Bug 1039034 - Don't leak add-on interpositions at shutdown (r=bholley)

js/xpconnect/src/XPCWrappedNativeScope.cpp

@@ -27,6 +27,26 @@ XPCWrappedNativeScope* XPCWrappedNativeScope::gScopes = nullptr;
 XPCWrappedNativeScope* XPCWrappedNativeScope::gDyingScopes = nullptr;
 XPCWrappedNativeScope::InterpositionMap* XPCWrappedNativeScope::gInterpositionMap = nullptr;
 
+NS_IMPL_ISUPPORTS(XPCWrappedNativeScope::ClearInterpositionsObserver, nsIObserver)
+
+NS_IMETHODIMP
+XPCWrappedNativeScope::ClearInterpositionsObserver::Observe(nsISupports *subject,
+                                                            const char *topic,
+                                                            const char16_t *data)
+{
+    MOZ_ASSERT(strcmp(topic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0);
+
+    // The interposition map holds strong references to interpositions, which
+    // may themselves be involved in cycles. We need to drop these strong
+    // references before the cycle collector shuts down. Otherwise we'll
+    // leak. This observer always runs before CC shutdown.
+    if (gInterpositionMap)
+        delete gInterpositionMap;
+
+    nsContentUtils::UnregisterShutdownObserver(this);
+    return NS_OK;
+}
+
 static bool
 RemoteXULForbidsXBLScope(nsIPrincipal *aPrincipal, HandleObject aGlobal)
 {
@@ -671,9 +691,6 @@ XPCWrappedNativeScope::SystemIsBeingShutDown()
 
     // Now it is safe to kill all the scopes.
     KillDyingScopes();
-
-    if (gInterpositionMap)
-        delete gInterpositionMap;
 }
 
 
@@ -707,6 +724,9 @@ XPCWrappedNativeScope::SetAddonInterposition(JSAddonId *addonId,
     if (!gInterpositionMap) {
         gInterpositionMap = new InterpositionMap();
         gInterpositionMap->init();
+
+        // Make sure to clear the map at shutdown.
+        nsContentUtils::RegisterShutdownObserver(new ClearInterpositionsObserver());
     }
     if (interp) {
         return gInterpositionMap->put(addonId, interp);

js/xpconnect/src/xpcprivate.h

@@ -110,6 +110,7 @@
 #include "nsIInterfaceInfo.h"
 #include "nsIXPCScriptable.h"
 #include "nsIJSRuntimeService.h"
+#include "nsIObserver.h"
 #include "nsWeakReference.h"
 #include "nsCOMPtr.h"
 #include "nsXPTCUtils.h"
@@ -1176,6 +1177,14 @@ protected:
     XPCWrappedNativeScope(); // not implemented
 
 private:
+    class ClearInterpositionsObserver MOZ_FINAL : public nsIObserver {
+        ~ClearInterpositionsObserver() {}
+
+      public:
+        NS_DECL_ISUPPORTS
+        NS_DECL_NSIOBSERVER
+    };
+
     static XPCWrappedNativeScope* gScopes;
     static XPCWrappedNativeScope* gDyingScopes;