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Common thread methods and daemon threads

2022-07-01 04:01:00 【Sit at a sunny window and drink tea alone】

Common methods

Method name	static	Functional specifications	Be careful
start()		Start a new thread , Run in a new thread run The code in the method	start The method is simply to put the thread into ready , The code doesn't have to run immediately （CPU I haven't given it a time slice yet ）. Per thread object start Method can only be called once , If called more than once, it will appear IllegalThreadStateException
run()		The method that will be called after the new thread starts	If in construction Thread Object Runnable Parameters , Called after the thread starts Runnable Medium run Method , Otherwise, no operation will be performed by default . But it can be created Thread Subclass object of , To override the default behavior
join()		Wait for the thread to finish running
join(long n)		Wait for the thread to finish running , Waiting for the most n millisecond
getId()		Get thread length integer id	id only
getName()		Get the thread name
setName(String)		Modify the thread name
getPriority()		Get thread priority
setPriority(int)		Modify thread priority	java The thread priority specified in is 1~10 The integer of , A higher priority can improve the thread's performance CPU Scheduling probability
getState()		Get thread status	Java Thread status in 6 individual enum Express , Respectively ：NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED
isInterrupted()		Judge whether it is interrupted	It won't clear Break mark
isAlive()		Is the thread alive （ Not finished yet ）
interrupt()		Interrupt thread	If the interrupted thread is sleep,wait,join It will cause the interrupted thread to throw InterruptedException, And clear the break mark ; If you interrupt a running thread , Will set up Break mark ;park Thread interrupted , Break marks will also be set
interrupted()	static	Determine whether the current thread is interrupted	Will clear Break mark
currentThread()	static	Get the currently executing thread
sleep(long n)	static	static Hibernate the currently executing thread n millisecond , Give up when dormant cpu Time slice to other threads
yield()	static	Prompt the thread scheduler to give up the current thread pair CPU Use	Mainly for testing and debugging

start And run

start The method is simply to put the thread into ready , The code doesn't have to run immediately （CPU I haven't given it a time slice yet ）. Per thread object start Method can only be called once , If called more than once, it will appear IllegalThreadStateException

Test code :

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.io.FileReader;

/** * @author  Wang Tianci  * @title: TestStartAndRun * @projectName hm-juc-codes * @description:  test start And run Method  * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-21 15:13 */
@Slf4j(topic = "c.TestStartAndRun")
@SuppressWarnings("all")
public class TestStartAndRun {
    

    /** *  Analog read  */
    public static void reader() {
    
        long start = System.currentTimeMillis();
        int sum = 0;
        for (int i = 0; i < 10000_000_00; i++) {
    
            sum += sum;
        }
        long end = System.currentTimeMillis();
        log.debug("reader cost {} ms ... ", (end - start));
    }

    public static void main(String[] args) {
    

        Thread t1 = new Thread("t1") {
    
            @Override
            public void run() {
    
                //  Get the name of the current thread 
                log.debug("{} running ... ", Thread.currentThread().getName());
                reader();
            }
        };

        t1.start();
        log.debug("do other thing ... ");
    }
}

Running results

C:\dev\Java\jdk1.8.0_152\bin\java.exe -javaagent:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=6195:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\dev\Java\jdk1.8.0_152\jre\lib\charsets.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\deploy.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\javaws.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jce.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfr.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jsse.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\management-agent.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\plugin.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\resources.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\rt.jar;F:\JavaCode\hm-juc-codes\juc-case-01\target\classes;F:\MavenRepo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;F:\MavenRepo\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;F:\MavenRepo\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;F:\MavenRepo\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;F:\MavenRepo\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;F:\MavenRepo\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;F:\MavenRepo\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar;F:\MavenRepo\org\openjdk\jmh\jmh-java-benchmark-archetype\1.35\jmh-java-benchmark-archetype-1.35.jar cn.knightzz.example.e2.method.TestStartAndRun
16:07:46.045 [main] DEBUG c.TestStartAndRun - do other thing ... 
16:07:46.045 [t1] DEBUG c.TestStartAndRun - t1 running ... 
16:07:46.301 [t1] DEBUG c.TestStartAndRun - reader cost 254 ms ... 

Process finished with exit code 0

As shown in the above running results :

t1 The thread does not execute immediately after it is started , Instead, it executes the method of the main thread , After that t1 Thread method
Be careful running yes t1 thread-executed !
t1 Threads and main threads execute in parallel !

While using run Execution time , running yes stay Executed by the main thread , There is no new thread !

Code instance :

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

@Slf4j(topic = "c.TestStartStatus")
@SuppressWarnings("all")
public class TestStartStatus {
    

    public static void main(String[] args) {
    
        Thread t1 = new Thread("t1") {
    
            @Override
            public void run() {
    
                //  Get the name of the current thread 
                log.debug("{} running ... ", Thread.currentThread().getName());
            }
        };

        log.debug("t1 : {} " , t1.getState());
        t1.start();
        log.debug("t1 : {} " , t1.getState());

    }
}

Execution results :

C:\dev\Java\jdk1.8.0_152\bin\java.exe -javaagent:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=14539:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\dev\Java\jdk1.8.0_152\jre\lib\charsets.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\deploy.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\javaws.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jce.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfr.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jsse.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\management-agent.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\plugin.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\resources.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\rt.jar;F:\JavaCode\hm-juc-codes\juc-case-01\target\classes;F:\MavenRepo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;F:\MavenRepo\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;F:\MavenRepo\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;F:\MavenRepo\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;F:\MavenRepo\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;F:\MavenRepo\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;F:\MavenRepo\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar;F:\MavenRepo\org\openjdk\jmh\jmh-java-benchmark-archetype\1.35\jmh-java-benchmark-archetype-1.35.jar cn.knightzz.example.e2.method.TestStartStatus
17:28:18.600 [main] DEBUG c.TestStartStatus - t1 : NEW 
17:28:18.604 [main] DEBUG c.TestStartStatus - t1 : RUNNABLE 
17:28:18.604 [t1] DEBUG c.TestStartStatus - t1 running ... 

Process finished with exit code 0

You can see the above execution results and code , When executed start() After method , The state of the thread changes from NEW Turned into RUNNABLE

summary :

Call directly run It is executed in the main thread run, No new thread started
Use start Is to start a new thread , Indirect execution through new threads run The code in

sleep And yield

sleep

call sleep Will cause the current thread to Running Get into Timed Waiting state （ Blocking ）
The current thread can use interrupt Method to interrupt the sleeping thread , At this time sleep Method will throw InterruptedException
After sleep, the thread may not be executed immediately
Suggest using TimeUnit Of sleep Instead of Thread Of sleep For better readability

sleep state

Code example :

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

@Slf4j(topic = "c.TestSleep")
@SuppressWarnings("all")
public class TestSleep {
    

    public static void main(String[] args){
    


        Thread t1 = new Thread("t1") {
    
            @Override
            public void run() {
    
                log.debug("t1 running ... ");
                log.debug("into sleep ... ");
                //  The current thread sleeps 
                try {
    
                    Thread.sleep(100);
                } catch (InterruptedException e) {
    
                    log.debug("t1 wake up ... ");
                    throw new RuntimeException(e);
                }
            }
        };

        log.debug("t1 status is {} ... " , t1.getState());
        t1.start();
        log.debug("t1 status is {} ... " , t1.getState());
        //  Interrupt other sleeping threads 
        log.debug("do other things ... ");
    }
}
C:\dev\Java\jdk1.8.0_152\bin\java.exe -javaagent:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=6691:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\dev\Java\jdk1.8.0_152\jre\lib\charsets.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\deploy.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\javaws.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jce.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfr.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jsse.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\management-agent.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\plugin.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\resources.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\rt.jar;F:\JavaCode\hm-juc-codes\juc-case-01\target\classes;F:\MavenRepo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;F:\MavenRepo\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;F:\MavenRepo\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;F:\MavenRepo\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;F:\MavenRepo\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;F:\MavenRepo\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;F:\MavenRepo\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar;F:\MavenRepo\org\openjdk\jmh\jmh-java-benchmark-archetype\1.35\jmh-java-benchmark-archetype-1.35.jar cn.knightzz.example.e2.method.TestSleep
20:01:43.076 [main] DEBUG c.TestSleep - t1 status is NEW ... 
20:01:43.079 [main] DEBUG c.TestSleep - t1 status is RUNNABLE ... 
20:01:43.079 [main] DEBUG c.TestSleep - do other things ... 
20:01:43.079 [t1] DEBUG c.TestSleep - t1 running ... 
20:01:43.079 [t1] DEBUG c.TestSleep - into sleep ... 

Process finished with exit code 0

figure

The reason for the main thread to sleep is because prevent t1 The thread is not sleeping yet , t1 The status information of the thread has been printed out , here t1 The state of the thread is still RUNNABLE

sleep interrupt

Code example :

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

/** * @author  Wang Tianci  * @title: TestInterceptor * @projectName hm-juc-codes * @description:  test sleep interrupt  * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-21 20:39 */
@Slf4j(topic = "c.TestSleep")
@SuppressWarnings("all")
public class TestInterceptor {
    

    public static void main(String[] args) throws InterruptedException {
    

        Thread t1 = new Thread("t1") {
    
            @Override
            public void run() {
    
                log.debug("t1 running ... ");
                //  The current thread sleeps 
                try {
    
                    log.debug("start sleep ... ");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
    
                    log.debug("t1 wake up ... ");
                    throw new RuntimeException(e);
                }
            }
        };

        t1.start();
        //  The main thread sleep is to ensure that  t1  Thread executing  interrupt  Method is already sleeping 
        Thread.sleep(1000);
        t1.interrupt();
        log.debug("do other things ... ");

    }
}
C:\dev\Java\jdk1.8.0_152\bin\java.exe -javaagent:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=6365:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\dev\Java\jdk1.8.0_152\jre\lib\charsets.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\deploy.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\javaws.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jce.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfr.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jsse.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\management-agent.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\plugin.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\resources.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\rt.jar;F:\JavaCode\hm-juc-codes\juc-case-01\target\classes;F:\MavenRepo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;F:\MavenRepo\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;F:\MavenRepo\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;F:\MavenRepo\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;F:\MavenRepo\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;F:\MavenRepo\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;F:\MavenRepo\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar;F:\MavenRepo\org\openjdk\jmh\jmh-java-benchmark-archetype\1.35\jmh-java-benchmark-archetype-1.35.jar cn.knightzz.example.e2.method.TestInterceptor
20:51:30.022 [t1] DEBUG c.TestSleep - t1 running ... 
20:51:30.024 [t1] DEBUG c.TestSleep - start sleep ... 
20:51:31.023 [t1] DEBUG c.TestSleep - t1 wake up ... 
20:51:31.023 [main] DEBUG c.TestSleep - do other things ... 
Exception in thread "t1" java.lang.RuntimeException: java.lang.InterruptedException: sleep interrupted
	at cn.knightzz.example.e2.method.TestInterceptor$1.run(TestInterceptor.java:30)
Caused by: java.lang.InterruptedException: sleep interrupted
	at java.lang.Thread.sleep(Native Method)
	at cn.knightzz.example.e2.method.TestInterceptor$1.run(TestInterceptor.java:27)

The running result is as above , You can see , t1 The thread is sleeping 1s in the future , He was interrupted

TimeUnit Sleep

Increase readability

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import javax.swing.*;
import java.util.concurrent.TimeUnit;

/** * @author  Wang Tianci  * @title: TestUnit * @projectName hm-juc-codes * @description:  test TimeUnit * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-21 20:59 */
@Slf4j(topic = "c.TestTimeUnit")
@SuppressWarnings("all")
public class TestTimeUnit {
    

    public static void main(String[] args) throws InterruptedException {
    

        log.debug("start ...");
        TimeUnit.SECONDS.sleep(10);
        // Thread.sleep()
        log.debug("end ...");

    }
}

yield

call yield Will cause the current thread to Running Get into Runnable Ready state , Then schedule other threads.
The specific implementation depends on the task scheduler of the operating system
The purpose is to put the current thread CPU Let the executive power go , however CPU Next time, you may give the time slice to

Thread priority

Thread priority will prompt （hint） The scheduler schedules the thread first , But it's just a hint , The scheduler can ignore it
If cpu Busy , The thread with higher priority will get more timeslices , but cpu Leisure time , Priority has little effect

CPU Idle situation

Code example :

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

/** * @author  Wang Tianci  * @title: TestPriority * @projectName hm-juc-codes * @description:  Test process priority  * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-22 20:33 */
@SuppressWarnings("all")
@Slf4j(topic = "c.TestPriority")
public class TestPriority {
    

    public static void main(String[] args) {
    

        Runnable task1 = new Runnable() {
    
            @Override
            public void run() {
    
                log.debug("task1 running ... ");
            }
        };

        Runnable task2 = new Runnable() {
    
            @Override
            public void run() {
    
                log.debug("task2 running ... ");
            }
        };

        Thread t1 = new Thread(task1, "t1");
        Thread t2 = new Thread(task2, "t1");

        //  set priority 
        t1.setPriority(Thread.MAX_PRIORITY);

        t1.start();
        t2.start();

        log.debug("main ended ... ");
    }
}

C:\dev\Java\jdk1.8.0_152\bin\java.exe -javaagent:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=8641:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\dev\Java\jdk1.8.0_152\jre\lib\charsets.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\deploy.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\javaws.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jce.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfr.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jsse.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\management-agent.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\plugin.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\resources.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\rt.jar;F:\JavaCode\hm-juc-codes\juc-case-01\target\classes;F:\MavenRepo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;F:\MavenRepo\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;F:\MavenRepo\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;F:\MavenRepo\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;F:\MavenRepo\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;F:\MavenRepo\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;F:\MavenRepo\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar;F:\MavenRepo\org\openjdk\jmh\jmh-java-benchmark-archetype\1.35\jmh-java-benchmark-archetype-1.35.jar cn.knightzz.example.e2.method.TestPriority
20:38:32.626 [main] DEBUG c.TestPriority - main ended ... 
20:38:32.626 [t1] DEBUG c.TestPriority - task2 running ... 
20:38:32.626 [t1] DEBUG c.TestPriority - task1 running ... 

Process finished with exit code 0

You can see , The results of the above run : Even though t1 The thread sets the maximum priority , But it will still appear t2 The thread runs first

CPU A busy situation

however If When the thread is busy :

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

/** * @author  Wang Tianci  * @title: TestPriority * @projectName hm-juc-codes * @description:  Test process priority  * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-22 20:33 */
@SuppressWarnings("all")
@Slf4j(topic = "c.TestPriority")
public class TestPriority {
    

    public static void main(String[] args) {
    

        Runnable task1 = new Runnable() {
    
            @Override
            public void run() {
    
                // log.debug("task1 running ... ");
                int count = 0;
                while (true) {
    
                    Thread.yield();
                    log.debug("task1 ==================> {}", count);
                    count++;
                }
            }
        };

        Runnable task2 = new Runnable() {
    
            @Override
            public void run() {
    
                int count = 0;
                while (true) {
    
                    Thread.yield();
                    log.debug("task2 ==================> {}", count);
                    count++;
                }
            }
        };

        Thread t1 = new Thread(task1, "t1");
        Thread t2 = new Thread(task2, "t1");

        //  set priority 
        t1.setPriority(Thread.MAX_PRIORITY);

        t1.start();
        t2.start();

        log.debug("main ended ... ");
    }
}

As can be seen above , task1 The number of is higher than task2 The number is big , explain task1 obtain CPU There are many times of time slice

join Methods,

join Method waits for the corresponding thread to end , such as t1.join() The effect is to wait t1 Thread end

Case study 1 General situation

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

@SuppressWarnings("all")
@Slf4j(topic = "c.TestJoin")
public class TestJoin {
    

    private static int value = 0;

    public static void main(String[] args) throws InterruptedException {
    

        method1();

    }

    private static void method1() throws InterruptedException {
    
        log.debug("method1 start ... ");
        Thread t1 = new Thread(() -> {
    
            try {
    
                log.debug("sleep start ... ");
                TimeUnit.SECONDS.sleep(1);
                value = 10;
                log.debug("sleep end ... ");
            } catch (InterruptedException e) {
    
                throw new RuntimeException(e);
            }
        });

        t1.start();
        log.debug("value  result  {} ", value);
        log.debug("main end ... ");
    }
}
C:\dev\Java\jdk1.8.0_152\bin\java.exe -javaagent:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=5463:D:\DevApp\JetBrain\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\dev\Java\jdk1.8.0_152\jre\lib\charsets.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\deploy.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\javaws.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jce.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfr.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\jsse.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\management-agent.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\plugin.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\resources.jar;C:\dev\Java\jdk1.8.0_152\jre\lib\rt.jar;F:\JavaCode\hm-juc-codes\juc-case-01\target\classes;F:\MavenRepo\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;F:\MavenRepo\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;F:\MavenRepo\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;F:\MavenRepo\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;F:\MavenRepo\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;F:\MavenRepo\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;F:\MavenRepo\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;F:\MavenRepo\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar;F:\MavenRepo\org\openjdk\jmh\jmh-java-benchmark-archetype\1.35\jmh-java-benchmark-archetype-1.35.jar cn.knightzz.example.e2.method.TestJoin
21:56:45.562 [main] DEBUG c.TestJoin - method1 start ... 
21:56:45.594 [Thread-0] DEBUG c.TestJoin - sleep start ... 
21:56:45.594 [main] DEBUG c.TestJoin - value  result  0 
21:56:45.595 [main] DEBUG c.TestJoin - main end ... 
21:56:46.606 [Thread-0] DEBUG c.TestJoin - sleep end ... 

Process finished with exit code 0

You can see the results above , Output value The value is 0, This is because the main thread and t1 Threads execute in parallel , There is no such thing as who waits

Case study 2 join

We can use join To wait for the thread to end

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

@SuppressWarnings("all")
@Slf4j(topic = "c.TestJoin")
public class TestJoin {
    

    private static int value = 0;

    public static void main(String[] args) throws InterruptedException {
    

        method1();

    }

    private static void method1() throws InterruptedException {
    
        log.debug("method1 start ... ");
        Thread t1 = new Thread(() -> {
    
            try {
    
                log.debug("sleep start ... ");
                TimeUnit.SECONDS.sleep(1);
                value = 10;
                log.debug("sleep end ... ");
            } catch (InterruptedException e) {
    
                throw new RuntimeException(e);
            }
        });

        t1.start();
        t1.join();
        log.debug("value  result  {} ", value);
        log.debug("main end ... ");
    }
}

From the caller's point of view :

Need to wait for the result to return , What can be continued is Sync
What you can continue to execute without waiting for the result to return is asynchronous

Case study 3 join Method

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

@SuppressWarnings("all")
@Slf4j(topic = "c.TestJoin2")
public class TestJoin2 {
    

    private static int value = 0;

    public static void main(String[] args) throws InterruptedException {
    

        Thread t1 = new Thread(){
    
            @Override
            public void run() {
    

                try {
    
                    //  sleep  1s
                    TimeUnit.SECONDS.sleep(1);
                    //  modify  value  Value 
                    value = 10;
                } catch (InterruptedException e) {
    
                    throw new RuntimeException(e);
                }
            }
        };

        Thread t2 = new Thread(){
    
            @Override
            public void run() {
    

                try {
    
                    //  sleep  1s
                    TimeUnit.SECONDS.sleep(2);
                    //  modify  value  Value 
                    value = 20;
                } catch (InterruptedException e) {
    
                    throw new RuntimeException(e);
                }
            }
        };

        t1.start();
        t2.start();
        t1.join();
        t2.join();

        log.debug("value : {} " , value);
        log.debug("do other thing ... ");
    }
}

ask : The execution time of the above code is 3s still 2s ?

Case study 4 Time limited join

We can specify the waiting time by specifying the incoming parameters : t1.join(3000);

package cn.knightzz.example.e2.method;

import cn.knightzz.example.e1.test.Test2;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

@SuppressWarnings("all")
@Slf4j(topic = "c.TestJoin2")
public class TestJoin3 {
    

    static int value = 0;

    public static void main(String[] args) throws InterruptedException {
    

        Thread t1 = new Thread(){
    
            @Override
            public void run() {
    

                //  sleep  5s
                try {
    
                    TimeUnit.SECONDS.sleep(5);
                    value = 10;
                    log.debug("sleep end ... ");
                } catch (InterruptedException e) {
    
                    throw new RuntimeException(e);
                }
            }
        };

        t1.start();
        log.debug("thread start ... ");
        t1.join(3000);
        log.debug("value : {}", value);
        log.debug("join end ... ");

    }
}
C:\Dev\jdk8\bin\java.exe -javaagent:D:\DevApp\JetBrains\ToolBox\apps\IDEA-U\ch-0\221.5787.30\lib\idea_rt.jar=4754:D:\DevApp\JetBrains\ToolBox\apps\IDEA-U\ch-0\221.5787.30\bin -Dfile.encoding=UTF-8 -classpath C:\Dev\jdk8\jre\lib\charsets.jar;C:\Dev\jdk8\jre\lib\ext\access-bridge-64.jar;C:\Dev\jdk8\jre\lib\ext\cldrdata.jar;C:\Dev\jdk8\jre\lib\ext\dnsns.jar;C:\Dev\jdk8\jre\lib\ext\dtfj.jar;C:\Dev\jdk8\jre\lib\ext\dtfjview.jar;C:\Dev\jdk8\jre\lib\ext\jaccess.jar;C:\Dev\jdk8\jre\lib\ext\localedata.jar;C:\Dev\jdk8\jre\lib\ext\nashorn.jar;C:\Dev\jdk8\jre\lib\ext\sunec.jar;C:\Dev\jdk8\jre\lib\ext\sunjce_provider.jar;C:\Dev\jdk8\jre\lib\ext\sunmscapi.jar;C:\Dev\jdk8\jre\lib\ext\sunpkcs11.jar;C:\Dev\jdk8\jre\lib\ext\traceformat.jar;C:\Dev\jdk8\jre\lib\ext\zipfs.jar;C:\Dev\jdk8\jre\lib\jce.jar;C:\Dev\jdk8\jre\lib\jsse.jar;C:\Dev\jdk8\jre\lib\management-agent.jar;C:\Dev\jdk8\jre\lib\resources.jar;C:\Dev\jdk8\jre\lib\rt.jar;C:\Dev\jdk8\bin\Dll02.dll;K:\CodeSpace\HMCodeSpace\hm-juc-codes\juc-case-01\target\classes;D:\Repos\mavenRepos\org\projectlombok\lombok\1.18.22\lombok-1.18.22.jar;D:\Repos\mavenRepos\ch\qos\logback\logback-classic\1.2.10\logback-classic-1.2.10.jar;D:\Repos\mavenRepos\ch\qos\logback\logback-core\1.2.10\logback-core-1.2.10.jar;D:\Repos\mavenRepos\org\slf4j\slf4j-api\1.7.32\slf4j-api-1.7.32.jar;D:\Repos\mavenRepos\cn\hutool\hutool-all\5.7.20\hutool-all-5.7.20.jar;D:\Repos\mavenRepos\org\openjdk\jmh\jmh-core-benchmarks\1.35\jmh-core-benchmarks-1.35.jar;D:\Repos\mavenRepos\org\openjdk\jmh\jmh-core\1.35\jmh-core-1.35.jar;D:\Repos\mavenRepos\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;D:\Repos\mavenRepos\org\apache\commons\commons-math3\3.2\commons-math3-3.2.jar cn.knightzz.example.e2.method.TestJoin3
21:16:55.011 [main] DEBUG c.TestJoin2 - thread start ... 
21:16:58.017 [main] DEBUG c.TestJoin2 - value : 0
21:16:58.019 [main] DEBUG c.TestJoin2 - join end ... 
21:17:00.015 [Thread-3] DEBUG c.TestJoin2 - sleep end ... 

Process finished with exit code 0

As can be seen above

interrupt Methods,

interrupt sleep, wait, join The thread of

sleep, wait, join These methods will put the thread into a blocking state , interrupt sleep The thread of , The interrupt status is cleared ( The interrupt status is reset to false ), With sleep For example

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

/** * @author  Wang Tianci  * @title: TestInterrupt * @projectName hm-juc-codes * @description:  interrupt sleep Threads  * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-27 21:37 */
@SuppressWarnings("all")
@Slf4j(topic = "c.TestInterrupt")
public class TestInterrupt {
    


    public static void main(String[] args) throws InterruptedException {
    

        Thread t1 = new Thread(() -> {
    

            try {
    
                TimeUnit.SECONDS.sleep(5); // sleep, wait, join  After being interrupted ,  The break mark will be cleared 
            } catch (InterruptedException e) {
    
                throw new RuntimeException(e);
            }
        }, "t1");

        t1.start();

        //  Main thread sleep 1s ,  Ensure that when interrupted , t1 The thread has sleep
        TimeUnit.SECONDS.sleep(1);

        //  interrupt 
        t1.interrupt();
        //  Check the interruption status 
        log.debug(" Break mark  : {}" , t1.isInterrupted());

    }
}

As can be seen above , t1 The thread is interrupted during sleep , And the break flag is reset to false

t1.isInterrupted() If the thread has been interrupted, return true, Otherwise return to false, Interrupted threads in sleep will throw exceptions

Interrupt a normal thread

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

/** * @author  Wang Tianci  * @title: TestInterrupt2 * @projectName hm-juc-codes * @description:  Test interrupts normal threads  * @website <a href="http://knightzz.cn/">http://knightzz.cn/</a> * @github <a href="https://github.com/knightzz1998">https://github.com/knightzz1998</a> * @create: 2022-06-28 14:45 */
@SuppressWarnings("all")
@Slf4j(topic = "c.TestInterrupt2")
public class TestInterrupt2 {
    

    public static void main(String[] args) throws InterruptedException {
    

        Thread t1 = new Thread(() -> {
    
            while(true) {
    
                Thread thread = Thread.currentThread();
                boolean interrupted = thread.isInterrupted();
                if (interrupted) {
    
                    log.debug(" Interrupt state  : {} " , interrupted);
                    break;
                }
            }
        }, "t1");

        t1.start();
        //  Sleep for a second ,  Guarantee t1 The thread is running 
        TimeUnit.SECONDS.sleep(1);
        t1.interrupt();
    }
}

As can be seen above : The normal thread is interrupted while running , The interrupt status is true

The two phases of the model terminate

problem

In a thread t1 Interrupt the thread correctly t2 , And let t2 Threads have a way to handle interrupts

Wrong thinking

Using thread objects stop() Method to stop the thread
- stop Method will really kill the thread , If the thread locks the shared resource , Then when it is killed, it will never have a chance to release the lock , Other threads will never acquire locks
Use System.exit(int) Method to stop the thread
- The purpose is only to stop a thread , But this will stop the whole process

Two stage termination mode

https://blog.csdn.net/thetimelyrain/article/details/114587111

LockSupport.park() You can make the current thread block

package cn.knightzz.example.e2.method;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;

@SuppressWarnings("all")
@Slf4j(topic = "c.TestInterrupt2")
public class TestPark {
    

    public static void main(String[] args) throws InterruptedException {
    
        method1();
    }

    private static void method1() throws InterruptedException {
    

        Thread t1 = new Thread(() -> {
    

            log.debug("thread park ... ");
            LockSupport.park(); //  Pause current thread 
            log.debug("thread unpark ... ");
            log.debug(" Interrupt state  : {} " , Thread.currentThread().isInterrupted());
        }, "t1");

        t1.start();
        //  sleep 1s
        TimeUnit.SECONDS.sleep(1);
        //  interrupt  t1  Thread park
        t1.interrupt();
    }
}

You can see the above running results , Main thread sleep 1s in the future , Start interrupting

LockSupport.park(); Method details :

First execution park After being interrupted , isInterrupted Will turn into true
here , If called again park() Method cannot block the thread .

 private static void method1() throws InterruptedException {
    

        Thread t1 = new Thread(() -> {
    

            log.debug("thread park ... ");
            LockSupport.park(); //  Pause current thread 
            log.debug("thread unpark ... ");
            log.debug(" Interrupt state  : {} " , Thread.currentThread().isInterrupted());

            // park()  Method details  :
            // 1.  First execution park After being interrupted , isInterrupted  Will turn into  true
            // 2.  here ,  If called again  park()  Method cannot block the thread .

            LockSupport.park();
            log.debug("thread unpark ... ");

        }, "t1");

        t1.start();
        //  sleep 1s
        TimeUnit.SECONDS.sleep(1);
        //  interrupt  t1  Thread park
        t1.interrupt();
    }

As can be seen above , When the thread is interrupted , Call again park Method cannot block a thread

have access to Thread.interrupted() Clear break status

 private static void method1() throws InterruptedException {
    

        Thread t1 = new Thread(() -> {
    

            log.debug("thread park ... ");
            LockSupport.park(); //  Pause current thread 
            log.debug("thread unpark ... ");
            log.debug(" Interrupt state  : {} " , Thread.currentThread().isInterrupted());

            // park()  Method details  :
            // 1.  First execution park After being interrupted , isInterrupted  Will turn into  true
            // 2.  here ,  If called again  park()  Method cannot block the thread .

            LockSupport.park();
            log.debug("thread unpark ... ");

            //  Clear break status 
            log.debug("clear interrupt status ... ");
            Thread.currentThread().interrupted();
            log.debug("thread park ... ");
            LockSupport.park();
            log.debug("thread unpark ... ");

        }, "t1");

        t1.start();
        //  sleep 1s
        TimeUnit.SECONDS.sleep(1);
        //  interrupt  t1  Thread park
        t1.interrupt();
    }

As can be seen above , After clearing the interrupt state , Call again park() Method , here Thread blocked

LockSupport.park summary

LockSupport.park() Used to block the current thread , And can be interrupt() Method break
First execution park After being interrupted , isInterrupted Will turn into true
here , If called again park() Method cannot block the thread .
But we can call Thread.currentThread().interrupted(); Clear thread break status

Not recommended

Methods not recommended , These methods are outdated , Easy to break synchronous code blocks , Cause thread deadlock :

stop() Stop the thread running
suspend() Hang up （ Pause ） Thread running
resume() Thread recovery

Main thread and guardian thread

By default ,Java process You need to wait for all threads to finish running , It's over . There is a special thread called the guardian thread , As long as other non daemon threads run , Even if the code of the daemon thread is not finished , It'll be forced to end .

package cn.knightzz.example.e2.thread;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

@SuppressWarnings("all")
@Slf4j(topic = "c.TestDaemon")
public class TestDaemon {
    

    public static void main(String[] args) throws InterruptedException {
    

        method1();

        TimeUnit.SECONDS.sleep(1);
        log.debug("main end ... ");
    }

    private static void method1() {
    

        Thread t1 = new Thread(() -> {
    

            log.debug("thread start ... ");
            try {
    
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
    
                throw new RuntimeException(e);
            }
            log.debug("thread end ... ");
        }, "t1");

        //  Set the current thread as the daemon thread 
        //  Be a daemon thread , As long as other non daemon threads run , Even if the code of the daemon thread is not finished , It'll be forced to end 
        t1.setDaemon(true);
        t1.start();
    }
}

Pictured above , According to the code above When t1 After thread start Sleep 3s Will execute the end , But because of t1 The thread is set as a daemon thread , therefore

When main After the method is over , Even if t1 The thread did not end execution , But it was also forced to shut down

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