deprecation warning in nix on OSX

[oconnor663]

https://travis-ci.org/oconnor663/os_pipe.rs/jobs/408710890

warning: use of deprecated item 'sys::nix::unistd::pipe2': pipe2(2) is not actually atomic on these platforms.  Use pipe(2) and fcntl(2) instead
  --> src/unix.rs:17:9
   |
17 |         nix::unistd::pipe2(nix::fcntl::OFlag::O_CLOEXEC).map_err(nix_err_to_io_err)?;
   |         ^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(deprecated)] on by default

[oconnor663]

Related to nix-rust/nix#777.

[oconnor663]

rust-lang/rust#24237
https://www.python.org/dev/peps/pep-0433

[zopsicle]

This crate no longer depends on the nix crate (since 68c8bf5), so I think this issue can be closed.

[parasyte]

Though it's true that the nix dependency is gone, there is still an open question WRT macOS. namely this comment:

os_pipe.rs/src/unix.rs

Lines 9 to 13 in a4ff43d

	// We need to atomically create pipes and set the CLOEXEC flag on them. This is
	// done with the pipe2() API. However, macOS doesn't support pipe2. There, all
	// we can do is call pipe() followed by fcntl(), and hope that no other threads
	// fork() in between. The following code is copied from the nix crate, where it
	// works but is deprecated.

It's probably good that some issue remains open while "hope that no other threads fork()" is a concern.

[oconnor663]

My understanding is that there's simply no way to accomplish this on macOS. (I assume the same fundamental issue affects std::process::Command.) And of course if pipe2 or similar is ever added, there will be a long tail of backwards compatibility headaches related to using it. But if I'm wrong about either of those things I'd love to know.

[NobodyXu]

cc copies the code from stdlib for pipe creation and it simply uses pipe on MacOS

https://github.com/rust-lang/cc-rs/blob/daab9244b03e244c4f2511944870d719c443f61f/src/os_pipe/unix.rs#L11