On Thu, 16 Jun 2022 13:34:18 GMT, Alan Bateman <al...@openjdk.org> wrote:
> If several native threads attach to the VM at around the same time, and > before any threads get an automatically generated name are created, then the > VM may crash attempting to access the thread status. The issue exists for > native threads that attach explicitly with JNI AttachCurrentThread without a > thread name, or native threads that attach implicitly by using a function > pointer to do an up call. > > The issue that raises its head periodically is that native threads that JNI > attach do the initializaiton of the Thread object in the context of the > attaching thread. Great care must be taken because Java code is executing in > the context of a Thread that is not fully initialized. The right thing is > probably to create the Thread object in another thread, using the service > thread has been mentioned. The issue at this time arises when two or more > native threads attempt to attach without thread names at around the same > time. The first thread that needs an automatically generated name triggers > the loading and initialization of a helper class. If there are other threads > attaching at the same time then they may have to wait on the monitor which > can trigger the crash because the field holder with the thread status is not > created at this time. Crashes in monitor enter and notify have been observed. > Coleen has changed this code so that linking and initialization uses a mutex > (JDK-8288064) so this specific crash doesn't duplicate in the main line. The short term fix for openjdk/jdk19 is to reorder the initialization so that field holder with the thread status is created before setting the name. > > Creating a jtreg test with the conditions to duplicate this issue is > complicated. The jtreg main wrapper creates the main thread with an > automatically generated thread name before it runs the test main method. This > is the reason that the test needs to launch a new VM with the right setup to > exercise both explicit and implicit attach. Looks good. And I confirmed that the VM code will correctly handle a null name from the current Java thread. Thanks. ------------- Marked as reviewed by dholmes (Reviewer). PR: https://git.openjdk.org/jdk19/pull/28
