RFR 8085965: VM hangs in C2Compiler

Thomas Schatzl thomas.schatzl at oracle.com
Thu Jun 11 13:28:49 UTC 2015


On Wed, 2015-06-10 at 14:20 -0700, Poonam Bajaj Parhar wrote:
> Please review the code changes to fix:
> JDK-8085965: VM hangs in C2Compiler 
> Problem and fix: 
> In JDK8, CMSClassUnloadingEnabled option which is used to control the
> class-unloading in CMS, was enabled by default. But if the user
> specifies -Xnoclassgc or -XX:-ClassUnloading on the command line then
> classes get unloaded but updating of subklasses/siblings links gets
> skipped by the ClassUnloading check in the following function:
> void Klass::clean_weak_klass_links(BoolObjectClosure* is_alive, bool 
>   clean_alive_klasses) { 
>    if (!ClassUnloading) { 
>      return; 
>    }
> which corrupts the class hierarchy links causing hangs and crashes. 
> This fix honors -XX:-ClassUnloading and -Xnoclassgc options and
> disables class unloading with CMS.
> Webrev: http://cr.openjdk.java.net/~poonam/8085965/webrev/

  it looks like this is the same problem as JDK-8059128 for G1 which has
been closed as Incomplete. The log attached to the CR also shows that
class unloading is disabled manually.

Could they be related after all?


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