Bug 966762 - Add chrome JS function to unlink ghost windows. r=smaug

dom/base/nsGlobalWindow.cpp

@@ -1809,6 +1809,14 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsGlobalWindow)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mCrypto)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
+#ifdef DEBUG
+void
+nsGlobalWindow::RiskyUnlink()
+{
+  NS_CYCLE_COLLECTION_INNERNAME.Unlink(this);
+}
+#endif
+
 struct TraceData
 {
   const TraceCallbacks& callbacks;

dom/base/nsGlobalWindow.h

@@ -604,6 +604,12 @@ public:
   NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsGlobalWindow,
                                                                    nsIDOMEventTarget)
 
+#ifdef DEBUG
+  // Call Unlink on this window. This may cause bad things to happen, so use
+  // with caution.
+  void RiskyUnlink();
+#endif
+
   virtual NS_HIDDEN_(JSObject*)
     GetCachedXBLPrototypeHandler(nsXBLPrototypeHandler* aKey);
 

dom/base/nsWindowMemoryReporter.cpp

@@ -836,3 +836,45 @@ nsWindowMemoryReporter::GhostWindowsReporter::DistinguishedAmount()
   return ghostWindows.Count();
 }
 
+#ifdef DEBUG
+static PLDHashOperator
+UnlinkGhostWindowsEnumerator(nsUint64HashKey* aIDHashKey, void *)
+{
+  nsGlobalWindow::WindowByIdTable* windowsById =
+    nsGlobalWindow::GetWindowsTable();
+  if (!windowsById) {
+    return PL_DHASH_NEXT;
+  }
+
+  nsRefPtr<nsGlobalWindow> window = windowsById->Get(aIDHashKey->GetKey());
+  if (window) {
+    window->RiskyUnlink();
+  }
+
+  return PL_DHASH_NEXT;
+}
+
+/* static */ void
+nsWindowMemoryReporter::UnlinkGhostWindows()
+{
+  if (!sWindowReporter) {
+    return;
+  }
+
+  nsGlobalWindow::WindowByIdTable* windowsById =
+    nsGlobalWindow::GetWindowsTable();
+  if (!windowsById) {
+    return;
+  }
+
+  // Hold on to every window in memory so that window objects can't be
+  // destroyed while we're calling the UnlinkGhostWindows callback.
+  WindowArray windows;
+  windowsById->Enumerate(GetWindows, &windows);
+
+  // Get the IDs of all the "ghost" windows, and unlink them all.
+  nsTHashtable<nsUint64HashKey> ghostWindows;
+  sWindowReporter->CheckForGhostWindows(&ghostWindows);
+  ghostWindows.EnumerateEntries(UnlinkGhostWindowsEnumerator, nullptr);
+}
+#endif

dom/base/nsWindowMemoryReporter.h

@@ -146,6 +146,14 @@ public:
 
   static void Init();
 
+#ifdef DEBUG
+  /**
+   * Unlink all known ghost windows, to enable investigating what caused them
+   * to become ghost windows in the first place.
+   */
+  static void UnlinkGhostWindows();
+#endif
+
 private:
   /**
    * nsGhostWindowReporter generates the "ghost-windows" report, which counts

js/xpconnect/idl/xpccomponents.idl

@@ -121,7 +121,7 @@ interface ScheduledGCCallback : nsISupports
 /**
 * interface of Components.utils
 */
-[scriptable, uuid(f4b12240-02aa-47e5-99d5-43cd50fbd4b7)]
+[scriptable, uuid(0b81b4f2-cad7-4602-a5cb-b99c9d514196)]
 interface nsIXPCComponents_Utils : nsISupports
 {
 
@@ -279,6 +279,12 @@ interface nsIXPCComponents_Utils : nsISupports
      */
     void schedulePreciseShrinkingGC(in ScheduledGCCallback callback);
 
+    /*
+     * In a debug build, unlink any ghost windows. This is only for debugging
+     * leaks, and can cause bad things to happen if called.
+     */
+    void unlinkGhostWindows();
+
     /**
      * Return the keys in a weak map.  This operation is
      * non-deterministic because it is affected by the scheduling of the

js/xpconnect/src/XPCComponents.cpp

@@ -2857,6 +2857,18 @@ nsXPCComponents_Utils::SchedulePreciseShrinkingGC(ScheduledGCCallback* aCallback
     return NS_DispatchToMainThread(event);
 }
 
+/* void unlinkGhostWindows(); */
+NS_IMETHODIMP
+nsXPCComponents_Utils::UnlinkGhostWindows()
+{
+#ifdef DEBUG
+    nsWindowMemoryReporter::UnlinkGhostWindows();
+    return NS_OK;
+#else
+    return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
 /* [implicit_jscontext] jsval nondeterministicGetWeakMapKeys(in jsval aMap); */
 NS_IMETHODIMP
 nsXPCComponents_Utils::NondeterministicGetWeakMapKeys(HandleValue aMap,