tracing: replace future names with spawn locations in task spans

tokio/Cargo.toml

@@ -102,7 +102,7 @@ mio = { version = "0.7.3", optional = true }
 num_cpus = { version = "1.8.0", optional = true }
 parking_lot = { version = "0.11.0", optional = true } # Not in full
 slab = { version = "0.4.1", optional = true }
-tracing = { version = "0.1.16", default-features = false, features = ["std"], optional = true } # Not in full
+tracing = { version = "0.1.21", default-features = false, features = ["std"], optional = true } # Not in full
 
 [target.'cfg(unix)'.dependencies]
 libc = { version = "0.2.42", optional = true }
@@ -131,4 +131,4 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [package.metadata.playground]
-features = ["full"]
+features = ["full"]

tokio/build.rs

@@ -0,0 +1,41 @@
+use std::{env, ffi::OsString, process::Command};
+
+fn main() {
+    match rustc_minor_version() {
+        // If rustc >= 1.47.0, we can enable `track_caller`.
+        Ok(minor) if minor >= 47 => println!("cargo:rustc-cfg=tokio_track_caller"),
+        Err(e) => println!("cargo:warning=could not parse rustc version: {}", e),
+        _ => {}
+    }
+}
+
+fn rustc_minor_version() -> Result<usize, Box<dyn std::error::Error>> {
+    let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
+    let out = Command::new(rustc).arg("-V").output()?;
+    let version_str = std::str::from_utf8(&out.stdout)?;
+    let mut parts = version_str.split(' ');
+    if parts.next() != Some("rustc") {
+        return Err(format!("weird rustc version: {:?} (missing 'rustc') ", version_str).into());
+    }
+    if let Some(part) = parts.next() {
+        let mut parts = part.split('.');
+        if parts.next() != Some("1") {
+            return Err(format!(
+                "weird rustc version: {:?} (does not start with 1)",
+                version_str
+            )
+            .into());
+        }
+        if let Some(middle) = parts.next() {
+            Ok(middle.parse()?)
+        } else {
+            Err(format!("weird rustc version: {:?} (no minor version)", version_str).into())
+        }
+    } else {
+        Err(format!(
+            "weird rustc version: {:?} (missing version entirely?) ",
+            version_str,
+        )
+        .into())
+    }
+}

tokio/src/runtime/handle.rs

@@ -39,13 +39,26 @@ impl Handle {
     //     context::enter(self.clone(), f)
     // }
 
-    /// Run the provided function on an executor dedicated to blocking operations.
+    /// Run the provided function on an executor dedicated to blocking
+    /// operations.
+    #[cfg_attr(tokio_track_caller, track_caller)]
     pub(crate) fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
     where
         F: FnOnce() -> R + Send + 'static,
     {
         #[cfg(feature = "tracing")]
         let func = {
+            #[cfg(tokio_track_caller)]
+            let location = std::panic::Location::caller();
+            #[cfg(tokio_track_caller)]
+            let span = tracing::trace_span!(
+                target: "tokio::task",
+                "task",
+                kind = %"blocking",
+                function = %std::any::type_name::<F>(),
+                spawn.location = %format_args!("{}:{}:{}", location.file(), location.line(), location.column()),
+            );
+            #[cfg(not(tokio_track_caller))]
             let span = tracing::trace_span!(
                 target: "tokio::task",
                 "task",

tokio/src/runtime/mod.rs

@@ -357,11 +357,14 @@ cfg_rt! {
         /// });
         /// # }
         /// ```
+        #[cfg_attr(tokio_track_caller, track_caller)]
         pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
         where
             F: Future + Send + 'static,
             F::Output: Send + 'static,
         {
+            #[cfg(feature = "tracing")]
+            let future = crate::util::trace::task(future, "task");
             match &self.kind {
                 #[cfg(feature = "rt-multi-thread")]
                 Kind::ThreadPool(exec) => exec.spawn(future),
@@ -385,6 +388,7 @@ cfg_rt! {
         ///     println!("now running on a worker thread");
         /// });
         /// # }
+        #[cfg_attr(tokio_track_caller, track_caller)]
         pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
         where
             F: FnOnce() -> R + Send + 'static,

tokio/src/task/blocking.rs

@@ -104,6 +104,7 @@ cfg_rt_multi_thread! {
 /// # Ok(())
 /// # }
 /// ```
+#[cfg_attr(tokio_track_caller, track_caller)]
 pub fn spawn_blocking<F, R>(f: F) -> JoinHandle<R>
 where
     F: FnOnce() -> R + Send + 'static,

tokio/src/task/local.rs

@@ -190,6 +190,7 @@ cfg_rt! {
     ///     }).await;
     /// }
     /// ```
+    #[cfg_attr(tokio_track_caller, track_caller)]
     pub fn spawn_local<F>(future: F) -> JoinHandle<F::Output>
     where
         F: Future + 'static,
@@ -273,6 +274,7 @@ impl LocalSet {
     /// }
     /// ```
     /// [`spawn_local`]: fn@spawn_local
+    #[cfg_attr(tokio_track_caller, track_caller)]
     pub fn spawn_local<F>(&self, future: F) -> JoinHandle<F::Output>
     where
         F: Future + 'static,

tokio/src/task/spawn.rs

@@ -122,6 +122,7 @@ cfg_rt! {
     /// ```text
     /// error[E0391]: cycle detected when processing `main`
     /// ```
+    #[cfg_attr(tokio_track_caller, track_caller)]
     pub fn spawn<T>(task: T) -> JoinHandle<T::Output>
     where
         T: Future + Send + 'static,

tokio/src/util/trace.rs

@@ -1,47 +1,27 @@
 cfg_trace! {
     cfg_rt! {
-        use std::future::Future;
-        use std::pin::Pin;
-        use std::task::{Context, Poll};
-        use pin_project_lite::pin_project;
-
-        use tracing::Span;
-
-        pin_project! {
-            /// A future that has been instrumented with a `tracing` span.
-            #[derive(Debug, Clone)]
-            pub(crate) struct Instrumented<T> {
-                #[pin]
-                inner: T,
-                span: Span,
-            }
-        }
-
-        impl<T: Future> Future for Instrumented<T> {
-            type Output = T::Output;
-
-            fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-                let this = self.project();
-                let _enter = this.span.enter();
-                this.inner.poll(cx)
-            }
-        }
-
-        impl<T> Instrumented<T> {
-            pub(crate) fn new(inner: T, span: Span) -> Self {
-                Self { inner, span }
-            }
-        }
+        pub(crate) use tracing::instrument::Instrumented;
 
         #[inline]
+        #[cfg_attr(tokio_track_caller, track_caller)]
         pub(crate) fn task<F>(task: F, kind: &'static str) -> Instrumented<F> {
+            use tracing::instrument::Instrument;
+            #[cfg(tokio_track_caller)]
+            let location = std::panic::Location::caller();
+            #[cfg(tokio_track_caller)]
+            let span = tracing::trace_span!(
+                target: "tokio::task",
+                "task",
+                %kind,
+                spawn.location = %format_args!("{}:{}:{}", location.file(), location.line(), location.column()),
+            );
+            #[cfg(not(tokio_track_caller))]
             let span = tracing::trace_span!(
                 target: "tokio::task",
                 "task",
                 %kind,
-                future = %std::any::type_name::<F>(),
             );
-            Instrumented::new(task, span)
+            task.instrument(span)
         }
     }
 }