cargo build -j <large> does not start compiling

[matthiaskrgr]

Problem

.

Steps

1. go into cargo repo
2. cargo build -j 100000
3. observe as cargo neither consumes any CPU nor starts actually compiling 🤔

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.69.0-nightly (39c13e67a 2023-02-12)
release: 1.69.0-nightly
commit-hash: 39c13e67a5962466cc7253d41bc1099bbcb224c3
commit-date: 2023-02-12
host: x86_64-unknown-linux-gnu
libgit2: 1.5.0 (sys:0.16.0 vendored)
libcurl: 7.86.0-DEV (sys:0.4.59+curl-7.86.0 vendored ssl:OpenSSL/1.1.1q)
os: Manjaro 22.0.3 (Sikaris) [64-bit]

[matthiaskrgr]

with CARGO_LOG=debug cargo

        ): {
            "clone-impls",
            "default",
            "derive",
            "full",
            "parsing",
            "printing",
            "proc-macro",
            "quote",
        },
        (
            PackageId {
                name: "sha2",
                version: "0.10.6",
                source: "registry `crates-io`",
            },
            NormalOrDev,
        ): {
            "default",
            "std",
        },
    }
[2023-02-15T21:43:20Z DEBUG cargo::util::rustc] adding rustup info to rustc fingerprint
[2023-02-15T21:43:20Z DEBUG cargo::util::rustc] reusing existing rustc info cache
[2023-02-15T21:43:20Z DEBUG cargo::util::rustc] rustc info cache hit

[ehuss]

This is likely the jobserver filling the pipe beyond pipe-max-size (which I think is 64k on most linux systems?).

[matthiaskrgr]

Oh interesting.
It indeed breaks at around 67000 but works with 64000. Guess I will never use my system to its true potential 🙃

I checked with strace and I saw a bunch of

write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1
write(30, "|", 1)                       = 1

Ceci n'est pas une pipe :)