From 571d01cb73c22e6b7bc645b4e59f0b06d85f7d0f Mon Sep 17 00:00:00 2001 From: Hayden Stainsby Date: Sat, 18 Nov 2023 18:56:35 +0100 Subject: [PATCH] task: make task span explicit root In Tokio, tasks are optionally instrumented with tracing spans to allow analysis of the runtime behavior to be performed with tools like tokio-console. The span that is created for each task gets currently follows the default tracing behavior and has a contextual parent attached to it based on the span that is actual when `tokio::spawn` or similar is called. However, in tracing, a span will remain "alive" until all its children spans are closed. This doesn't match how spawned tasks work. A task may outlive the context in which is was spawned (and frequently does). This causes tasks which spawn other - longer living - tasks to appear in `tokio-console` as having lost their waker when instead they should be shown as completed (tokio-rs/console#345). It can also cause undesired behavior for unrelated tracing spans if a subscriber is receiving both the other spans as well as Tokio's instrumentation. To fix this mismatch in behavior, the task span has `parent: None` set on it, making it an explicit root - it has no parent. The same was already done for all spans representing resources in #6107. This change is made within the scope of #5792. Due to a defect in the currently available `tracing-mock` crate, it is not possible to test this change at a tracing level (tokio-rs/tracing#2440). Instead, a test for the `console-subscriber` has been written which shows that this change fixes the defect as observed in `tokio-console` (tokio-rs/console#490). --- tokio/src/util/trace.rs | 1 + 1 file changed, 1 insertion(+) diff --git a/tokio/src/util/trace.rs b/tokio/src/util/trace.rs index be5602dcba3..e1827686ca9 100644 --- a/tokio/src/util/trace.rs +++ b/tokio/src/util/trace.rs @@ -16,6 +16,7 @@ cfg_trace! { let location = std::panic::Location::caller(); tracing::trace_span!( target: "tokio::task", + parent: None, "runtime.spawn", %kind, task.name = %name.unwrap_or_default(),