1 files changed, 123 insertions, 0 deletions
diff --git a/xpcom/components/nsCategoryCache.h b/xpcom/components/nsCategoryCache.h
new file mode 100644
index 0000000000..f2d7ba32a3
--- /dev/null
+++ b/xpcom/components/nsCategoryCache.h
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "nsIObserver.h"
+
+#include "nsServiceManagerUtils.h"
+
+#include "nsCOMArray.h"
+#include "nsInterfaceHashtable.h"
+
+#include "nsXPCOM.h"
+#include "MainThreadUtils.h"
+
+class nsCategoryObserver final : public nsIObserver {
+  ~nsCategoryObserver();
+
+ public:
+  explicit nsCategoryObserver(const nsACString& aCategory);
+
+  void ListenerDied();
+  void SetListener(void(aCallback)(void*), void* aClosure);
+  nsInterfaceHashtable<nsCStringHashKey, nsISupports>& GetHash() {
+    return mHash;
+  }
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+ private:
+  void RemoveObservers();
+
+  nsInterfaceHashtable<nsCStringHashKey, nsISupports> mHash;
+  nsCString mCategory;
+  void (*mCallback)(void*);
+  void* mClosure;
+  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 final {
+ public:
+  explicit nsCategoryCache(const char* aCategory) : mCategoryName(aCategory) {
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+  ~nsCategoryCache() {
+    MOZ_ASSERT(NS_IsMainThread());
+    if (mObserver) {
+      mObserver->ListenerDied();
+    }
+  }
+
+  void GetEntries(nsCOMArray<T>& aResult) {
+    MOZ_ASSERT(NS_IsMainThread());
+    LazyInit();
+
+    AddEntries(aResult);
+  }
+
+  /**
+   * This function returns an nsCOMArray of interface pointers to the cached
+   * category enries for the requested category.  This was added in order to be
+   * used in call sites where the overhead of excessive allocations can be
+   * unacceptable.  See bug 1360971 for an example.
+   */
+  const nsCOMArray<T>& GetCachedEntries() {
+    MOZ_ASSERT(NS_IsMainThread());
+    LazyInit();
+
+    if (mCachedEntries.IsEmpty()) {
+      AddEntries(mCachedEntries);
+    }
+    return mCachedEntries;
+  }
+
+ private:
+  void LazyInit() {
+    // Lazy initialization, so that services in this category can't
+    // cause reentrant getService (bug 386376)
+    if (!mObserver) {
+      mObserver = new nsCategoryObserver(mCategoryName);
+      mObserver->SetListener(nsCategoryCache<T>::OnCategoryChanged, this);
+    }
+  }
+
+  void AddEntries(nsCOMArray<T>& aResult) {
+    for (nsISupports* entry : mObserver->GetHash().Values()) {
+      nsCOMPtr<T> service = do_QueryInterface(entry);
+      if (service) {
+        aResult.AppendElement(service.forget());
+      }
+    }
+  }
+
+  static void OnCategoryChanged(void* aClosure) {
+    MOZ_ASSERT(NS_IsMainThread());
+    auto self = static_cast<nsCategoryCache<T>*>(aClosure);
+    self->mCachedEntries.Clear();
+  }
+
+ private:
+  // Not to be implemented
+  nsCategoryCache(const nsCategoryCache<T>&);
+
+  nsCString mCategoryName;
+  RefPtr<nsCategoryObserver> mObserver;
+  nsCOMArray<T> mCachedEntries;
+};
+
+#endif