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v8/include/v8-weak-callback-info.h

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+// Copyright 2021 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_V8_WEAK_CALLBACK_INFO_H_
+#define INCLUDE_V8_WEAK_CALLBACK_INFO_H_
+
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace v8 {
+
+class Isolate;
+
+namespace api_internal {
+V8_EXPORT void InternalFieldOutOfBounds(int index);
+}  // namespace api_internal
+
+static const int kInternalFieldsInWeakCallback = 2;
+static const int kEmbedderFieldsInWeakCallback = 2;
+
+template <typename T>
+class WeakCallbackInfo {
+ public:
+  using Callback = void (*)(const WeakCallbackInfo<T>& data);
+
+  WeakCallbackInfo(Isolate* isolate, T* parameter,
+                   void* embedder_fields[kEmbedderFieldsInWeakCallback],
+                   Callback* callback)
+      : isolate_(isolate), parameter_(parameter), callback_(callback) {
+    for (int i = 0; i < kEmbedderFieldsInWeakCallback; ++i) {
+      embedder_fields_[i] = embedder_fields[i];
+    }
+  }
+
+  V8_INLINE Isolate* GetIsolate() const { return isolate_; }
+  V8_INLINE T* GetParameter() const { return parameter_; }
+  V8_INLINE void* GetInternalField(int index) const;
+
+  // When first called, the embedder MUST Reset() the Global which triggered the
+  // callback. The Global itself is unusable for anything else. No v8 other api
+  // calls may be called in the first callback. Should additional work be
+  // required, the embedder must set a second pass callback, which will be
+  // called after all the initial callbacks are processed.
+  // Calling SetSecondPassCallback on the second pass will immediately crash.
+  void SetSecondPassCallback(Callback callback) const { *callback_ = callback; }
+
+ private:
+  Isolate* isolate_;
+  T* parameter_;
+  Callback* callback_;
+  void* embedder_fields_[kEmbedderFieldsInWeakCallback];
+};
+
+/**
+ * Weakness type for weak handles.
+ */
+enum class WeakCallbackType {
+  /**
+   * Passes a user-defined void* parameter back to the callback.
+   */
+  kParameter,
+  /**
+   * Passes the first two internal fields of the object back to the callback.
+   */
+  kInternalFields,
+};
+
+template <class T>
+void* WeakCallbackInfo<T>::GetInternalField(int index) const {
+#ifdef V8_ENABLE_CHECKS
+  if (index < 0 || index >= kEmbedderFieldsInWeakCallback) {
+    api_internal::InternalFieldOutOfBounds(index);
+  }
+#endif
+  return embedder_fields_[index];
+}
+
+}  // namespace v8
+
+#endif  // INCLUDE_V8_WEAK_CALLBACK_INFO_H_