RFR: 8262271: SA: Add new stress test that tests getting the stack trace of an active thread

[Chris Plummer]

On Thu, 25 Feb 2021 03:54:35 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> This a new test that runs jstack on a process that is busy doing things. It runs jstack 4 times as the process is starting up.

> Sorry but I don't see how this ensures it runs jstack as the jshell is
> starting up, the startup could be complete before even one jstack gets
> issued.

My observation is that at least the main thread has a different stack trace on each iteration. Also, each iteration takes progressively longer as jshell starts up. Although I don't fully understand the reason why, I think it's related to [JDK-8262098](https://bugs.openjdk.java.net/browse/JDK-8262098). Possibly the larger the program gets, the more SA needs to page in, even though you would think jstack would not need to touch that many pages. In any case, this is an indication that the program is changing its state.

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PR: https://git.openjdk.java.net/jdk/pull/2720