Bug 1861252 - Anticipate servo thread pool shutdown in leak checking builds. r=xpcom-reviewers,emilio

Differential Revision: https://phabricator.services.mozilla.com/D195098

xpcom/build/XPCOMInit.cpp

@@ -635,6 +635,13 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
       observerService->Shutdown();
     }
 
+#ifdef NS_FREE_PERMANENT_DATA
+    // In leak-checking / ASAN / etc. builds, shut down the Servo thread-pool,
+    // which will wait for all the work to be done. For other builds, we don't
+    // really want to wait on shutdown for possibly slow tasks.
+    Servo_ShutdownThreadPool();
+#endif
+
     // XPCOMShutdownFinal is the default phase for ClearOnShutdown.
     // This AdvanceShutdownPhase will thus free most ClearOnShutdown()'ed
     // smart pointers. Some destructors may fire extra main thread runnables
@@ -768,16 +775,10 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
   GkRust_Shutdown();
 
 #ifdef NS_FREE_PERMANENT_DATA
-  // By the time we're shutting down, there may still be async parse tasks going
-  // on in the Servo thread-pool. This is fairly uncommon, though not
-  // impossible. CSS parsing heavily uses the atom table, so obviously it's not
-  // fine to get rid of it.
-  //
-  // In leak-checking / ASAN / etc. builds, shut down the servo thread-pool,
-  // which will wait for all the work to be done. For other builds, we don't
-  // really want to wait on shutdown for possibly slow tasks. So just leak the
-  // atom table in those.
-  Servo_ShutdownThreadPool();
+  // As we do shutdown Servo only in leak-checking builds, there may still
+  // be async parse tasks going on in the Servo thread-pool in other builds.
+  // CSS parsing heavily uses the atom table, so we can safely drop it only
+  // if Servo has been stopped, too.
   NS_ShutdownAtomTable();
 #endif