actix-rt: Add Arbiter::is_running helper and fix System::is_set doc

`Arbiter::is_running` can be used to check if the current even-loop is currently
running; which should also work after the system has stopped. `System::is_set`
was updated to reflect what it actually does, it tells if the event loop has
started, which alone can't tell if it has stopped.

Signed-off-by: Jonathas-Conceicao <jadoliveira@inf.ufpel.edu.br>

actix-rt/src/arbiter.rs

@@ -89,6 +89,11 @@ impl Arbiter {
         })
     }
 
+    /// Check if current arbiter is running.
+    pub fn is_running() -> bool {
+        RUNNING.with(|cell| cell.get())
+    }
+
     /// Stop arbiter from continuing it's event loop.
     pub fn stop(&self) {
         let _ = self.sender.unbounded_send(ArbiterCommand::Stop);

actix-rt/src/system.rs

@@ -79,7 +79,7 @@ impl System {
         })
     }
 
-    /// Check if current system is running.
+    /// Check if current system is set, i.e., as already been started.
     pub fn is_set() -> bool {
         CURRENT.with(|cell| cell.borrow().is_some())
     }