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Difference between Daemon threads and user threads in Java
Ravi
Daemon threads
Daemon threads are low-priority threads whose purpose is to provide services to user threads.
User threads
User threads are high-priority threads whose purpose is to perform complex tasks that may or may not be supported by Daemon threads.
| Daemon Threads | User Threads |
|---|---|
| JVM never waits until all the user threads have completed their work. It exits as soon as all user threads have finished their work. | JVM never exits until all the user threads have completed their work. |
| The lifecycle of the Daemon threads is dependent on the user threads. | The lifecycle of user threads is independent. |
| JVM force stops/terminates the Daemon threads. | JVM does not force stop/terminate the user threads. |
| Daemon threads have a lower priority compared to user threads. | User threads have a higher priority compared to Daemon threads. |
| Daemon threads are service providers for user threads running in the same process. | User threads can use daemon thread services but are not entirely dependent on them. |
Example
public class Main{
public static void main(String[] args) throws InterruptedException {
Runnable daemonRunnable = () -> {
while(true){
System.out.println("I'm a daemon thread");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Runnable userRunnable = () -> {
try {
System.out.println("I'm a user thread");
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
};
Thread daemonThread = new Thread(daemonRunnable);
daemonThread.setName("daemon-thread");
daemonThread.setDaemon(true);
Thread notDaemonThread = new Thread(userRunnable);
notDaemonThread.setName("not-daemon-thread");
daemonThread.start();
notDaemonThread.start();
Thread.sleep(4000);
}
}Try it out!
Explanation
- Lines 4–13: We define a runnable called
daemonRunnableto run for the Daemon thread. We use awhileloop in the runnable function to print a string and sleep for one second. - Lines 15–22: We define a runnable called
userRunnableto run for the user thread. In the runnable function, we print a string and sleep for three seconds. - Lines 24–31: We create a Daemon and a user thread with the corresponding runnable.
After executing the code, we can observe that the Daemon thread is still in the running state, and prints “I’m a daemon thread,” while the user thread has completed running the runnable. Although the daemon thread is still running, the JVM exits.
Note: For more on Daemon threads in Java, refer to: How to create a daemon thread in Java and How to check if a thread is a daemon thread.
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java
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Ravi
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