add rust_trylock_little_lock

[toffaletti]

I need try_lock for an algorithm I'm trying to implement in Rust.

[alexcrichton]

How come this is explicitly checked?

[toffaletti]

EBUSY is what happens when the lock is already locked.

[alexcrichton]

Hm, I'd be more comfortable with a comment along the lines of:

// Explicitly return false on EBUSY (lock is already locked), but assert on all other errors

[toffaletti]

I've attempted to improve the readability.

[toffaletti]

I've fixed the compile error. I'm not able to compile and test this locally, which is why this happened. The error I get has something to do with stage0 snapshot not containing my changes to the C++ lib. I might have to split this into two changes. One to change the C++ lib and a later change to libstd?

[alexcrichton]

Oh I forgot to ask before, but could you expand the commit message a little bit? Just the standard short-title + 1-2 sentences after it explaining what's going on. Thanks!

[toffaletti]

@huonw Thanks, adding #[cfg(not(stage0))] before try_lock worked, but then my make check-stage1 failed at:

compile_and_link: x86_64-unknown-linux-gnu/stage0/lib/rustc/x86_64-unknown-linux-gnu/lib/librustpkg.so
/home/jason/rust/src/librustpkg/path_util.rs:476:12: 476:23 error: invoking non-Rust fn in fn without #[fixed_stack_segment], #[deny(cstack)] on by default
/home/jason/rust/src/librustpkg/path_util.rs:476             libc::chmod(src_buf, S_IRUSR as libc::mode_t) == 0
                                                             ^~~~~~~~~~~
error: aborting due to previous error

This was rebased off latest master.

@alexcrichton I updated the commit message, but before this is merged I'll probably need to rebase off master once the above issue is fixed.

[alexcrichton]

This doesn't look to be a snapshot problem, we rebuild the runtime for stage0. It looks like you're just missing the shim C function in the middle.

[toffaletti]

Sorry, two different problems. First I had a problem building stage0, which iirc was complaining about librustrt not containing rust_trylock_littlelock. This was related to my change and was fixed by the annotation suggested by huonw. Then I pulled in the latest master changes and like I said above, got a new error while running make check. This second error seems unrelated to my changes it just means my pull request won't build because I pulled in someone else's bug in librustpkg.

[toffaletti]

Looks like 65aacd0#diff-e16b4a8a6901a9937ee5627cfddb3590R474 fixes my second problem. I'll pull that in and try again tomorrow.

[toffaletti]

This should be good to merge now. I rebased off current master and it passed make check-stage1.

[alexcrichton]

Are you sure? I'm still not seeing a definition of rust_trylock_little_lock and the cfg(not(stage0)) is still there (it's not needed)

[toffaletti]

You're right, it would help if I committed my local changes.