Thanks Mikael, Dmitry and Bengt!
On 4 dec 2013, at 13:53, Bengt Rutisson <[email protected]> wrote:
>
> Hi Staffan,
>
> Looks good.
>
> Thanks,
> Bengt
>
> On 2013-12-02 17:30, Staffan Larsen wrote:
>> The problem here happens when SA wants to walk every object in the heap, to
>> do that it needs to figure out what parts of the heap are in active use (the
>> "live regions"). It gets the list of GC spaces as a start. It then maps out
>> the TLABs in these spaces so that it will not walk un-allocated memory in
>> the TLABs.
>>
>> In this case, it misses one (or more) active TLABs and so tries to walk
>> memory that is part of a TLAB, but that has not been allocated to an object
>> yet. In a fast debug build this will be filled with 0xbaadbabe and while
>> dereferencing this memory it fails with a WrongTypeException. Sometimes it
>> will also fail with an UnmappedAddressException, but these exceptions are
>> ignored in this part of SA (for some reason).
>>
>> The TLAB that SA misses is one in a compiler thread. The code in SA does:
>>
>> if (VM.getVM().getUseTLAB()) {
>> for (JavaThread thread = VM.getVM().getThreads().first(); thread !=
>> null; thread = thread.next()) {
>> if (thread.isJavaThread()) {
>> ThreadLocalAllocBuffer tlab = thread.tlab();
>> ....
>>
>> The problem is that thread.isJavaThread() will return false for
>> CompilerThread (and some others) although they can have TLABs that we need
>> to look at. The solution is to remove that check.
>>
>> I’ve left some debugging code in place in the code that I think can be
>> useful for other problems. The real fix is just two lines of code.
>>
>> webrev: http://cr.openjdk.java.net/~sla/8029395/webrev.00/
>> bug: https://bugs.openjdk.java.net/browse/JDK-8029395
>>
>> Thanks,
>> /Staffan
>
