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persistent-node.h
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109 lines (82 loc) · 2.59 KB
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// 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_