rt: `worker_threads` must be non-zero (#2947)

Co-authored-by: Alice Ryhl <alice@ryhl.io>

1 files changed, 5 insertions, 0 deletions

diff --git a/tokio/src/runtime/builder.rs b/tokio/src/runtime/builder.rs
index f260eac6..27981d33 100644
--- a/tokio/src/runtime/builder.rs
+++ b/tokio/src/runtime/builder.rs
@@ -192,7 +192,12 @@ impl Builder {
     /// // This will run the runtime and future on the current thread
     /// rt.block_on(async move {});
     /// ```
+    ///
+    /// # Panic
+    ///
+    /// This will panic if `val` is not larger than `0`.
     pub fn worker_threads(&mut self, val: usize) -> &mut Self {
+        assert!(val > 0, "Worker threads cannot be set to 0");
         self.worker_threads = Some(val);
         self
     }