This breaks a fair amount of code. The typical patterns are:
* `for _ in range(0, 10)`: change to `for _ in range(0u, 10)`;
* `println!("{}", 3)`: change to `println!("{}", 3i)`;
* `[1, 2, 3].len()`: change to `[1i, 2, 3].len()`.
RFC #30. Closes#6023.
[breaking-change]
This commit is the final step in the libstd facade, #13851. The purpose of this
commit is to move libsync underneath the standard library, behind the facade.
This will allow core primitives like channels, queues, and atomics to all live
in the same location.
There were a few notable changes and a few breaking changes as part of this
movement:
* The `Vec` and `String` types are reexported at the top level of libcollections
* The `unreachable!()` macro was copied to libcore
* The `std::rt::thread` module was moved to librustrt, but it is still
reexported at the same location.
* The `std::comm` module was moved to libsync
* The `sync::comm` module was moved under `sync::comm`, and renamed to `duplex`.
It is now a private module with types/functions being reexported under
`sync::comm`. This is a breaking change for any existing users of duplex
streams.
* All concurrent queues/deques were moved directly under libsync. They are also
all marked with #![experimental] for now if they are public.
* The `task_pool` and `future` modules no longer live in libsync, but rather
live under `std::sync`. They will forever live at this location, but they may
move to libsync if the `std::task` module moves as well.
[breaking-change]
Optimize `Once::doit`: perform optimistic check that initializtion is
already completed. `load` is much cheaper than `fetch_add` at least
on x86_64.
Verified with this test:
```
static mut o: one::Once = one::ONCE_INIT;
unsafe {
loop {
let start = time::precise_time_ns();
let iters = 50000000u64;
for _ in range(0, iters) {
o.doit(|| { println!("once!"); });
}
let end = time::precise_time_ns();
let ps_per_iter = 1000 * (end - start) / iters;
println!("{} ps per iter", ps_per_iter);
// confuse the optimizer
o.doit(|| { println!("once!"); });
}
}
```
Test executed on Mac, Intel Core i7 2GHz. Result is:
* 20ns per iteration without patch
* 4ns per iteration with this patch applied
Once.doit could be even faster (800ps per iteration), if `doit` function
was split into a pair of `doit`/`doit_slow`, and `doit` marked as
`#[inline]` like this:
```
#[inline(always)]
pub fn doit(&self, f: ||) {
if self.cnt.load(atomics::SeqCst) < 0 {
return
}
self.doit_slow(f);
}
fn doit_slow(&self, f: ||) { ... }
```
Similarly to the rest of the previous commits, this moves the once primitive to
using &self instead of &mut self for proper sharing among many threads now.
