RFR(xxs): 8213236: A partial removed/deleted JavaThread cannot transition

[Robbin Ehn]

Thanks Erik!

/Robbin

On 01/11/2018 14:53, Erik Österlund wrote:
> Hi Robbin,
> 
> Looks good.
> 
> Thanks,
> /Erik
> 
> On 2018-11-01 12:57, Robbin Ehn wrote:
>> Hi all please review,
>>
>> In 8212933 we moved the cancellation of a handshake to the VM thread, for sanity
>> an assert was added to make sure the JavaThread do not cancel. (technically this
>> works also, but to keep a simple model it should be done by the VM thread)
>>
>> A JavaThread that is terminated but not yet free should not follow the safepoint
>> protocol. Since the VM thread running the safepoint cannot see such a thread
>> it's confusing and error-prone doing safepoint checks and transitions from a
>> thread not 'attached' to the VM.
>>
>> Issue:
>> https://bugs.openjdk.java.net/browse/JDK-8213236
>>
>> Code:
>> diff -r 13ad2bfee99e src/hotspot/share/runtime/vmThread.cpp
>> --- a/src/hotspot/share/runtime/vmThread.cpp    Thu Nov 01 09:57:57 2018 +0100
>> +++ b/src/hotspot/share/runtime/vmThread.cpp    Thu Nov 01 12:40:47 2018 +0100
>> @@ -319,7 +319,9 @@
>>  // Notify the VMThread that the last non-daemon JavaThread has terminated,
>>  // and wait until operation is performed.
>>  void VMThread::wait_for_vm_thread_exit() {
>> -  { MutexLocker mu(VMOperationQueue_lock);
>> +  assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
>> +  assert(((JavaThread*)Thread::current())->is_terminated(), "Should be off 
>> threadslist");
>> +  { MutexLockerEx mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
>>      _should_terminate = true;
>>      VMOperationQueue_lock->notify();
>>    }
>>
>> Passes t1-2.
>>
>> Thanks Robbin
>