On Mon, 24 Oct 2022 12:16:54 GMT, Coleen Phillimore <cole...@openjdk.org> wrote:
> This change adds an option **EnableWaitForParallelLoad** to enable the legacy > behavior where the VM will manage synchronization for multiple threads > loading the same class using a non-parallel capable class loader that have > released the class loader lock. The VM will break the class loader lock for > parallel threads trying to load the class, and wait for the first thread that > initiated loading the class to complete. The subsequent threads will use the > result of the first thread, rather than get a LinkageError: duplicate class > definition for loading the class without synchronization. > Releasing the class loader lock was a common workaround for class loaders > that used a non-hierarchical delegation scheme to avoid deadlock, before > parallel capable class loading was added. > https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/ClassLoader.html#registerAsParallelCapable() > > Tested with tier1-6 and internal applications. It would be a little clearer if the bug synopsis was "Deprecate and disable legacy ...". A couple of queries below, but otherwise this looks good - and it will be good to see this old workaround disappear. Thanks. src/hotspot/share/classfile/placeholders.cpp line 137: > 135: assert(action != PlaceholderTable::LOAD_INSTANCE || seen == NULL, > 136: "Only one LOAD_INSTANCE allowed at a time"); > 137: Unclear why this is removed? If disabling the new flag causes this fail then shouldn't the new flag form part of the condition? src/hotspot/share/classfile/systemDictionary.cpp line 597: > 595: double_lock_wait(current, lockObject); > 596: } else { > 597: return NULL; Not clear why we return NULL here rather than just falling through and retrying? ------------- PR: https://git.openjdk.org/jdk/pull/10832
