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I need to peek into the stack of 2 deadlocked threads to analyze the situation. The JVM is live right now and the data is there, but I need some kind of tool to extract it from the process. I only care about 6 variables in the stack of type String. Any ideas are greatly appreciated. JVM versions 6_35, it's a linux, JMX is enabled, but I dont have a profiler/debugger connection configured on it. It's very difficult to reproduce.
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To take a thread dump, navigate to the console used to launch the Java application, and press the CTRL and Break keys together. It's worth noting that, on some keyboards, the Break key isn't available. Therefore, in such cases, a thread dump can be captured using the CTRL, SHIFT, and Pause keys together.
Yes, thread dump and heap dump are stop-the-world operations in JDK 8. HotSpot JVM performs them at the global safepoint. See this and this answers for more information. Save this answer.
A thread dump is a snapshot of the state of all threads that are part of the process. The state of each thread is presented with a so called stack trace, which shows the contents of a thread's stack. Some of the threads belong to the Java application you are running, while others are JVM internal threads.
If it is a thread dump, then can we say a Heap Dump contains a Thread Dump? Hi Vish, Yes, some heap dumps contain also thread information.
I found a little trick using a heap dump viewer (YourKit in this instance, but may be others work as well). Basically you enumerate all instances of the Thread class, then you find the thread you want by name and open it. The stack variables are marked as < local variable > like this:
Not all variables are here, but all that are passed as arguments to method are displayed. I wonder if the profilers can address this issue even better?
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You can't do this easily. Normal jstack tool will only dump stack. Technically you can try dumping whole heap (using jmap) but looking for this particular variables can be a pain if possible.
Note that this is not easily doable for security reasons. Stack traces can contain credentials or other sensitive data.
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