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diff --git a/js/public/SweepingAPI.h b/js/public/SweepingAPI.h
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+/* -*- 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 js_SweepingAPI_h
+#define js_SweepingAPI_h
+
+#include "mozilla/LinkedList.h"
+#include "mozilla/Maybe.h"
+
+#include "jstypes.h"
+
+#include "js/GCAnnotations.h"
+#include "js/GCPolicyAPI.h"
+#include "js/RootingAPI.h"
+
+namespace js {
+namespace gc {
+
+class StoreBuffer;
+
+JS_PUBLIC_API void LockStoreBuffer(StoreBuffer* sb);
+JS_PUBLIC_API void UnlockStoreBuffer(StoreBuffer* sb);
+
+class AutoLockStoreBuffer {
+  StoreBuffer* sb;
+
+ public:
+  explicit AutoLockStoreBuffer(StoreBuffer* sb) : sb(sb) {
+    LockStoreBuffer(sb);
+  }
+  ~AutoLockStoreBuffer() { UnlockStoreBuffer(sb); }
+};
+
+}  // namespace gc
+}  // namespace js
+
+namespace JS {
+namespace detail {
+class WeakCacheBase;
+}  // namespace detail
+
+namespace shadow {
+JS_PUBLIC_API void RegisterWeakCache(JS::Zone* zone,
+                                     JS::detail::WeakCacheBase* cachep);
+JS_PUBLIC_API void RegisterWeakCache(JSRuntime* rt,
+                                     JS::detail::WeakCacheBase* cachep);
+}  // namespace shadow
+
+namespace detail {
+class WeakCacheBase : public mozilla::LinkedListElement<WeakCacheBase> {
+  WeakCacheBase() = delete;
+  explicit WeakCacheBase(const WeakCacheBase&) = delete;
+
+ public:
+  explicit WeakCacheBase(Zone* zone) { shadow::RegisterWeakCache(zone, this); }
+  explicit WeakCacheBase(JSRuntime* rt) { shadow::RegisterWeakCache(rt, this); }
+  WeakCacheBase(WeakCacheBase&& other) = default;
+  virtual ~WeakCacheBase() = default;
+
+  virtual size_t traceWeak(JSTracer* trc, js::gc::StoreBuffer* sbToLock) = 0;
+
+  // Sweeping will be skipped if the cache is empty already.
+  virtual bool empty() = 0;
+
+  // Enable/disable read barrier during incremental sweeping and set the tracer
+  // to use.
+  virtual bool setIncrementalBarrierTracer(JSTracer* trc) {
+    // Derived classes do not support incremental barriers by default.
+    return false;
+  }
+  virtual bool needsIncrementalBarrier() const {
+    // Derived classes do not support incremental barriers by default.
+    return false;
+  }
+};
+}  // namespace detail
+
+// A WeakCache stores the given Sweepable container and links itself into a
+// list of such caches that are swept during each GC. A WeakCache can be
+// specific to a zone, or across a whole runtime, depending on which
+// constructor is used.
+template <typename T>
+class WeakCache : protected detail::WeakCacheBase,
+                  public js::MutableWrappedPtrOperations<T, WeakCache<T>> {
+  T cache;
+
+ public:
+  using Type = T;
+
+  template <typename... Args>
+  explicit WeakCache(Zone* zone, Args&&... args)
+      : WeakCacheBase(zone), cache(std::forward<Args>(args)...) {}
+  template <typename... Args>
+  explicit WeakCache(JSRuntime* rt, Args&&... args)
+      : WeakCacheBase(rt), cache(std::forward<Args>(args)...) {}
+
+  const T& get() const { return cache; }
+  T& get() { return cache; }
+
+  size_t traceWeak(JSTracer* trc, js::gc::StoreBuffer* sbToLock) override {
+    // Take the store buffer lock in case sweeping triggers any generational
+    // post barriers. This is not always required and WeakCache specializations
+    // may delay or skip taking the lock as appropriate.
+    mozilla::Maybe<js::gc::AutoLockStoreBuffer> lock;
+    if (sbToLock) {
+      lock.emplace(sbToLock);
+    }
+
+    GCPolicy<T>::traceWeak(trc, &cache);
+    return 0;
+  }
+
+  bool empty() override { return cache.empty(); }
+} JS_HAZ_NON_GC_POINTER;
+
+}  // namespace JS
+
+#endif  // js_SweepingAPI_h