cc 1.0.42 with "parallel" feature hangs on Windows

[Vlad-Shcherbina]

To reproduce

1. cargo new --bin сс_jobserver
cd cc_jobserver
2. In Cargo.toml, put the following:

   [dependencies]
   rusqlite = { version = "*", features = ["bundled"] }
   zstd = { version = "*", default-features = false }
   

   (my Cargo.lock if you want to reproduce perfectly)
3. cargo build

Expected result

Build completes in finite time.

Actual result

The build hangs in the following state:

> cargo build
    Updating crates.io index
   Compiling log v0.4.8
   Compiling getrandom v0.1.12
   Compiling jobserver v0.1.17
   Compiling cc v1.0.42
   Compiling zstd-sys v1.4.13+zstd.1.4.3
   Compiling libsqlite3-sys v0.16.0
    Building [============================================>            ] 32/40: zstd-sys(build), libsqlite3-sys(bu...

The process tree looks like this:

These two build-script-build.exe don't use CPU and don't make any progress.

---

I think this is related to cc 1.0.42 because first, if I pin cc to 1.0.41, it builds successfully, and second, because there was this change: 4fda8db .

---

Version info:

> cargo --version --verbose
cargo 1.39.0-nightly (3f700ec43 2019-08-19)
release: 1.39.0
commit-hash: 3f700ec43ce72305eb5315cfc710681f3469d4b4
commit-date: 2019-08-19

rustc --version --verbose
rustc 1.39.0-nightly (521d78407 2019-08-25)
binary: rustc
commit-hash: 521d78407471cb78e9bbf47160f6aa23047ac499
commit-date: 2019-08-25
host: x86_64-pc-windows-msvc
release: 1.39.0-nightly
LLVM version: 9.0

I observe this problem on a machine with 2 cores.

[alexcrichton]

Oops sorry about that! Should be fixed in 238ee4f

[Vlad-Shcherbina]

Thank you. I confirm it appears to work fine with cc 1.0.45.