Skip to main content

Threads in Java - Daemon thread (Part 17)

Daemon threads run in the background and mostly created by JVM for performing background tasks such as Garbage Collection, and other housekeeping tasks.

Daemon threads are meant to serve user threads and are only needed when the user threads are running, they will not prevent JVM from exiting once all the user threads have completed their execution.

That's why infinite loops which typically exist in the Daemon threads, don't cause any problems, because any code, including the finally block, won't execute after the user threads have finished their execution. For this reason. daemon threads are not recommended for I/O tasks.

However, there is an exception to this rule. The poorly designed code in daemon threads can prevent JVM from exiting. For instance. calling Threads.join() on running daemon thread can block the shutdown of the application.

Properties

  1. Any thread created by the main thread is by default non-daemon because any thread inherits its daemon nature from its parent thread. Since main is a non-daemon thread, any thread created by it will also be a non-daemon thread.
  2. We can make a thread daemon by calling method setDaemon(true).
  3. Thread.setDaemon() can only be called before starting the thread. It will throw IllegalThreadStateException if the thread is already started.
  4. Daemon threads are useful for background supporting tasks such as garbage collection, releasing memory of unused objects and removing unwanted entries from the cache. Most of the JVM threads are daemon threads.
  5. It is an utmost low priority thread.

Code example

Below code represents the implementation of Daemon thread - 

Output


Count from Daemon: 0
Count from Daemon: 1
Main thread finishes

Here we can see that even if the Daemon thread is running, the program terminates as the main thread which is a daemon thread is terminated.

Conclusion

Congratulations!! 🙋 today we discussed Daemon thread with its implementation. I hope you enjoyed this post.

You can find the complete code of this project on my GitHub in this commit. Feel free to fork or open issues, if any.

I would love to hear your thoughts on this and would like have suggestions from you to make it better. 

Feel free to befriend me on FacebookTwitter or Linked In or say Hi by email.

Happy Coding 😊

Comments

Popular posts from this blog

Parsing XML using Retrofit

Developing our own type-safe HTTP library to interface with a REST API can be a real pain as we have to handle many aspects - making connections caching retrying failed requests threading response parsing error handling, and more.  Retrofit, on the other hand, is a well-planned, documented and tested library that will save you a lot of precious time and headaches. In this tutorial, we are going to discuss how we can parse the XML response returned from  https://timesofindia.indiatimes.com/rssfeedstopstories.cms  using the Retrofit library. To work with Retrofit, we need three classes -  Model class to map the JSON data Interfaces which defines the possible HTTP operations Retrofit.Builder class - Instance which uses the interface and the Builder API which allows defining the URL endpoint for the HTTP operation. Every method of the above interface represents on possible API call. The request type is specified by using appropriate annotations (GET, POST). The respon

Threads in Java - CountDownLatch (Part 12)

A CountDownLatch is a synchronizer which allows one thread to wait for one or more threads before starts processing. A good application of  CountDownLatch is in Java server-side applications where a thread cannot start execution before all the required services are started. Working A  CountDownLatch is initialized with a given count which is the number of threads it should wait for. This count is decremented by calling countDown() method by the threads once they are finished execution. As soon as the count reaches to zero, the waiting task starts running. Code Example Let us say we require three services, LoginService, DatabaseService and CloudService to be started and ready before the application can start handling requests. Output Cloud Service is up! Login Service is up! Database Service is up! All services are up. Now the waiting thread can start execution. Here, we can see that the main thread is waiting for all the three services to start before starting its own

Threads in Java - Masterclass (Part 0)

Threads in Java Multithreading is a way to introduce concurrency in a program. In any case, if there are parallel paths in our program (parts which do not depend on the result from another part), we can make use of multithreading. One should exploit this feature, especially with all these multiple core machines nowadays. Below are a few reasons why we should use multithreading - 1. Keep a process responsive There was once a time when you would print a document in MS Word and the application would freeze for an annoyingly long amount of time until the job finished. Eventually, Microsoft solved this problem by running a printing job parallel to the main thread/ GUI thread.  To be clear though, not only GUI apps but Network services have to keep an ear to the ground for new clients, dropped connections and cancellation requests. In either case, it is critical to do the heavy lifting on a secondary thread to keep the user satisfied. 2. Keep a processor busy Keeping a proc