On 2/3/2014 5:18 AM, Chris Hegarty wrote:
Hi,
An old issue has resurfaced because of a change in AWT. AWT, now, on
Mac OS X, attaches a system graphics thread to the running VM, using
JNI_AttachCurrentThread. This change can result in a NPE, if a
security manager is installed, and the security manager tries to print
the name of the current thread.
In this case, attaching a thread to the VM, the j.l.Thread
instance/oop is created by the VM in allocate_threadObj(), and then
its constructor is run. At this point almost everything has been
created for the thread, jni env, etc, so it can query currentThread()
to retrieve itself. (Note: this is unusual. Typically the thread
running the j.l.Thread constructor is not itself.) Since the
j.l.Thread oop was allocated directly by the VM, its fields, other
than those directly set by allocate_threadObj(), are not initialized.
The call out from Thread.init to the security manager is problematic
as the partially constructed thread can be retrieved through
Thread.currentThread. Some of our internal tests run into a problem
when the security manager tries to print the name of the thread, i.e.
NPE.
Clearly there are other concerns of accessing a partially constructed
thread, not just the thread name, but it seems reasonable to simply
move the setting of the name to the beginning of the init() method.
I propose the following change for JDK 9, with the intention of backport
exactly to JDK 8. Long term this should be revisited in JDK 9.
This looks okay as a short-term fix to address this particular issue
(accessing the name of a partially constructed Thread object).
Mandy
