This article will be of interest to you if you are seeing messages like this in a logfile, or printed to stdErr for your process:
These messages are not Errors. They are produced by a mechanism in the Zing Virtual Machine (ZVM) called the Safepoint Profiler. This helps you work out what's happening in your application when there are threads that take longer than a given threshold to reach a safepoint. The Safepoint Profiler is designed to have a minimal impact on your application, and Azul Support recommends that you keep it on so that you have the information you need to help diagnose time to safepoint issues if they occur.
When the ZVM needs to bring all running threads to a safepoint in order to perform some critical task, it notifies all the threads. Sometimes one or more of the threads will take longer than others to respond to the notification, and then the threads which responded to the request in a timely fashion are delayed.
What the Safepoint Profiler messages show you is the stacks for the late threads, and you can examine the stacks to work out what could be making the thread late to safepoint, and then take action to correct it in future.
There is a set of flags that you can use to control the Safepoint Profiler:
For more information on safepoint profiling, including a more detailed overview and advice on how to read the output, please consult the Safepoint Profiler section of the Zing User Guide.