This following post is based on the Udemy Course: Java Multithreading
UNDERSTANDING INTERRUPT USING CODE
The main thread pauses for 500 milliseconds (0.5 seconds) using Thread.sleep(500). This allows the t1 thread to run for a short time before the main thread interrupts it. After the pause, the main thread interrupts the t1 thread by calling t1.interrupt(). This sends an interrupt signal to the t1 thread, which can be used to gracefully stop the execution or handle the interruption.
The important thing to note in this example is that the t1 thread will still be able to complete what it’s doing. In the next code example, we will look at how to detect if the thread has been interrupted and take any necessary action.
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package com.threads;
import java.util.Random;
public class App {
public static void main(String[] args) throws InterruptedException {
System.out.println("Started.");
Thread t1 = new Thread(new Runnable() {
Random random = new Random();
@Override
public void run() {
//1E8 = 1x10^8
//this code will take a while to complete
for(int i=0; i<1E8; i++) {
Math.sin(random.nextDouble());
}
}
});
t1.start();
Thread.sleep(500);
t1.interrupt();
t1.join();
System.out.println("Finished.");
}
}
USING INTERRUPTS
Within each iteration of the loop in Thread t1, there is a check using Thread.currentThread().isInterrupted() to see if the current thread (t1) has been interrupted. If it has, the program prints the name of the current thread followed by “has been interrupted” and breaks out of the loop.
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package com.threads;
import java.util.Random;
public class App {
public static void main(String[] args) throws InterruptedException {
System.out.println(Thread.currentThread().getName() + " has started");
Thread t1 = new Thread(new Runnable() {
Random random = new Random();
@Override
public void run() {
for(int i=0; i<1E8; i++) {
if(Thread.currentThread().isInterrupted()) {
System.out.println(Thread.currentThread().getName() + " has been interrupted");
break;
}
Math.sin(random.nextDouble());
}
System.out.println(Thread.currentThread().getName() + " has finished.");
}
});
t1.start();
Thread.sleep(500);
t1.interrupt();
t1.join();
System.out.println(Thread.currentThread().getName() + " has finised");
}
}
OUTPUT:
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main has started
Thread-0 has been interrupted.
Thread-0 has finished.
main has finised
ADDING THREAD.SLEEP
In the below code, we have removed the check Thread.currentThread().isInterrupted(). But, we have added Thread.sleep() which internally checks the status of the thread if it’s interrupted. In that case, it will throw an InterruptedException.
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main has started
java.lang.InterruptedException: sleep interrupted
at java.base/java.lang.Thread.sleep(Native Method)
at thread101/com.threads.App$1.run(App.java:28)
at java.base/java.lang.Thread.run(Thread.java:829)
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package com.threads;
import java.util.Random;
public class App {
public static void main(String[] args) throws InterruptedException {
System.out.println(Thread.currentThread().getName() + " has started");
Thread t1 = new Thread(new Runnable() {
Random random = new Random();
@Override
public void run() {
for(int i=0; i<1E8; i++) {
/*
* if(Thread.currentThread().isInterrupted()) {
* System.out.println(Thread.currentThread().getName() +
* " has been interrupted."); break; }
*/
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
Math.sin(random.nextDouble());
}
System.out.println(Thread.currentThread().getName() + " has finished.");
}
});
t1.start();
Thread.sleep(500);
t1.interrupt();
t1.join();
System.out.println(Thread.currentThread().getName() + " has finised");
}
}