[Animats]

I struggled with this in Wine. "malloc" type memory allocation involves at least two levels of spinlocks. When you do a "realloc", the spinlocks are held during the copying operation. If you use Vec .push in Rust, you do a lot of reallocs. In a heavily multithreaded program, this can knock performance down by more than two orders of magnitude. It's hard to reproduce this with a simple program; it takes a lot of concurrency to hit futex congesion.

Real Windows, and Linux, don't have this problem. Only Wine's "malloc" in a DLL, which does.

Bug reports resulted in finger-pointing and denial.[1] "Unconfirmed", despite showing debugger output.

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

[rendaw]

Reading the bug report, I don't see any denial. The maintainers are pretty clear that they acknowledge the issue, but don't know how to fix it.

[Animats]

Yes, although it took a while to get there. This confirms the OP's line "Spinning around: Please don't". You can get huge performance hits that are hard to fix. Huge.

[electroglyph]

Microsoft's rwlock implementation was borked up until sometime last year iirc. this stuff is difficult to do correctly