blob: fd845409077996fa90f6e6ab159e74302fd713b6 [file] [log] [blame]
/*
* Copyright (C) 2008, 2016 Apple Inc. All rights reserved.
* Copyright (C) 2009 Jian Li <jianli@chromium.org>
* Copyright (C) 2012 Patrick Gansterer <paroga@paroga.com>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of Apple Inc. ("Apple") nor the names of
* its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/* Thread local storage is implemented by using either pthread API or Windows
* native API. There is subtle semantic discrepancy for the cleanup function
* implementation as noted below:
* @ In pthread implementation, the destructor function will be called
* repeatedly if there is still non-NULL value associated with the function.
* @ In Windows native implementation, the destructor function will be called
* only once.
* This semantic discrepancy does not impose any problem because nowhere in
* WebKit the repeated call bahavior is utilized.
*/
#pragma once
#include <wtf/MainThread.h>
#include <wtf/Noncopyable.h>
#include <wtf/StdLibExtras.h>
#include <wtf/Threading.h>
namespace WTF {
enum class CanBeGCThread {
False,
True
};
template<typename T, CanBeGCThread canBeGCThread = CanBeGCThread::False> class ThreadSpecific {
WTF_MAKE_NONCOPYABLE(ThreadSpecific);
WTF_MAKE_FAST_ALLOCATED;
public:
ThreadSpecific();
bool isSet(); // Useful as a fast check to see if this thread has set this value.
T* operator->();
operator T*();
T& operator*();
private:
// Not implemented. It's technically possible to destroy a thread specific key, but one would need
// to make sure that all values have been destroyed already (usually, that all threads that used it
// have exited). It's unlikely that any user of this call will be in that situation - and having
// a destructor defined can be confusing, given that it has such strong pre-requisites to work correctly.
~ThreadSpecific();
struct Data {
WTF_MAKE_NONCOPYABLE(Data);
WTF_MAKE_FAST_ALLOCATED;
public:
using PointerType = typename std::remove_const<T>::type*;
Data(ThreadSpecific<T, canBeGCThread>* owner)
: owner(owner)
{
// Set up thread-specific value's memory pointer before invoking constructor, in case any function it calls
// needs to access the value, to avoid recursion.
owner->setInTLS(this);
new (NotNull, storagePointer()) T();
}
~Data()
{
storagePointer()->~T();
owner->setInTLS(nullptr);
}
PointerType storagePointer() const { return const_cast<PointerType>(reinterpret_cast<const T*>(&m_storage)); }
typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type m_storage;
ThreadSpecific<T, canBeGCThread>* owner;
};
T* get();
T* set();
void setInTLS(Data*);
void static THREAD_SPECIFIC_CALL destroy(void* ptr);
#if USE(PTHREADS)
pthread_key_t m_key { };
#elif OS(WINDOWS)
int m_index;
#endif
};
#if USE(PTHREADS)
template<typename T, CanBeGCThread canBeGCThread>
inline ThreadSpecific<T, canBeGCThread>::ThreadSpecific()
{
int error = pthread_key_create(&m_key, destroy);
if (error)
CRASH();
}
template<typename T, CanBeGCThread canBeGCThread>
inline T* ThreadSpecific<T, canBeGCThread>::get()
{
Data* data = static_cast<Data*>(pthread_getspecific(m_key));
if (data)
return data->storagePointer();
return nullptr;
}
template<typename T, CanBeGCThread canBeGCThread>
inline void ThreadSpecific<T, canBeGCThread>::setInTLS(Data* data)
{
pthread_setspecific(m_key, data);
}
#elif OS(WINDOWS)
// The maximum number of FLS keys that can be created. For simplification, we assume that:
// 1) Once the instance of ThreadSpecific<> is created, it will not be destructed until the program dies.
// 2) We do not need to hold many instances of ThreadSpecific<> data. This fixed number should be far enough.
static constexpr int maxFlsKeySize = 128;
WTF_EXPORT_PRIVATE long& flsKeyCount();
WTF_EXPORT_PRIVATE DWORD* flsKeys();
template<typename T, CanBeGCThread canBeGCThread>
inline ThreadSpecific<T, canBeGCThread>::ThreadSpecific()
: m_index(-1)
{
DWORD flsKey = FlsAlloc(destroy);
if (flsKey == FLS_OUT_OF_INDEXES)
CRASH();
m_index = InterlockedIncrement(&flsKeyCount()) - 1;
if (m_index >= maxFlsKeySize)
CRASH();
flsKeys()[m_index] = flsKey;
}
template<typename T, CanBeGCThread canBeGCThread>
inline ThreadSpecific<T, canBeGCThread>::~ThreadSpecific()
{
FlsFree(flsKeys()[m_index]);
}
template<typename T, CanBeGCThread canBeGCThread>
inline T* ThreadSpecific<T, canBeGCThread>::get()
{
Data* data = static_cast<Data*>(FlsGetValue(flsKeys()[m_index]));
if (data)
return data->storagePointer();
return nullptr;
}
template<typename T, CanBeGCThread canBeGCThread>
inline void ThreadSpecific<T, canBeGCThread>::setInTLS(Data* data)
{
FlsSetValue(flsKeys()[m_index], data);
}
#else
#error ThreadSpecific is not implemented for this platform.
#endif
template<typename T, CanBeGCThread canBeGCThread>
inline void THREAD_SPECIFIC_CALL ThreadSpecific<T, canBeGCThread>::destroy(void* ptr)
{
Data* data = static_cast<Data*>(ptr);
#if USE(PTHREADS)
// We want get() to keep working while data destructor works, because it can be called indirectly by the destructor.
// Some pthreads implementations zero out the pointer before calling destroy(), so we temporarily reset it.
pthread_setspecific(data->owner->m_key, ptr);
#endif
delete data;
}
template<typename T, CanBeGCThread canBeGCThread>
inline T* ThreadSpecific<T, canBeGCThread>::set()
{
RELEASE_ASSERT(canBeGCThread == CanBeGCThread::True || !Thread::mayBeGCThread());
ASSERT(!get());
Data* data = new Data(this); // Data will set itself into TLS.
ASSERT(get() == data->storagePointer());
return data->storagePointer();
}
template<typename T, CanBeGCThread canBeGCThread>
inline bool ThreadSpecific<T, canBeGCThread>::isSet()
{
return !!get();
}
template<typename T, CanBeGCThread canBeGCThread>
inline ThreadSpecific<T, canBeGCThread>::operator T*()
{
if (T* ptr = get())
return ptr;
return set();
}
template<typename T, CanBeGCThread canBeGCThread>
inline T* ThreadSpecific<T, canBeGCThread>::operator->()
{
return operator T*();
}
template<typename T, CanBeGCThread canBeGCThread>
inline T& ThreadSpecific<T, canBeGCThread>::operator*()
{
return *operator T*();
}
} // namespace WTF
using WTF::ThreadSpecific;