RFR: 8154715: Missing destructor and/or TLS clearing calls for terminating threads

[Brian Gardner]

I really like the rename of java_start to native_thread_entry, it makes things make more sense.  It looks like os_bsd.cpp and os_linux.cpp are both missing the clear_thread_current logic after thread->run().

+  // If a thread has not deleted itself ("delete this") as part of its
+  // termination sequence, we have to ensure thread-local-storage is
+  // cleared before we actually terminate. No threads should ever be
+  // deleted asynchronously with respect to their termination.
+  if (Thread::current_or_null_safe() != NULL) {
+    assert(Thread::current_or_null_safe() == thread, "current thread is wrong");
+    thread->clear_thread_current();
+  }
+

> On May 9, 2016, at 5:33 PM, David Holmes <david.holmes at oracle.com> wrote:
> 
> Okay here is version 2:
> 
> http://cr.openjdk.java.net/~dholmes/8154715/webrev.v2/
> 
> Lots of cosmetic changes but only a couple of functional ones:
> 
> -  After thread->run() returns we clear the TLS by calling clear_thread_current(), but only for threads where it has not already been cleared - as those threads may already have been deleted so we can't dereference 'thread'
> 
> - No asynchronous thread deletion is permitted, and we avoid races with VM termination. This means the VMThread no longer gets deleted - that should not be an issue as many threads do not get deleted when the VM terminates. I added destructors for the VMThread and WatcherThread so anyone introducing their deletion is informed by a guarantee(false)
> 
> 
> Cosmetic changes:
> 
> - renamed java_start to thread_native_entry (it is used by all threads not just "java" ones, so this avoids potential confusion)
> 
> - updated os::free_thread to always assume it works on the current thread (and add assert to verify that)
> 
> Thanks,
> David