chromium/third_party/blink/renderer/platform/heap/thread_state_storage.h

// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_THREAD_STATE_STORAGE_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_THREAD_STATE_STORAGE_H_

#include <cstdint>

#include "base/compiler_specific.h"
#include "third_party/blink/renderer/platform/heap/thread_local.h"
#include "third_party/blink/renderer/platform/platform_export.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"

namespace cppgc {
class AllocationHandle;
class HeapHandle;
}  // namespace cppgc

namespace blink {

class ThreadState;
class ThreadStateStorage;

// ThreadAffinity indicates which threads objects can be used on. We
// distinguish between objects that can be used on the main thread
// only and objects that can be used on any thread.
//
// For objects that can only be used on the main thread, we avoid going
// through thread-local storage to get to the thread state. This is
// important for performance.
enum ThreadAffinity { … };

template <typename T, typename = void>
struct ThreadingTrait { … };

// Storage for all ThreadState objects. This includes the main-thread
// ThreadState as well. Keep it outside the class so that PLATFORM_EXPORT
// doesn't apply to it (otherwise, clang-cl complains).
extern constinit thread_local ThreadStateStorage* g_thread_specific_
    __attribute__((tls_model …));

// ThreadStateStorage is the explicitly managed TLS- and global-backed storage
// for ThreadState.
class PLATFORM_EXPORT ThreadStateStorage final { … };

template <ThreadAffinity>
class ThreadStateStorageFor;

template <>
class ThreadStateStorageFor<kMainThreadOnly> { … };

template <>
class ThreadStateStorageFor<kAnyThread> { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_THREAD_STATE_STORAGE_H_