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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Cross-platform lightweight thread local data wrappers. */
#ifndef mozilla_ThreadLocal_h
#define mozilla_ThreadLocal_h
#if !defined(XP_WIN)
# include <pthread.h>
# include <signal.h>
#endif
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/TypeTraits.h"
namespace mozilla {
// sig_safe_t denotes an atomic type which can be read or stored in a single
// instruction. This means that data of this type is safe to be manipulated
// from a signal handler, or other similar asynchronous execution contexts.
#if defined(XP_WIN)
typedef unsigned long sig_safe_t;
#else
typedef sig_atomic_t sig_safe_t;
#endif
namespace detail {
#if defined(HAVE_THREAD_TLS_KEYWORD) || defined(XP_WIN) || defined(XP_MACOSX)
#define MOZ_HAS_THREAD_LOCAL
#endif
/*
* Thread Local Storage helpers.
*
* Usage:
*
* Do not directly instantiate this class. Instead, use the
* MOZ_THREAD_LOCAL macro to declare or define instances. The macro
* takes a type name as its argument.
*
* Declare like this:
* extern MOZ_THREAD_LOCAL(int) tlsInt;
* Define like this:
* MOZ_THREAD_LOCAL(int) tlsInt;
* or:
* static MOZ_THREAD_LOCAL(int) tlsInt;
*
* Only static-storage-duration (e.g. global variables, or static class members)
* objects of this class should be instantiated. This class relies on
* zero-initialization, which is implicit for static-storage-duration objects.
* It doesn't have a custom default constructor, to avoid static initializers.
*
* API usage:
*
* // Create a TLS item.
* //
* // Note that init() should be invoked before the first use of set()
* // or get(). It is ok to call it multiple times. This must be
* // called in a way that avoids possible races with other threads.
* MOZ_THREAD_LOCAL(int) tlsKey;
* if (!tlsKey.init()) {
* // deal with the error
* }
*
* // Set the TLS value
* tlsKey.set(123);
*
* // Get the TLS value
* int value = tlsKey.get();
*/
template<typename T>
class ThreadLocal
{
#ifndef MOZ_HAS_THREAD_LOCAL
typedef pthread_key_t key_t;
// Integral types narrower than void* must be extended to avoid
// warnings from valgrind on some platforms. This helper type
// achieves that without penalizing the common case of ThreadLocals
// instantiated using a pointer type.
template<typename S>
struct Helper
{
typedef uintptr_t Type;
};
template<typename S>
struct Helper<S *>
{
typedef S *Type;
};
#endif
bool initialized() const {
#ifdef MOZ_HAS_THREAD_LOCAL
return true;
#else
return mInited;
#endif
}
public:
// __thread does not allow non-trivial constructors, but we can
// instead rely on zero-initialization.
#ifndef MOZ_HAS_THREAD_LOCAL
ThreadLocal()
: mKey(0), mInited(false)
{}
#endif
MOZ_MUST_USE inline bool init();
inline T get() const;
inline void set(const T aValue);
private:
#ifdef MOZ_HAS_THREAD_LOCAL
T mValue;
#else
key_t mKey;
bool mInited;
#endif
};
template<typename T>
inline bool
ThreadLocal<T>::init()
{
static_assert(mozilla::IsPointer<T>::value || mozilla::IsIntegral<T>::value,
"mozilla::ThreadLocal must be used with a pointer or "
"integral type");
static_assert(sizeof(T) <= sizeof(void*),
"mozilla::ThreadLocal can't be used for types larger than "
"a pointer");
#ifdef MOZ_HAS_THREAD_LOCAL
return true;
#else
if (!initialized()) {
mInited = !pthread_key_create(&mKey, nullptr);
}
return mInited;
#endif
}
template<typename T>
inline T
ThreadLocal<T>::get() const
{
#ifdef MOZ_HAS_THREAD_LOCAL
return mValue;
#else
MOZ_ASSERT(initialized());
void* h;
h = pthread_getspecific(mKey);
return static_cast<T>(reinterpret_cast<typename Helper<T>::Type>(h));
#endif
}
template<typename T>
inline void
ThreadLocal<T>::set(const T aValue)
{
#ifdef MOZ_HAS_THREAD_LOCAL
mValue = aValue;
#else
MOZ_ASSERT(initialized());
void* h = reinterpret_cast<void*>(static_cast<typename Helper<T>::Type>(aValue));
bool succeeded = !pthread_setspecific(mKey, h);
if (!succeeded) {
MOZ_CRASH();
}
#endif
}
#ifdef MOZ_HAS_THREAD_LOCAL
#if defined(XP_WIN) || defined(XP_MACOSX)
#define MOZ_THREAD_LOCAL(TYPE) thread_local mozilla::detail::ThreadLocal<TYPE>
#else
#define MOZ_THREAD_LOCAL(TYPE) __thread mozilla::detail::ThreadLocal<TYPE>
#endif
#else
#define MOZ_THREAD_LOCAL(TYPE) mozilla::detail::ThreadLocal<TYPE>
#endif
} // namespace detail
} // namespace mozilla
#endif /* mozilla_ThreadLocal_h */
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