зеркало из https://github.com/mozilla/gecko-dev.git
97 строки
3.2 KiB
C++
97 строки
3.2 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_freestanding_SafeThreadLocal_h
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#define mozilla_freestanding_SafeThreadLocal_h
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#include <type_traits>
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#include "mozilla/NativeNt.h"
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#include "mozilla/ThreadLocal.h"
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namespace mozilla {
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namespace freestanding {
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// We cannot fall back to the Tls* APIs because kernel32 might not have been
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// loaded yet.
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#if defined(__MINGW32__) && !defined(HAVE_THREAD_TLS_KEYWORD)
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# error "This code requires the compiler to have native TLS support"
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#endif // defined(__MINGW32__) && !defined(HAVE_THREAD_TLS_KEYWORD)
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/**
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* This class holds data as a thread-local variable, or as a global variable
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* if the thread local storage is not initialized yet. It should be safe
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* because in that early stage we assume there is no more than a single thread.
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*/
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template <typename T>
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class SafeThreadLocal final {
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static MOZ_THREAD_LOCAL(T) sThreadLocal;
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static T sGlobal;
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static bool sIsTlsUsed;
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// In normal cases, TLS is always available and the class uses sThreadLocal
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// without changing sMainThreadId. So sMainThreadId is likely to be 0.
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//
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// If TLS is not available, we use sGlobal instead and update sMainThreadId
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// so that that thread keeps using sGlobal even after TLS is initialized
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// later.
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static DWORD sMainThreadId;
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// Need non-inline accessors to prevent the compiler from generating code
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// accessing sThreadLocal before checking a condition.
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MOZ_NEVER_INLINE static void SetGlobalValue(T aValue) { sGlobal = aValue; }
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MOZ_NEVER_INLINE static T GetGlobalValue() { return sGlobal; }
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public:
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static void set(T aValue) {
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static_assert(std::is_pointer_v<T>,
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"SafeThreadLocal must be used with a pointer");
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if (sMainThreadId == mozilla::nt::RtlGetCurrentThreadId()) {
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SetGlobalValue(aValue);
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} else if (sIsTlsUsed) {
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MOZ_ASSERT(mozilla::nt::RtlGetThreadLocalStoragePointer(),
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"Once TLS is used, TLS should be available till the end.");
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sThreadLocal.set(aValue);
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} else if (mozilla::nt::RtlGetThreadLocalStoragePointer()) {
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sIsTlsUsed = true;
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sThreadLocal.set(aValue);
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} else {
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MOZ_ASSERT(sMainThreadId == 0,
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"A second thread cannot be created before TLS is available.");
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sMainThreadId = mozilla::nt::RtlGetCurrentThreadId();
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SetGlobalValue(aValue);
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}
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}
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static T get() {
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if (sMainThreadId == mozilla::nt::RtlGetCurrentThreadId()) {
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return GetGlobalValue();
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} else if (sIsTlsUsed) {
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return sThreadLocal.get();
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}
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return GetGlobalValue();
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}
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};
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template <typename T>
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MOZ_THREAD_LOCAL(T)
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SafeThreadLocal<T>::sThreadLocal;
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template <typename T>
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T SafeThreadLocal<T>::sGlobal = nullptr;
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template <typename T>
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bool SafeThreadLocal<T>::sIsTlsUsed = false;
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template <typename T>
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DWORD SafeThreadLocal<T>::sMainThreadId = 0;
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} // namespace freestanding
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} // namespace mozilla
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#endif // mozilla_freestanding_SafeThreadLocal_h
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