1 files changed, 84 insertions, 0 deletions
diff --git a/js/src/gc/HashUtil.h b/js/src/gc/HashUtil.h
new file mode 100644
index 0000000000..8202f994bd
--- /dev/null
+++ b/js/src/gc/HashUtil.h
@@ -0,0 +1,84 @@
+/* -*- 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 gc_HashUtil_h
+#define gc_HashUtil_h
+
+#include <type_traits>
+
+#include "vm/JSContext.h"
+
+namespace js {
+
+/*
+ * Used to add entries to a js::HashMap or HashSet where the key depends on a GC
+ * thing that may be moved by generational or compacting GC between the call to
+ * lookupForAdd() and relookupOrAdd().
+ */
+template <class T>
+struct DependentAddPtr {
+  using AddPtr = typename T::AddPtr;
+  using Entry = typename T::Entry;
+
+  template <class Lookup>
+  DependentAddPtr(const JSContext* cx, T& table, const Lookup& lookup)
+      : addPtr(table.lookupForAdd(lookup)),
+        originalGcNumber(cx->runtime()->gc.gcNumber()) {}
+
+  DependentAddPtr(DependentAddPtr&& other)
+      : addPtr(other.addPtr), originalGcNumber(other.originalGcNumber) {}
+
+  template <class KeyInput, class ValueInput>
+  bool add(JSContext* cx, T& table, const KeyInput& key,
+           const ValueInput& value) {
+    refreshAddPtr(cx, table, key);
+    if (!table.relookupOrAdd(addPtr, key, value)) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+    return true;
+  }
+
+  template <class KeyInput>
+  void remove(JSContext* cx, T& table, const KeyInput& key) {
+    refreshAddPtr(cx, table, key);
+    if (addPtr) {
+      table.remove(addPtr);
+    }
+  }
+
+  bool found() const { return addPtr.found(); }
+  explicit operator bool() const { return found(); }
+  const Entry& operator*() const { return *addPtr; }
+  const Entry* operator->() const { return &*addPtr; }
+
+ private:
+  AddPtr addPtr;
+  const uint64_t originalGcNumber;
+
+  template <class KeyInput>
+  void refreshAddPtr(JSContext* cx, T& table, const KeyInput& key) {
+    bool gcHappened = originalGcNumber != cx->runtime()->gc.gcNumber();
+    if (gcHappened) {
+      addPtr = table.lookupForAdd(key);
+    }
+  }
+
+  DependentAddPtr() = delete;
+  DependentAddPtr(const DependentAddPtr&) = delete;
+  DependentAddPtr& operator=(const DependentAddPtr&) = delete;
+};
+
+template <typename T, typename Lookup>
+inline auto MakeDependentAddPtr(const JSContext* cx, T& table,
+                                const Lookup& lookup) {
+  using Ptr = DependentAddPtr<std::remove_reference_t<decltype(table)>>;
+  return Ptr(cx, table, lookup);
+}
+
+}  // namespace js
+
+#endif