In performance tests, the phrase “dump” is known. Stack dumps and thread dumps are useful tools for performing root cause analysis. Heap Dump and the analysis of it were already covered in the last post. Let’s go ahead and try to understand what a thread dump is and how to analyze it.
Thread Dump is a snapshot of the state of each thread at a given time, just like Heap Dump. To identify CPU spikes, deadlocks, slow response times, memory issues, unresponsive programs, and other system problems, thread dumps are an essential artifact. Finding out what each thread in the JVM is doing at any given time is made easier by using Thread Dump. Are there threads in a deadlock situation? Do all threads have activity? What threads are waiting for the resources that are stuck etc.? Thread dump analysis will provide the answers to all these questions.
Before we get started with the thread dump, let me introduce you to some basic terminology that will help you understand the idea behind it:
- Thread:
To achieve concurrency, a thread is a collection of instructions that can be processed simultaneously within the same program. JVM (Java Virtual Machine), which is dedicated to the operating system thread, also known as the native thread, is responsible for managing all Java threads. Threads work like lightweight processes and help enable many actions within a single process. Each thread has its own name, category, and unique identifier. Some of the fundamental components of a thread are:- A process is slower and heavier than a thread.
- Since the threads share the same address space, they can exchange data and program code.
- Context switching is generally cheaper between threads than between processes.
- Compared with process intercommunication, the cost of thread intercommunication is relatively cheap.
- Threads allow multiple tasks to run simultaneously.
- Multiple threads:
Java is a multithreaded program that allows multiple threads to run simultaneously. To handle multiple concurrent users and achieve multi-threading, a web server needs tens or hundreds of threads. However, a deadlock occurs when two or more threads use the same resources. - Deadlock:
Deadlock occurs when two or more threads wait for the completion of the other threads’ jobs before continuing their own jobs. A thread dump is needed to find the source of the deadlock.
Let’s look at an example where thread A owns resource X and needs resource Y, but thread B blocks it. When thread A locks resource X, thread B wants it at the same time. The result is that a program stops and does not advance. - Thread dump:
State the definition again. The state of all threads is recorded in a thread dump at any given time. It is useful to know what each thread in the JVM is doing at any given time. Are there threads in a deadlock situation? Do all threads have activity? What threads are waiting for the resources that are stuck etc.? Thread dump analysis will provide the answers to all these questions.
We’ll talk about the thread lifecycle in the next post.
