diff -r 000000000000 -r 6474c204b198 xpcom/glue/nsCategoryCache.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/nsCategoryCache.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,95 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsCategoryCache_h_
+#define nsCategoryCache_h_
+
+#include "mozilla/Attributes.h"
+
+#include "nsICategoryManager.h"
+#include "nsIObserver.h"
+#include "nsISimpleEnumerator.h"
+#include "nsISupportsPrimitives.h"
+
+#include "nsServiceManagerUtils.h"
+
+#include "nsAutoPtr.h"
+#include "nsCOMArray.h"
+#include "nsInterfaceHashtable.h"
+
+#include "nsXPCOM.h"
+
+class NS_COM_GLUE nsCategoryObserver MOZ_FINAL : public nsIObserver
+{
+  public:
+    nsCategoryObserver(const char* aCategory);
+    ~nsCategoryObserver();
+
+    void ListenerDied();
+    nsInterfaceHashtable<nsCStringHashKey, nsISupports>& GetHash()
+    {
+      return mHash;
+    }
+
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIOBSERVER
+  private:
+    void RemoveObservers();
+
+    nsInterfaceHashtable<nsCStringHashKey, nsISupports> mHash;
+    nsCString mCategory;
+    bool mObserversRemoved;
+};
+
+/**
+ * This is a helper class that caches services that are registered in a certain
+ * category. The intended usage is that a service stores a variable of type
+ * nsCategoryCache<nsIFoo> in a member variable, where nsIFoo is the interface
+ * that these services should implement. The constructor of this class should
+ * then get the name of the category.
+ */
+template<class T>
+class nsCategoryCache MOZ_FINAL
+{
+  public:
+    explicit nsCategoryCache(const char* aCategory)
+      : mCategoryName(aCategory)
+    {
+    }
+    ~nsCategoryCache() {
+      if (mObserver)
+	mObserver->ListenerDied();
+    }
+
+    void GetEntries(nsCOMArray<T>& result) {
+      // Lazy initialization, so that services in this category can't
+      // cause reentrant getService (bug 386376)
+      if (!mObserver)
+        mObserver = new nsCategoryObserver(mCategoryName.get());
+
+      mObserver->GetHash().EnumerateRead(EntriesToArray, &result);
+    }
+
+  private:
+    // Not to be implemented
+    nsCategoryCache(const nsCategoryCache<T>&);
+
+    static PLDHashOperator EntriesToArray(const nsACString& key,
+					  nsISupports* entry, void* arg)
+    {
+      nsCOMArray<T>& entries = *static_cast<nsCOMArray<T>*>(arg);
+
+      nsCOMPtr<T> service = do_QueryInterface(entry);
+      if (service) {
+	entries.AppendObject(service);
+      }
+      return PL_DHASH_NEXT;
+    }
+
+    nsCString mCategoryName;
+    nsRefPtr<nsCategoryObserver> mObserver;
+
+};
+
+#endif