Re: [PATCH v7 0/8] MR1628: ntdll: Implement Low Fragmentation Heap.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about dlls/ntdll/heap.c:
> +{
> - ULONG affinity = heap_current_thread_affinity();
> - struct block *block;
> - struct group *group;
> -
> - /* acquire a group, the thread will own it and no other thread can clear free bits.
> -
> * some other thread might still set the free bits if they are freeing blocks.
> -
> */
> - if (!(group = heap_acquire_bin_group( heap, flags, block_size, bin ))) return NULL;
> - group->affinity = affinity;
> -
> - /* serialize with heap_free_block_lfh: atomically set GROUP_FLAG_FREE when the free bits are all 0. */
> - if (group_find_free_block( group, block_size, &block ))
> -
>    InterlockedAnd( &group->free_bits, ~GROUP_FLAG_FREE );
> - else
> -
>    InterlockedCompareExchange( &group->free_bits, GROUP_FLAG_FREE, 0 );

Try reusing the `InterlockedCompareExchange`'s value instead.  Read free bits, compare against zero, do the cmpxchg if equal, and _then_ use its value for the if statement below.