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-rw-r--r--xpcom/base/nsMaybeWeakPtr.h169
1 files changed, 169 insertions, 0 deletions
diff --git a/xpcom/base/nsMaybeWeakPtr.h b/xpcom/base/nsMaybeWeakPtr.h
new file mode 100644
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+++ b/xpcom/base/nsMaybeWeakPtr.h
@@ -0,0 +1,169 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 nsMaybeWeakPtr_h_
+#define nsMaybeWeakPtr_h_
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Try.h"
+#include "nsCOMPtr.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsTArray.h"
+#include "nsCycleCollectionNoteChild.h"
+
+// nsMaybeWeakPtr is a helper object to hold a strong-or-weak reference
+// to the template class. It's pretty minimal, but sufficient.
+
+template <class T>
+class nsMaybeWeakPtr {
+ public:
+ nsMaybeWeakPtr() = default;
+ MOZ_IMPLICIT nsMaybeWeakPtr(T* aRef) : mPtr(aRef), mWeak(false) {}
+ MOZ_IMPLICIT nsMaybeWeakPtr(const nsCOMPtr<nsIWeakReference>& aRef)
+ : mPtr(aRef), mWeak(true) {}
+
+ nsMaybeWeakPtr<T>& operator=(T* aRef) {
+ mPtr = aRef;
+ mWeak = false;
+ return *this;
+ }
+
+ nsMaybeWeakPtr<T>& operator=(const nsCOMPtr<nsIWeakReference>& aRef) {
+ mPtr = aRef;
+ mWeak = true;
+ return *this;
+ }
+
+ bool operator==(const nsMaybeWeakPtr<T>& other) const {
+ return mPtr == other.mPtr;
+ }
+
+ nsISupports* GetRawValue() const { return mPtr.get(); }
+ bool IsWeak() const { return mWeak; }
+
+ const nsCOMPtr<T> GetValue() const;
+
+ private:
+ nsCOMPtr<nsISupports> mPtr;
+ bool mWeak;
+};
+
+// nsMaybeWeakPtrArray is an array of MaybeWeakPtr objects, that knows how to
+// grab a weak reference to a given object if requested. It only allows a
+// given object to appear in the array once.
+
+template <class T>
+class nsMaybeWeakPtrArray : public CopyableTArray<nsMaybeWeakPtr<T>> {
+ typedef nsTArray<nsMaybeWeakPtr<T>> MaybeWeakArray;
+
+ nsresult SetMaybeWeakPtr(nsMaybeWeakPtr<T>& aRef, T* aElement,
+ bool aOwnsWeak) {
+ nsresult rv = NS_OK;
+
+ if (aOwnsWeak) {
+ aRef = do_GetWeakReference(aElement, &rv);
+ } else {
+ aRef = aElement;
+ }
+
+ return rv;
+ }
+
+ public:
+ nsresult AppendWeakElement(T* aElement, bool aOwnsWeak) {
+ nsMaybeWeakPtr<T> ref;
+ MOZ_TRY(SetMaybeWeakPtr(ref, aElement, aOwnsWeak));
+
+ MaybeWeakArray::AppendElement(ref);
+ return NS_OK;
+ }
+
+ nsresult AppendWeakElementUnlessExists(T* aElement, bool aOwnsWeak) {
+ nsMaybeWeakPtr<T> ref;
+ MOZ_TRY(SetMaybeWeakPtr(ref, aElement, aOwnsWeak));
+
+ if (MaybeWeakArray::Contains(ref)) {
+ return NS_ERROR_INVALID_ARG;
+ }
+
+ MaybeWeakArray::AppendElement(ref);
+ return NS_OK;
+ }
+
+ nsresult RemoveWeakElement(T* aElement) {
+ if (MaybeWeakArray::RemoveElement(aElement)) {
+ return NS_OK;
+ }
+
+ // Don't use do_GetWeakReference; it should only be called if we know
+ // the object supports weak references.
+ nsCOMPtr<nsISupportsWeakReference> supWeakRef = do_QueryInterface(aElement);
+ if (!supWeakRef) {
+ return NS_ERROR_INVALID_ARG;
+ }
+
+ nsCOMPtr<nsIWeakReference> weakRef;
+ nsresult rv = supWeakRef->GetWeakReference(getter_AddRefs(weakRef));
+ NS_ENSURE_SUCCESS(rv, rv);
+
+ if (MaybeWeakArray::RemoveElement(weakRef)) {
+ return NS_OK;
+ }
+
+ return NS_ERROR_INVALID_ARG;
+ }
+};
+
+template <class T>
+const nsCOMPtr<T> nsMaybeWeakPtr<T>::GetValue() const {
+ if (!mPtr) {
+ return nullptr;
+ }
+
+ nsCOMPtr<T> ref;
+ nsresult rv;
+
+ if (mWeak) {
+ nsCOMPtr<nsIWeakReference> weakRef = do_QueryInterface(mPtr);
+ if (NS_WARN_IF(!weakRef)) {
+ return nullptr;
+ }
+ ref = do_QueryReferent(weakRef, &rv);
+ NS_WARNING_ASSERTION(NS_SUCCEEDED(rv) || rv == NS_ERROR_NULL_POINTER,
+ "QueryReferent failed with non-null pointer");
+ } else {
+ ref = do_QueryInterface(mPtr, &rv);
+ NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+ "QueryInterface failed with non-null pointer");
+ }
+ return ref;
+}
+
+template <typename T>
+inline void ImplCycleCollectionUnlink(nsMaybeWeakPtrArray<T>& aField) {
+ aField.Clear();
+}
+
+template <typename E>
+inline void ImplCycleCollectionTraverse(
+ nsCycleCollectionTraversalCallback& aCallback,
+ nsMaybeWeakPtrArray<E>& aField, const char* aName, uint32_t aFlags = 0) {
+ aFlags |= CycleCollectionEdgeNameArrayFlag;
+ size_t length = aField.Length();
+ for (size_t i = 0; i < length; ++i) {
+ CycleCollectionNoteChild(aCallback, aField[i].GetRawValue(), aName, aFlags);
+ }
+}
+
+// Call a method on each element in the array, but only if the element is
+// non-null.
+
+#define ENUMERATE_WEAKARRAY(array, type, method) \
+ for (uint32_t array_idx = 0; array_idx < array.Length(); ++array_idx) { \
+ const nsCOMPtr<type>& e = array.ElementAt(array_idx).GetValue(); \
+ if (e) e->method; \
+ }
+
+#endif