rt: forward panic_handler to tokio::runtime::Builder (#1055)

tokio/src/runtime/threadpool/builder.rs

@@ -5,6 +5,7 @@ use reactor::Reactor;
 use std::io;
 use std::sync::Mutex;
 use std::time::Duration;
+use std::any::Any;
 
 use num_cpus;
 use tokio_reactor;
@@ -101,6 +102,37 @@ impl Builder {
         self
     }
 
+    /// Sets a callback to handle panics in futures.
+    ///
+    /// The callback is triggered when a panic during a future bubbles up to
+    /// Tokio. By default Tokio catches these panics, and they will be ignored.
+    /// The parameter passed to this callback is the same error value returned
+    /// from `std::panic::catch_unwind()`. To abort the process on panics, use
+    /// `std::panic::resume_unwind()` in this callback as shown below.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # extern crate tokio;
+    /// # extern crate futures;
+    /// # use tokio::runtime;
+    ///
+    /// # pub fn main() {
+    /// let mut rt = runtime::Builder::new()
+    ///     .panic_handler(|err| std::panic::resume_unwind(err))
+    ///     .build()
+    ///     .unwrap();
+    /// # }
+    /// ```
+    pub fn panic_handler<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn(Box<Any + Send>) + Send + Sync + 'static,
+    {
+        self.threadpool_builder.panic_handler(f);
+        self
+    }
+
+
     /// Set the maximum number of worker threads for the `Runtime`'s thread pool.
     ///
     /// This must be a number between 1 and 32,768 though it is advised to keep