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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_EMBEDDER_HEAP_H_
#define INCLUDE_V8_EMBEDDER_HEAP_H_
#include "v8-traced-handle.h" // NOLINT(build/include_directory)
#include "v8config.h" // NOLINT(build/include_directory)
namespace v8 {
namespace internal {
class TracedHandles;
} // namespace internal
class Isolate;
class Value;
/**
* Handler for embedder roots on non-unified heap garbage collections.
*/
class V8_EXPORT EmbedderRootsHandler {
public:
enum class RootHandling {
kQueryEmbedderForNonDroppableReferences,
kDontQueryEmbedderForAnyReference,
};
virtual ~EmbedderRootsHandler() = default;
EmbedderRootsHandler() = default;
explicit EmbedderRootsHandler(RootHandling default_traced_reference_handling)
: default_traced_reference_handling_(default_traced_reference_handling) {}
/**
* Returns true if the |TracedReference| handle should be considered as root
* for the currently running non-tracing garbage collection and false
* otherwise. The default implementation will keep all |TracedReference|
* references as roots.
*
* If this returns false, then V8 may decide that the object referred to by
* such a handle is reclaimed. In that case, V8 calls |ResetRoot()| for the
* |TracedReference|.
*
* Note that the `handle` is different from the handle that the embedder holds
* for retaining the object.
*
* The concrete implementations must be thread-safe.
*/
virtual bool IsRoot(const v8::TracedReference<v8::Value>& handle) = 0;
/**
* Used in combination with |IsRoot|. Called by V8 when an
* object that is backed by a handle is reclaimed by a non-tracing garbage
* collection. It is up to the embedder to reset the original handle.
*
* Note that the |handle| is different from the handle that the embedder holds
* for retaining the object. It is up to the embedder to find the original
* handle via the object or class id.
*/
virtual void ResetRoot(const v8::TracedReference<v8::Value>& handle) = 0;
/**
* Similar to |ResetRoot()|, but opportunistic. The function is called in
* parallel for different handles and as such must be thread-safe. In case,
* |false| is returned, |ResetRoot()| will be recalled for the same handle.
*/
virtual bool TryResetRoot(const v8::TracedReference<v8::Value>& handle) {
ResetRoot(handle);
return true;
}
private:
const RootHandling default_traced_reference_handling_ =
RootHandling::kQueryEmbedderForNonDroppableReferences;
friend class internal::TracedHandles;
};
} // namespace v8
#endif // INCLUDE_V8_EMBEDDER_HEAP_H_
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