securedExecute(WebAppServletContext.java:2273) $ServletInvocationAction.wrapRun(WebAppServletContext.java:3730) (SecureRandom.java:433)Ĭom.topComponentMethodBbuggycompanyin(RootTracer.java:439) " ExecuteThread: '1' for queue: ' (self-tuning)'" waiting for BLOCKED Below is the stack trace of one of that 50 threads: In these 102 threads 50 threads are in the BLOCKED state due to ‘#randomUUID()’ API call. In the thread dump report, you can notice that there are 102 threads in total. (Note: in the thread dump report, we have changed the package name to ‘buggycompany’ to hide the identity of the application). It would give the better context of the problem. If you haven’t clicked on the hyperlink in the previous sentence, we request you do so. Here is a real-world thread dump report of an application that was suffering from this problem. Real world application – 50 threads BLOCKED in #randomUUID() API If your application uses ‘#randomUUID()’ API in a critical code path and there is a lack of entropy in the operating system, then multiple threads can enter into this BLOCKED state bringing your entire application to a grinding halt. When there is a slowdown, application threads which are calling this ‘#randomUUID()’ API call will be put in a BLOCKED state, and they wouldn’t be able to progress further. When there is a lack of ‘entropy’ in the operating system then random number generation will slow down. What does ‘entropy’ mean? Linux kernel uses certain techniques like user’s mouse movements, variance in the hardware fan noise, variance in the noise of the device drivers … to generate random numbers. #randomUUID() API internally uses ‘ entropy‘ in the operating system to generate a unique number. Let’s discuss this API in this post with a real-world example. Under certain circumstances, using this API can affect your application’s availability. Java developers tend to use ‘#randomUUID()’ API, to generate a UUID (Universally Unique Identifier) number (i.e., ‘b8bbcbed-ca07-490c-8711-5118ee0af2f9’).
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