Rename lib to binstalk (#361)

crates/binstalk/src/helpers/jobserver_client.rs

@@ -0,0 +1,33 @@
+use std::{num::NonZeroUsize, sync::Arc, thread::available_parallelism};
+
+use jobslot::Client;
+use tokio::sync::OnceCell;
+
+use crate::errors::BinstallError;
+
+#[derive(Clone)]
+pub struct LazyJobserverClient(Arc<OnceCell<Client>>);
+
+impl LazyJobserverClient {
+    /// This must be called at the start of the program since
+    /// `Client::from_env` requires that.
+    #[allow(clippy::new_without_default)]
+    pub fn new() -> Self {
+        // Safety:
+        //
+        // Client::from_env is unsafe because from_raw_fd is unsafe.
+        // It doesn't do anything that is actually unsafe, like
+        // dereferencing pointer.
+        let opt = unsafe { Client::from_env() };
+        Self(Arc::new(OnceCell::new_with(opt)))
+    }
+
+    pub async fn get(&self) -> Result<&Client, BinstallError> {
+        self.0
+            .get_or_try_init(|| async {
+                let ncore = available_parallelism().map(NonZeroUsize::get).unwrap_or(1);
+                Ok(Client::new(ncore)?)
+            })
+            .await
+    }
+}