fix(madsim-tokio): add try_current (#224)

* add try_current

* bump madsim-tokio version to 0.2.29

madsim-tokio/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "madsim-tokio"
-version = "0.2.28"
+version = "0.2.29"
 edition = "2021"
 authors = ["Runji Wang <[email protected]>"]
 description = "The `tokio` simulator on madsim."

madsim-tokio/src/sim/runtime.rs

@@ -1,6 +1,7 @@
 use madsim::task::{AbortHandle, JoinHandle};
 use spin::Mutex;
 use std::{future::Future, io};
+use tokio::runtime::TryCurrentError;
 
 /// Builds Tokio Runtime with custom configuration values.
 pub struct Builder {}
@@ -118,10 +119,15 @@ pub struct Handle;
 
 impl Handle {
     /// Returns a handle to the current runtime.
-    pub fn current() -> Handle {
+    pub fn current() -> Self {
         Handle
     }
 
+    /// Returns a handle to the current runtime.
+    pub fn try_current() -> Result<Self, TryCurrentError> {
+        Ok(Handle)
+    }
+
     /// Enters the runtime context.
     ///
     /// FIXME: This is currently a no-op.