tokio: don't panic if taskdump request is cancelled

ref: tokio-rs#5717 (comment)

Author: jswrenn

examples/dump.rs

@@ -45,7 +45,6 @@ async fn main() {
         _ = tokio::spawn(c()) => {},
         _ = dump() => {},
     );
-
 }
 
 #[cfg(not(all(

tokio/src/runtime/handle.rs

@@ -346,7 +346,7 @@ cfg_taskdump! {
                 scheduler::Handle::CurrentThread(handle) => handle.dump(),
                 #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
                 scheduler::Handle::MultiThread(handle) => {
-                    // perform the trace in a separate thread so that the 
+                    // perform the trace in a separate thread so that the
                     // trace itself does not appear in the taskdump.
                     let handle = handle.clone();
                     spawn_thread(|| {
@@ -366,9 +366,7 @@ cfg_taskdump! {
     {
         let (tx, rx) = crate::sync::oneshot::channel();
         crate::loom::thread::spawn(|| {
-            if tx.send(f()).is_err() {
-                unreachable!("send failed");
-            }
+            let _ = tx.send(f());
         });
         rx.await.unwrap()
     }

tokio/src/runtime/scheduler/multi_thread/worker.rs

@@ -908,11 +908,7 @@ impl Core {
 
         if !self.is_traced {
             // Check if the worker should be tracing.
-            self.is_traced = worker
-                .handle
-                .shared
-                .trace_status
-                .trace_requested();
+            self.is_traced = worker.handle.shared.trace_status.trace_requested();
         }
     }
 
@@ -1095,7 +1091,7 @@ impl Handle {
         }
     }
 
-    cfg_taskdump!{
+    cfg_taskdump! {
         fn trace_core(&self, mut core: Box<Core>) -> Box<Core> {
             use crate::runtime::dump;
             use task::trace::trace_multi_thread;

tokio/src/runtime/task/trace/mod.rs

@@ -290,7 +290,6 @@ pub(in crate::runtime) fn trace_multi_thread(
         let ((), trace) = Trace::capture(|| task.as_raw().poll());
         traces.push(trace);
 
-
         // reschedule the task
         let _ = task.as_raw().state().transition_to_notified_by_ref();
         task.as_raw().schedule();

tokio/tests/dump.rs

@@ -57,7 +57,7 @@ fn current_thread() {
             _ = tokio::spawn(a()) => {},
             _ = tokio::spawn(a()) => {},
             _ = dump() => {},
-        );        
+        );
     });
 }
 
@@ -93,6 +93,6 @@ fn multi_thread() {
             _ = tokio::spawn(a()) => {},
             _ = tokio::spawn(a()) => {},
             _ = dump() => {},
-        );        
+        );
     });
 }