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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/. */
+
+/*
+ * GC-internal definition of relocation overlay used while moving cells.
+ */
+
+#ifndef gc_RelocationOverlay_h
+#define gc_RelocationOverlay_h
+
+#include "mozilla/Assertions.h"
+
+#include <stdint.h>
+
+#include "gc/Cell.h"
+
+namespace js {
+namespace gc {
+
+/*
+ * This structure overlays a Cell that has been moved and provides a way to find
+ * its new location. It's used during generational and compacting GC.
+ */
+class RelocationOverlay : public Cell {
+ public:
+ /* The location the cell has been moved to, stored in the cell header. */
+ Cell* forwardingAddress() const {
+ MOZ_ASSERT(isForwarded());
+ return reinterpret_cast<Cell*>(header_.getForwardingAddress());
+ }
+
+ protected:
+ /* A list entry to track all relocated things. */
+ RelocationOverlay* next_;
+
+ explicit RelocationOverlay(Cell* dst);
+
+ public:
+ static const RelocationOverlay* fromCell(const Cell* cell) {
+ return static_cast<const RelocationOverlay*>(cell);
+ }
+
+ static RelocationOverlay* fromCell(Cell* cell) {
+ return static_cast<RelocationOverlay*>(cell);
+ }
+
+ static RelocationOverlay* forwardCell(Cell* src, Cell* dst);
+
+ void setNext(RelocationOverlay* next) {
+ MOZ_ASSERT(isForwarded());
+ next_ = next;
+ }
+
+ RelocationOverlay* next() const {
+ MOZ_ASSERT(isForwarded());
+ return next_;
+ }
+};
+
+} // namespace gc
+} // namespace js
+
+#endif /* gc_RelocationOverlay_h */