Hi Chris, We're not tearing down the entire application. The HTTP server is just one part of our application (all part of the same JVM), and that is why calling the System.gc() on the teardown of the HTTP server may be harmful to the rest of the application since it would be handling other types of traffic, and a stop-the-world GC is not OK at this point. Even the link that you shared as reference does say that it is a red flag to call explicitly use System.gc() in the code.
Regards, Manisha ________________________________ From: Christopher Schultz <ch...@christopherschultz.net> Sent: Friday, December 27, 2024 11:10:32 PM To: users@tomcat.apache.org <users@tomcat.apache.org> Subject: Re: System.gc() call in Tomcat 9.0.96 [You don't often get email from ch...@christopherschultz.net. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] Markus, On 12/27/24 12:16 PM, i...@flyingfischer.ch.INVALID wrote: > Manisha > > you may be able to disable explicit System.gc() via the java argument - > XX:+DisableExplicitGC. > > https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.baeldung.com%2Fjava-system-gc&data=05%7C02%7Cmanisha.subramanian%40ericsson.com%7C436c9760409b45d1915208dd269da14e%7C92e84cebfbfd47abbe52080c6b87953f%7C0%7C0%7C638709180636317993%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Abo3vFypYK2JNApVSr%2B7PT45Gl6HyYvYVg%2BYtZd%2FmF8%3D&reserved=0<https://www.baeldung.com/java-system-gc> But ... WHY? This is a situation that should really only occur once during the application lifecycle (when it's being shut-down). Typically at shut-down you really don't care if a GC is going to happen. Also, tearing-down an application typically generates ... a lot of garbage. So a GC is likely to happen, anyway, naturally. If your application is big and there is memory pressure (unlikely, since everything is coming down) or if the GC sees large de-allocations and takes an opportunity to tidy-up the heap, then you may even get a FULL GC when this is all happening. Finally, it's in there to avoid a JVM crash which is pretty much the worst thing that can happen to your application, even if it is shutting down. -chris > Am 27.12.24 um 17:55 schrieb Christopher Schultz: >> Manisha, >> >> On 12/27/24 2:45 AM, Manisha Subramanian wrote: >>> Details of our application are given below: >>> OS: RHEL 8.x [OpenSSL version: 1.1.1] >>> Configuration: We're using Tomcat as an HTTP Server, but it is >>> embedded as part of our application >>> Java version: Java 8u381 >>> >>> We're using Apache Tomcat 9.0.86 and are considering an update to >>> 9.0.98. During the update, we noticed this commit, where we saw a >>> System.gc() call: >>> Avoid possible crashes with OpenSSL * apache/tomcat@bb4a5a0 * >>> GitHub<https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fapache%2Ftomcat%2Fcommit%2F&data=05%7C02%7Cmanisha.subramanian%40ericsson.com%7C436c9760409b45d1915208dd269da14e%7C92e84cebfbfd47abbe52080c6b87953f%7C0%7C0%7C638709180636334448%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=EvBbX0hyEOssdnENeIoOne62f%2FhRS6Lvc%2F5Qx8CfI7A%3D&reserved=0 >>> bb4a5a08603d8e1d67b4249fe8c634571a6ec852>. >>> >>> If we choose to stop our HTTP server [and the JVM chooses to honor >>> this System.gc() call] it will not just affect Tomcat, but the entire >>> JVM and may cause issues to our application. >>> The commit message says it'll occur mostly with the Tomcat test suite >>> but the impacts of the gc call may affect the entire application. >> >> I would think that taking down Tomcat and/or its connectors (which is >> what you would be doing when AprLifecycleListener.terminateAPR is >> called) would have a much bigger impact on your application (like >> STOPPING it) than requesting garbage-collection (which happens all the >> time). >> >>> We were wondering why this System.gc() was added. Request you to >>> share your views. >> >> The gc() call was added to attempt to force the cleanup of resources >> that have an impact on native-library resources before terminating the >> native library (OpenSSL). It is intended to prevent native crashes >> (which typically terminate the JVM) in some edge cases. >> >> -chris >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org >> For additional commands, e-mail: users-h...@tomcat.apache.org >> --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
