RFR (S) JDK-8139651 JDK-8139651, ConcurrentG1Refine uses ints for many of its members that should be unsigned types

Joseph Provino joseph.provino at oracle.com
Thu Feb 18 18:44:01 UTC 2016



On 2/12/2016 6:49 PM, Kim Barrett wrote:
>> On Feb 11, 2016, at 6:58 PM, Joseph Provino <joseph.provino at oracle.com> wrote:
>>
>> Please review this small change from "int" to "size_t".
>>
>> CR:  https://bugs.openjdk.java.net/browse/JDK-8139651
>>
>> webrev:  http://cr.openjdk.java.net/~jprovino/8139651/webrev.00
> ------------------------------------------------------------------------------
>
> Copyrights need updating.
Okay.
>
> ------------------------------------------------------------------------------
>
> I think the types of the command line options should be changed to be
> consistent with their associated concurrent refinement values, e.g.
> G1ConcRefinementGreenZone should have the same type as
> ConcurrentG1Refine::_green_zone and the associated accessor functions.
>
> This would eliminate the need for some explicit type specifications
> for MIN2/MAX2 calls and such.
Sounds good.
>
> ------------------------------------------------------------------------------
>
> I think some of these numbers are semantically not so much "sizes" as
> "counts", and wonder if such might be better typed as uint or uintx
> rather than size_t.
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/concurrentG1RefineThread.cpp
>    70   _threshold = MIN2<size_t>(cg1r()->thread_threshold_step() * (_worker_id + 1) + cg1r()->green_zone(),
>    73   _deactivation_threshold = MAX2<size_t>(_threshold - cg1r()->thread_threshold_step(), cg1r()->green_zone());
>
> Are the explicit types for MIN2/MAX2 still needed here?  I think all
> the argument types are the same.
I'll fix that.
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/concurrentG1RefineThread.cpp
>   138         size_t curr_buffer_num = (size_t)dcqs.completed_buffers_num();
>
> Identity cast.
Will fix.
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/dirtyCardQueue.cpp
>   214   if ((size_t)_n_completed_buffers <= stop_at) {
>
> Identity cast.
Will fix.
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/dirtyCardQueue.cpp
>   222     if (_completed_buffers_head == NULL)
>   223       _completed_buffers_tail = NULL;
>
> [preexisting]
>
> Please add braces around the "then" clause.
okay.
>
> Perhaps better would be to change
>
>   222     if (_completed_buffers_head == NULL)
>   223       _completed_buffers_tail = NULL;
>   224     assert(_n_completed_buffers > 0, "Invariant");
>   225     _n_completed_buffers--;
>
> =>
>
>    assert(_n_completed_buffers > 0, "Invariant");
>    _n_completed_buffers--;
>    if (_completed_buffers_head == NULL) {
>      assert(_n_completed_buffers == 0, "Invariant");
>      _completed_buffers_tail = NULL;
>    }
Okay.
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/g1RemSet.cpp
>   294   size_t into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();
>
> Unused variable can just be removed.
okay.
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/ptrQueue.hpp
>   220   size_t _process_completed_threshold;
>   242   size_t _max_completed_queue;
>
> These variables cannot presently be changed to an unsigned type.  A
> negative value is treated specially for both of them, as a flag that
> turns off associated behavior.  A negative _max_completed_queue means
> there is no maximum.  A negative _process_completed_threshold means
> never trigger concurrent processing of completed buffers.  I think the
> -1 special values (converted to size_t) end up working and providing
> the desired behavior by accident, which would explain why these didn't
> lead to any test failures.
>
> This is a bit of a mess, and I've got a fix for it in progress.
>
> Unfortunately, undoing the type changes here might make a bit of a
> mess elsewhere, requiring additional ugly casts.
>
> For examples of the use of -1 for these, see the constructor for
> SATBMarkQueue (_max_completed_queue) and the initialize call for the
> non-Java-thread dirty card queue set in G1CollectedHeap::initialize
> (both are -1).
>
> ------------------------------------------------------------------------------
> src/share/vm/gc/g1/ptrQueue.cpp
>   261 size_t PtrQueueSet::completed_buffers_list_length() {
>   262   int n = 0;
>   263   BufferNode* cbn = _completed_buffers_head;
>   264   while (cbn != NULL) {
>   265     n++;
>   266     cbn = cbn->next();
>   267   }
>   268   return n;
>   269 }
>
> The type of n should also be changed to size_t.
okay.
>
> ------------------------------------------------------------------------------
>



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