Welcome to the Java Programming Forums


The professional, friendly Java community. 21,500 members and growing!


The Java Programming Forums are a community of Java programmers from all around the World. Our members have a wide range of skills and they all have one thing in common: A passion to learn and code Java. We invite beginner Java programmers right through to Java professionals to post here and share your knowledge. Become a part of the community, help others, expand your knowledge of Java and enjoy talking with like minded people. Registration is quick and best of all free. We look forward to meeting you.


>> REGISTER NOW TO START POSTING


Members have full access to the forums. Advertisements are removed for registered users.

Results 1 to 1 of 1

Thread: Simulating & troubleshooting BLOCKED threads in Kotlin

  1. #1
    Member
    Join Date
    Nov 2017
    Location
    USA
    Posts
    137
    Thanks
    6
    Thanked 1 Time in 1 Post

    Default Simulating & troubleshooting BLOCKED threads in Kotlin



    In this series of simulating and troubleshooting performance problems in Kotlin, let’s discuss how to make threads go into BLOCKED state. A thread will enter into a BLOCKED state when it couldn’t acquire a lock on an object because another thread already holds the lock on the same object and doesn’t release it.

    Video: To see the visual walk-through of this post, click below:

    https://youtu.be/czhLzcmZ_ME

    Kotlin blocked thread Program
    Here is a sample program, which would make threads go into BLOCKED state.
    package com.buggyapp
       class BlockedApp {
          fun start() {
             println("BlockedApp:started")
             for (counter in 0..9) { // Launch 10 threads.
                AppThread().start()
             }
          }
       }
     
       class AppThread : Thread() {
          override fun run() {
             AppObject.something
          }
       }
     
       object AppObject {
          @get:Synchronized 
          val something: Unit
             get() {
                while (true) {
                   try {
                      Thread.sleep(6000000.toLong())
                   } catch (e: Exception) {
                   }
                }
             }
       }
     
       fun main() {
          println(BlockedApp().start())
       }
    Sample program contains the ‘BlockedApp’ class. This class has a start() method. In this method, 10 new threads are created. In the AppThread class there is a run() method that invokes getSomething() method on the AppObject. In this getSomething() method, thread is put to continuous sleep i.e. thread is repeatedly sleeping for 10 minutes again and again. But if you notice, the getSomething() method is a synchronized method. Synchronized methods can be executed by only one thread at a time. If any other thread tries to execute the getSomething() method while the previous thread is still working on it, then the new thread will be put in the BLOCKED state.

    In this case, 10 threads are launched to execute the getSomething() method. However, only one thread will acquire lock and execute this method, remaining 9 threads will be put in BLOCKED state.

    NOTE: If threads are in BLOCKED state for a prolonged period, then application may become unresponsive.

    How to diagnose BLOCKED threads?
    You can diagnose BLOCKED threads either through a manual or automated approach.

    Manual approach
    In the manual approach, you need to capture thread dumps as the first step. A thread dump shows all the threads that are in memory and their code execution path. You can capture thread dump using one of the 8 options mentioned here. But an important criteria is: You need to capture thread dump right when the problem is happening (which might be tricky to do). Once the thread dump is captured, you need to manually import the thread dump from your production servers to your local machine and analyze it using thread dump analysis tools like fastThread, samurai.

    Automated approach
    On the other hand, you can also use yCrash open source script, which would capture 360-degree data (GC log, 3 snapshots of thread dump, heap dump, netstat, iostat, vmstat, top, top -H,…) right when the problem surfaces in the application stack and analyze them instantly to generate root cause analysis report.

    We used the automated approach. Below is the root cause analysis report generated by the yCrash tool highlighting the source of the problem.



    Fig: yCrash reporting transitive dependency graph of 9 BLOCKED threads

    yCrash prints a transitive dependency graph that shows which threads are getting BLOCKED and who is blocking them. In this transitive graph, you can see ‘Thread-0’ blocking 9 other threads. If you click on the thread names in the graph, you can see the stack trace of that particular thread.



    Fig: yCrash reporting the stack trace of 9 threads that are in BLOCKED state

    Here is the screenshot that shows the stack trace of the 9 threads which are in BLOCKED state and it’s also pointing out the stack trace in which they are stuck. From the stacktrace you can observe that thread is stuck on ‘com.buggyapp.blockedapp.AppObject#getSomething()’ method.

    Equipped with this information, one can easily identify the root cause of the BLOCKED state threads.
    Last edited by Ram Lakshmanan; March 21st, 2023 at 07:53 AM. Reason: SOME CORRECTIONS

Similar Threads

  1. Simulating & troubleshooting OOMError in Scala
    By Ram Lakshmanan in forum File Input/Output Tutorials
    Replies: 0
    Last Post: February 8th, 2023, 11:15 PM
  2. Simulating & troubleshooting StackOverflowError in Kotlin
    By Ram Lakshmanan in forum Java JDK & IDE Tutorials
    Replies: 0
    Last Post: January 18th, 2023, 04:29 AM
  3. Simulating & troubleshooting Thread leak in Kotlin
    By Ram Lakshmanan in forum Java Programming Tutorials
    Replies: 0
    Last Post: December 14th, 2022, 01:03 AM
  4. Simulating & troubleshooting OOMError in Kotlin
    By Ram Lakshmanan in forum Debugging Tutorials
    Replies: 0
    Last Post: November 10th, 2022, 07:28 AM
  5. Simulating & troubleshooting deadlock in Kotlin
    By Ram Lakshmanan in forum Java JDK & IDE Tutorials
    Replies: 0
    Last Post: September 29th, 2022, 11:42 PM