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.
-- https://gitlab.winehq.org/wine/wine/-/merge_requests/1628#note_23445