full speed .

CPU Intensive tasks are only in real multicore CPU It's possible to speed up （ Through multi-threading ）.

CPU Configure as few threads as possible for intensive tasks .

“CPU Configuration formula for the number of intensive threads ：(CPU Check the number +1) A pool of threads

（2）IO intensive ：

Definition ：IO intensive , That is, the task requires a lot of IO, A lot of congestion .

Running on a single thread IO Intensive tasks can lead to a waste of CPU Computing power is wasted waiting .

therefore IO Multithreading in intensive tasks can greatly speed up the running of programs , Even in a single core CPU On , This acceleration mainly takes advantage of the wasted blocking time .

The first configuration ：

because IO Intensive task threads do not always perform tasks , Configure as many threads as possible .

“ Configuration formula ：CPU Check the number * 2.

Second configuration mode ：

IO Intensive time , Most threads are blocked , Therefore, it is necessary to configure multiple threads .

“ Configuration formula ：CPU Check the number / (1 – Block coefficient )（0.8~0.9 Between ）

such as ：8 nucleus / (1 – 0.9) = 80 Number of threads

Two 、 Custom thread pool

package com.lxk.com;
import java.util.concurrent.*;
/**
 *  Custom thread pool 
 */
public class ThreadPoolDemoFour {
    public static void main(String[] args) {


        //  Custom thread pool 
        ExecutorService threadPool = new ThreadPoolExecutor(3,
                5,
                60,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(1),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());
        try {
            for (int i = 0; i < 10; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName() + "\t  Handle the business ");
                });


            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }
}

3、 ... and 、 The actual use JDK Which thread pool is built in ？

【 mandatory 】 Thread resources must be provided through the thread pool , It is not allowed to explicitly create threads in the application . explain ： The advantage of using thread pool is to reduce the time consumed in creating and destroying threads and the overhead of system resources , Solve the problem of insufficient resources . If you do not use thread pools , It may cause the system to create a large number of similar threads, leading to memory consumption or “ Over switching ” The problem of .

【 mandatory 】 Thread pools are not allowed Executors To create , But through ThreadPoolExecutor The way , This way of processing makes the students who write more clear about the running rules of the thread pool , Avoid the risk of resource depletion . explain ：Executors The disadvantages of the returned thread pool object are as follows ：

• FixedThreadPool and SingleThreadPool: The allowed request queue length is Integer.MAX_VALUE, A large number of requests may pile up , Which leads to OOM.

• CachedThreadPool and ScheduledThreadPool: The number of threads allowed to be created is Integer.MAX_VALUE, A large number of threads may be created , Which leads to OOM.

source ：lixinkuan.blog.csdn.net/article/details/94501073

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