crates/iceberg/src/utils.rs

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//   http://www.apache.org/licenses/LICENSE-2.0
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use std::num::NonZeroUsize;

// Use a default value of 1 as the safest option.
// See https://doc.rust-lang.org/std/thread/fn.available_parallelism.html#limitations
// for more details.
const DEFAULT_PARALLELISM: usize = 1;

/// Uses [`std::thread::available_parallelism`] in order to
/// retrieve an estimate of the default amount of parallelism
/// that should be used. Note that [`std::thread::available_parallelism`]
/// returns a `Result` as it can fail, so here we use
/// a default value instead.
/// Note: we don't use a OnceCell or LazyCell here as there
/// are circumstances where the level of available
/// parallelism can change during the lifetime of an executing
/// process, but this should not be called in a hot loop.
pub(crate) fn available_parallelism() -> NonZeroUsize {
    std::thread::available_parallelism().unwrap_or_else(|_err| {
        // Failed to get the level of parallelism.
        // TODO: log/trace when this fallback occurs.

        // Using a default value.
        NonZeroUsize::new(DEFAULT_PARALLELISM).unwrap()
    })
}