1 files changed, 67 insertions, 0 deletions
diff --git a/xpcom/ds/nsObserverList.h b/xpcom/ds/nsObserverList.h
new file mode 100644
index 0000000000..9f209e40d6
--- /dev/null
+++ b/xpcom/ds/nsObserverList.h
@@ -0,0 +1,67 @@
+/* -*- 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 nsObserverList_h___
+#define nsObserverList_h___
+
+#include "nsISupports.h"
+#include "nsCOMArray.h"
+#include "nsIObserver.h"
+#include "nsHashKeys.h"
+#include "nsMaybeWeakPtr.h"
+#include "nsSimpleEnumerator.h"
+#include "mozilla/Attributes.h"
+
+class nsObserverList : public nsCharPtrHashKey {
+  friend class nsObserverService;
+
+ public:
+  explicit nsObserverList(const char* aKey) : nsCharPtrHashKey(aKey) {
+    MOZ_COUNT_CTOR(nsObserverList);
+  }
+
+  nsObserverList(nsObserverList&& aOther)
+      : nsCharPtrHashKey(std::move(aOther)),
+        mObservers(std::move(aOther.mObservers)) {
+    MOZ_COUNT_CTOR(nsObserverList);
+  }
+
+  MOZ_COUNTED_DTOR(nsObserverList)
+
+  [[nodiscard]] nsresult AddObserver(nsIObserver* aObserver, bool aOwnsWeak);
+  [[nodiscard]] nsresult RemoveObserver(nsIObserver* aObserver);
+
+  void NotifyObservers(nsISupports* aSubject, const char* aTopic,
+                       const char16_t* aSomeData);
+  void GetObserverList(nsISimpleEnumerator** aEnumerator);
+
+  // Clone an array with the observers of this category.
+  // The array is filled in last-added-first order.
+  nsCOMArray<nsIObserver> ReverseCloneObserverArray();
+
+  // Like FillObserverArray(), but only for strongly held observers.
+  void AppendStrongObservers(nsCOMArray<nsIObserver>& aArray);
+
+ private:
+  nsMaybeWeakPtrArray<nsIObserver> mObservers;
+};
+
+class nsObserverEnumerator final : public nsSimpleEnumerator {
+ public:
+  NS_DECL_NSISIMPLEENUMERATOR
+
+  explicit nsObserverEnumerator(nsObserverList* aObserverList);
+
+  const nsID& DefaultInterface() override { return NS_GET_IID(nsIObserver); }
+
+ private:
+  ~nsObserverEnumerator() override = default;
+
+  int32_t mIndex;  // Counts up from 0
+  nsCOMArray<nsIObserver> mObservers;
+};
+
+#endif /* nsObserverList_h___ */