1 files changed, 109 insertions, 0 deletions
diff --git a/deps/v8/include/cppgc/internal/persistent-node.h b/deps/v8/include/cppgc/internal/persistent-node.h
new file mode 100644
index 00000000000..11cf69623e8
--- /dev/null
+++ b/deps/v8/include/cppgc/internal/persistent-node.h
@@ -0,0 +1,109 @@
+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef INCLUDE_CPPGC_INTERNAL_PERSISTENT_NODE_H_
+#define INCLUDE_CPPGC_INTERNAL_PERSISTENT_NODE_H_
+
+#include <array>
+#include <memory>
+#include <vector>
+
+#include "cppgc/internal/logging.h"
+#include "cppgc/trace-trait.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+
+class Visitor;
+
+namespace internal {
+
+// PersistentNode represesents a variant of two states:
+// 1) traceable node with a back pointer to the Persistent object;
+// 2) freelist entry.
+class PersistentNode final {
+ public:
+  PersistentNode() = default;
+
+  PersistentNode(const PersistentNode&) = delete;
+  PersistentNode& operator=(const PersistentNode&) = delete;
+
+  void InitializeAsUsedNode(void* owner, TraceCallback trace) {
+    owner_ = owner;
+    trace_ = trace;
+  }
+
+  void InitializeAsFreeNode(PersistentNode* next) {
+    next_ = next;
+    trace_ = nullptr;
+  }
+
+  void UpdateOwner(void* owner) {
+    CPPGC_DCHECK(IsUsed());
+    owner_ = owner;
+  }
+
+  PersistentNode* FreeListNext() const {
+    CPPGC_DCHECK(!IsUsed());
+    return next_;
+  }
+
+  void Trace(Visitor* visitor) const {
+    CPPGC_DCHECK(IsUsed());
+    trace_(visitor, owner_);
+  }
+
+  bool IsUsed() const { return trace_; }
+
+ private:
+  // PersistentNode acts as a designated union:
+  // If trace_ != nullptr, owner_ points to the corresponding Persistent handle.
+  // Otherwise, next_ points to the next freed PersistentNode.
+  union {
+    void* owner_ = nullptr;
+    PersistentNode* next_;
+  };
+  TraceCallback trace_ = nullptr;
+};
+
+class V8_EXPORT PersistentRegion {
+  using PersistentNodeSlots = std::array<PersistentNode, 256u>;
+
+ public:
+  PersistentRegion() = default;
+
+  PersistentRegion(const PersistentRegion&) = delete;
+  PersistentRegion& operator=(const PersistentRegion&) = delete;
+
+  PersistentNode* AllocateNode(void* owner, TraceCallback trace) {
+    if (!free_list_head_) {
+      EnsureNodeSlots();
+    }
+    PersistentNode* node = free_list_head_;
+    free_list_head_ = free_list_head_->FreeListNext();
+    node->InitializeAsUsedNode(owner, trace);
+    return node;
+  }
+
+  void FreeNode(PersistentNode* node) {
+    node->InitializeAsFreeNode(free_list_head_);
+    free_list_head_ = node;
+  }
+
+  void Trace(Visitor*);
+
+  size_t NodesInUse() const;
+
+ private:
+  void EnsureNodeSlots();
+
+  std::vector<std::unique_ptr<PersistentNodeSlots>> nodes_;
+  PersistentNode* free_list_head_ = nullptr;
+};
+
+}  // namespace internal
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_PERSISTENT_NODE_H_