chromium/v8/include/cppgc/cross-thread-persistent.h

// 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_CROSS_THREAD_PERSISTENT_H_
#define INCLUDE_CPPGC_CROSS_THREAD_PERSISTENT_H_

#include <atomic>

#include "cppgc/internal/persistent-node.h"
#include "cppgc/internal/pointer-policies.h"
#include "cppgc/persistent.h"
#include "cppgc/visitor.h"

namespace cppgc {
namespace internal {

// Wrapper around PersistentBase that allows accessing poisoned memory when
// using ASAN. This is needed as the GC of the heap that owns the value
// of a CTP, may clear it (heap termination, weakness) while the object
// holding the CTP may be poisoned as itself may be deemed dead.
class CrossThreadPersistentBase : public PersistentBase { … };

template <typename T, typename WeaknessPolicy, typename LocationPolicy,
          typename CheckingPolicy>
class BasicCrossThreadPersistent final : public CrossThreadPersistentBase,
                                         public LocationPolicy,
                                         private WeaknessPolicy,
                                         private CheckingPolicy { … };

IsWeak<BasicCrossThreadPersistent<T, internal::WeakCrossThreadPersistentPolicy, LocationPolicy, CheckingPolicy>>;

}  // namespace internal

namespace subtle {

/**
 * **DO NOT USE: Has known caveats, see below.**
 *
 * CrossThreadPersistent allows retaining objects from threads other than the
 * thread the owning heap is operating on.
 *
 * Known caveats:
 * - Does not protect the heap owning an object from terminating.
 * - Reaching transitively through the graph is unsupported as objects may be
 *   moved concurrently on the thread owning the object.
 */
CrossThreadPersistent;

/**
 * **DO NOT USE: Has known caveats, see below.**
 *
 * CrossThreadPersistent allows weakly retaining objects from threads other than
 * the thread the owning heap is operating on.
 *
 * Known caveats:
 * - Does not protect the heap owning an object from terminating.
 * - Reaching transitively through the graph is unsupported as objects may be
 *   moved concurrently on the thread owning the object.
 */
WeakCrossThreadPersistent;

}  // namespace subtle
}  // namespace cppgc

#endif  // INCLUDE_CPPGC_CROSS_THREAD_PERSISTENT_H_