safety: ensure RMain exists before checking busy state

crates/ark/src/interface.rs

@@ -293,7 +293,7 @@ pub struct RMain {
 
     dap: Arc<Mutex<Dap>>,
     is_debugging: bool,
-    
+
     /// Whether or not R itself is actively busy.
     /// This does not represent the busy state of the kernel.
     pub is_busy: bool,
@@ -408,6 +408,16 @@ impl RMain {
         RMain::get_mut()
     }
 
+    /// Indicate whether RMain has been created and is initialized.
+    pub fn initialized() -> bool {
+        unsafe {
+            match &R_MAIN {
+                Some(main) => !main.initializing,
+                None => false,
+            }
+        }
+    }
+
     /// Access a mutable reference to the singleton instance of this struct
     ///
     /// SAFETY: Accesses must occur after `start_r()` initializes it, and must

crates/ark/src/kernel.rs

@@ -1,7 +1,7 @@
 //
 // kernel.rs
 //
-// Copyright (C) 2022 Posit Software, PBC. All rights reserved.
+// Copyright (C) 2023 Posit Software, PBC. All rights reserved.
 //
 //
 
@@ -73,8 +73,11 @@ impl Kernel {
 
         // Get the current busy status
         let busy = r_task(|| {
-            let main = RMain::get();
-            main.is_busy
+            if RMain::initialized() {
+                RMain::get().is_busy
+            } else {
+                false
+            }
         });
         self.send_event(PositronEvent::Busy(BusyEvent { busy }));
     }