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Matthias Krüger
2dd2fb728e
available_parallelism: Gracefully handle zero value cfs_period_us There seem to be some scenarios where the cgroup cpu quota field `cpu.cfs_period_us` can contain `0`. This field is used to determine the "amount" of parallelism suggested by the function `std::thread::available_parallelism` A zero value of this field cause a panic when `available_parallelism()` is invoked. This issue was detected by the call from binaries built by `cargo test`. I really don't feel like `0` is a good value for `cpu.cfs_period_us`, but I also don't think applications should panic if this value is seen. This panic started happening with rust 1.64.0. This case is gracefully handled by other projects which read this information: [num_cpus](https://github.com/seanmonstar/num_cpus/blob/e437b9d9083d717692e35d917de8674a7987dd06/src/linux.rs#L207-L210), [ninja](https://github.com/ninja-build/ninja/pull/2174/files), [dotnet](https://github.com/dotnet/runtime/blob/c4341d45acca3ea662cd8d71e7d71094450dd045/src/coreclr/pal/src/misc/cgroup.cpp#L481-L483) Before this change, running `cargo test` in environments configured as described above would trigger this panic: ``` $ RUST_BACKTRACE=1 cargo test Finished test [unoptimized + debuginfo] target(s) in 3.55s Running unittests src/main.rs (target/debug/deps/x-9a42e145aca2934d) thread 'main' panicked at 'attempt to divide by zero', library/std/src/sys/unix/thread.rs:546:70 stack backtrace: 0: rust_begin_unwind 1: core::panicking::panic_fmt 2: core::panicking::panic 3: std::sys::unix::thread::cgroups::quota 4: std::sys::unix::thread::available_parallelism 5: std::thread::available_parallelism 6: test::helpers::concurrency::get_concurrency 7: test::console::run_tests_console 8: test::test_main 9: test::test_main_static 10: x::main at ./src/main.rs:1:1 11: core::ops::function::FnOnce::call_once at /tmp/rust-1.64-1.64.0-1/library/core/src/ops/function.rs:248:5 note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. error: test failed, to rerun pass '--bin x' ``` I've tested this change in an environment which has the bad (questionable?) setup and rebuilding the test executable against a fixed std library fixes the panic.