add System::try_current (#275)

actix-rt/CHANGES.md

@@ -2,8 +2,10 @@
 
 ## Unreleased - 2021-xx-xx
 * Add `Arbiter::handle` to get a handle of an owned Arbiter. [#274]
+* Add `System::try_current` for situations where actix may or may not be running a System. [#275]
 
 [#274]: https://github.com/actix/actix-net/pull/274
+[#275]: https://github.com/actix/actix-net/pull/275
 
 
 ## 2.0.1 - 2021-02-06

actix-rt/src/system.rs

@@ -100,6 +100,15 @@ impl System {
         })
     }
 
+    /// Try to get current running system.
+    ///
+    /// Returns `None` if no System has been started.
+    ///
+    /// Contrary to `current`, this never panics.
+    pub fn try_current() -> Option<System> {
+        CURRENT.with(|cell| cell.borrow().clone())
+    }
+
     /// Get handle to a the System's initial [Arbiter].
     pub fn arbiter(&self) -> &ArbiterHandle {
         &self.arbiter_handle

actix-rt/tests/tests.rs

@@ -288,3 +288,13 @@ fn new_arbiter_with_tokio() {
 
     assert_eq!(false, counter.load(Ordering::SeqCst));
 }
+
+#[test]
+fn try_current_no_system() {
+    assert!(System::try_current().is_none())
+}
+
+#[test]
+fn try_current_with_system() {
+    System::new().block_on(async { assert!(System::try_current().is_some()) });
+}