[Bug 54979] Futexes which protect memory allocation congest, causing 100x performance degradation

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=54979

--- Comment #12 from John Nagle  ---
There is an outer level of spinlock.

See summary here: 
https://forum.winehq.org/viewtopic.php?t=37688

As far as I can tell, this is not fine-grained locking. It's just one big lock
for the whole heap. That should be a short spinlock, which, if it times out,
causes a kernel-level lock and block.

The bottleneck is that when you realloc a buffer, the old one may have to be
recopied, and the heap is locked up during that period.