Declare Windows imports jobserver depends on

[ChrisDenton]

Jobserver is specifying external functions without also declaring a dependency on the relevant import library that contains those functions. While kernel32 will often be linked by something, the same can not be said for advapi32. As a bonus this is mildly more efficient.

In the future we could use raw-dylib to avoid the need for import libs entirely (requires msrv to be 1.65+),

[weihanglo]

Thanks for the patch!

As a bonus this is mildly more efficient.

Out of curiosity, how does it get more efficient with this change?

[ChrisDenton]

I wrote a bit about something similar on zulip: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Link.20attribute.20on.20Windows/near/470532686

It's a super minor thing and almost certainly doesn't affect the performance of jobserver. In short, an extern block defaults to static linkage whereas #[link] defaults to dynamic linkage. Since this function is from a DLL we want dynamic linkage because the location of a function is stored at an address in the import table rather than a static function you can call directly.

Static linkage wouldn't work at all except import libraries add a "jump stub". That is a kinda of dummy function that just jumps to the real function. It's the equivalent to this:

fn CloseHandle(handle: HANDLE) -> BOOL {
    (*__imp_CloseHandle)(handle)
}

So there's an extra level of indirection. Like, I said it's super minor and only rarely matters.