rt: add runtime Id

tokio/src/runtime/handle.rs

@@ -1,3 +1,5 @@
+#[cfg(tokio_unstable)]
+use crate::runtime;
 use crate::runtime::{context, scheduler, RuntimeFlavor};
 
 /// Handle to the runtime.
@@ -357,6 +359,35 @@ impl Handle {
             scheduler::Handle::MultiThread(_) => RuntimeFlavor::MultiThread,
         }
     }
+
+    cfg_unstable! {
+        /// Returns the [`Id`] of the current `Runtime`.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Handle;
+        ///
+        /// #[tokio::main(flavor = "current_thread")]
+        /// async fn main() {
+        ///   println!("Current runtime id: {}", Handle::current().id());
+        /// }
+        /// ```
+        ///
+        /// **Note**: This is an [unstable API][unstable]. The public API of this type
+        /// may break in 1.x releases. See [the documentation on unstable
+        /// features][unstable] for details.
+        ///
+        /// [unstable]: crate#unstable-features
+        /// [`Id`]: struct@crate::runtime::Id
+        pub fn id(&self) -> runtime::Id {
+            match &self.inner {
+                scheduler::Handle::CurrentThread(handle) => handle.runtime_id,
+                #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
+                scheduler::Handle::MultiThread(handle) => handle.runtime_id,
+            }
+        }
+    }
 }
 
 cfg_metrics! {

tokio/src/runtime/id.rs

@@ -0,0 +1,49 @@
+use std::fmt;
+
+/// An opaque ID that uniquely identifies a runtime relative to all other currently
+/// running runtimes.
+///
+/// # Notes
+///
+/// - Runtime IDs are unique relative to other *currently running* runtimes.
+///   When a task completes, the same ID may be used for another task.
+/// - Runtime IDs are *not* sequential, and do not indicate the order in which
+///   runtimes are started or any other data.
+/// - The runtime ID of the currently running task can be obtained from the
+///   Handle.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::runtime::Handle;
+///
+/// #[tokio::main(flavor = "multi_thread", worker_threads = 4)]
+/// async fn main() {
+///   println!("Current runtime id: {}", Handle::current().id());
+/// }
+/// ```
+///
+/// **Note**: This is an [unstable API][unstable]. The public API of this type
+/// may break in 1.x releases. See [the documentation on unstable
+/// features][unstable] for details.
+///
+/// [unstable]: crate#unstable-features
+#[cfg_attr(not(tokio_unstable), allow(unreachable_pub))]
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+pub struct Id(u64);
+
+impl fmt::Display for Id {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl Id {
+    pub(crate) fn next() -> Self {
+        use crate::loom::sync::atomic::{Ordering::Relaxed, StaticAtomicU64};
+
+        static NEXT_ID: StaticAtomicU64 = StaticAtomicU64::new(1);
+
+        Self(NEXT_ID.fetch_add(1, Relaxed))
+    }
+}

tokio/src/runtime/mod.rs

@@ -226,6 +226,10 @@ cfg_rt! {
     mod builder;
     pub use self::builder::Builder;
     cfg_unstable! {
+        mod id;
+        #[cfg_attr(not(tokio_unstable), allow(unreachable_pub))]
+        pub use id::Id;
+
         pub use self::builder::UnhandledPanic;
         pub use crate::util::rand::RngSeed;
     }

tokio/src/runtime/scheduler/current_thread.rs

@@ -1,6 +1,8 @@
 use crate::future::poll_fn;
 use crate::loom::sync::atomic::AtomicBool;
 use crate::loom::sync::Arc;
+#[cfg(tokio_unstable)]
+use crate::runtime;
 use crate::runtime::driver::{self, Driver};
 use crate::runtime::scheduler::{self, Defer, Inject};
 use crate::runtime::task::{self, JoinHandle, OwnedTasks, Schedule, Task};
@@ -41,6 +43,9 @@ pub(crate) struct Handle {
 
     /// Current random number generator seed
     pub(crate) seed_generator: RngSeedGenerator,
+
+    #[cfg(tokio_unstable)]
+    pub(crate) runtime_id: runtime::Id,
 }
 
 /// Data required for executing the scheduler. The struct is passed around to
@@ -141,6 +146,8 @@ impl CurrentThread {
             driver: driver_handle,
             blocking_spawner,
             seed_generator,
+            #[cfg(tokio_unstable)]
+            runtime_id: runtime::Id::next(),
         });
 
         let core = AtomicCell::new(Some(Box::new(Core {

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

@@ -1,5 +1,7 @@
 use crate::future::Future;
 use crate::loom::sync::Arc;
+#[cfg(tokio_unstable)]
+use crate::runtime;
 use crate::runtime::scheduler::multi_thread::worker;
 use crate::runtime::{
     blocking, driver,
@@ -30,6 +32,9 @@ pub(crate) struct Handle {
 
     /// Current random number generator seed
     pub(crate) seed_generator: RngSeedGenerator,
+
+    #[cfg(tokio_unstable)]
+    pub(crate) runtime_id: runtime::Id,
 }
 
 impl Handle {

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

@@ -302,6 +302,8 @@ pub(super) fn create(
         driver: driver_handle,
         blocking_spawner,
         seed_generator,
+        #[cfg(tokio_unstable)]
+        runtime_id: runtime::Id::next(),
     });
 
     let mut launch = Launch(vec![]);

tokio/tests/rt_handle.rs

@@ -60,6 +60,29 @@ fn interleave_then_enter() {
     let _enter = rt3.enter();
 }
 
+#[cfg(tokio_unstable)]
+mod unstable {
+    use super::*;
+
+    #[test]
+    fn runtime_id_is_same() {
+        let rt = rt();
+
+        let handle1 = rt.handle();
+        let handle2 = rt.handle();
+
+        assert_eq!(handle1.id(), handle2.id());
+    }
+
+    #[test]
+    fn runtime_ids_different() {
+        let rt1 = rt();
+        let rt2 = rt();
+
+        assert_ne!(rt1.handle().id(), rt2.handle().id());
+    }
+}
+
 fn rt() -> Runtime {
     tokio::runtime::Builder::new_current_thread()
         .build()

tokio/tests/rt_threaded.rs

@@ -762,4 +762,22 @@ mod unstable {
             .unwrap();
         })
     }
+
+    #[test]
+    fn runtime_id_is_same() {
+        let rt = rt();
+
+        let handle1 = rt.handle();
+        let handle2 = rt.handle();
+
+        assert_eq!(handle1.id(), handle2.id());
+    }
+
+    #[test]
+    fn runtime_ids_different() {
+        let rt1 = rt();
+        let rt2 = rt();
+
+        assert_ne!(rt1.handle().id(), rt2.handle().id());
+    }
 }