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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
#include "qthreadstorage.h"
#include "qthreadstorage_p.h"
#include "private/qcoreapplication_p.h"
#include "qthread.h"
#include "qthread_p.h"
#include "qmutex.h"
#include <string.h>
QT_BEGIN_NAMESPACE
// #define THREADSTORAGE_DEBUG
#ifdef THREADSTORAGE_DEBUG
# define DEBUG_MSG qtsDebug
# include <stdio.h>
# include <stdarg.h>
void qtsDebug(const char *fmt, ...)
{
va_list va;
va_start(va, fmt);
fprintf(stderr, "QThreadStorage: ");
vfprintf(stderr, fmt, va);
fprintf(stderr, "\n");
va_end(va);
}
#else
# define DEBUG_MSG if (false)qDebug
#endif
Q_CONSTINIT static QBasicMutex destructorsMutex;
typedef QList<void (*)(void *)> DestructorMap;
Q_GLOBAL_STATIC(DestructorMap, destructors)
QThreadStorageData::QThreadStorageData(void (*func)(void *))
{
QMutexLocker locker(&destructorsMutex);
DestructorMap *destr = destructors();
if (!destr) {
/*
the destructors vector has already been destroyed, yet a new
QThreadStorage is being allocated. this can only happen during global
destruction, at which point we assume that there is only one thread.
in order to keep QThreadStorage working, we need somewhere to store
the data, best place we have in this situation is at the tail of the
current thread's tls vector. the destructor is ignored, since we have
no where to store it, and no way to actually call it.
*/
QThreadData *data = QThreadData::current();
id = data->tls.size();
DEBUG_MSG("QThreadStorageData: Allocated id %d, destructor %p cannot be stored", id, func);
return;
}
for (id = 0; id < destr->size(); id++) {
if (destr->at(id) == nullptr)
break;
}
if (id == destr->size()) {
destr->append(func);
} else {
(*destr)[id] = func;
}
DEBUG_MSG("QThreadStorageData: Allocated id %d, destructor %p", id, func);
}
QThreadStorageData::~QThreadStorageData()
{
DEBUG_MSG("QThreadStorageData: Released id %d", id);
QMutexLocker locker(&destructorsMutex);
if (destructors())
(*destructors())[id] = nullptr;
}
void **QThreadStorageData::get() const
{
QThreadData *data = QThreadData::current();
QList<void *> &tls = data->tls;
if (tls.size() <= id)
tls.resize(id + 1);
void **v = &tls[id];
DEBUG_MSG("QThreadStorageData: Returning storage %d, data %p, for thread %p",
id,
*v,
data->thread.loadRelaxed());
return *v ? v : nullptr;
}
void **QThreadStorageData::set(void *p)
{
QThreadData *data = QThreadData::current();
QList<void *> &tls = data->tls;
if (tls.size() <= id)
tls.resize(id + 1);
void* *ptr = &tls[id];
if (*ptr == p) // pointer-based setLocalData(localData()) → must be no-op
return ptr;
// delete any previous data
if (*ptr != nullptr) {
DEBUG_MSG("QThreadStorageData: Deleting previous storage %d, data %p, for thread %p",
id,
*ptr,
data->thread.loadRelaxed());
QMutexLocker locker(&destructorsMutex);
DestructorMap *destr = destructors();
void (*destructor)(void *) = destr ? destr->value(id) : nullptr;
locker.unlock();
if (destructor) {
void *q = std::exchange(*ptr, nullptr);
destructor(q);
// `destructor` may have re-entered and grown `tls`; re-seat `ptr`:
ptr = &tls[id];
}
}
// store new data
*ptr = p;
DEBUG_MSG("QThreadStorageData: Set storage %d for thread %p to %p", id, data->thread.loadRelaxed(), p);
return ptr;
}
void QThreadStorageData::clear()
{
// Skip if this thread doesn't have a QThreadData (anymore): there's
// nothing to clear, then, and set() would otherwise re-create it, here,
// during shutdown, with nothing left to destroy it again.
if (QThreadData::currentThreadData())
set(nullptr);
}
void QThreadStoragePrivate::init()
{
// Make sure the Q_GLOBAL_STATIC is initialized, ensuring consistent
// destruction order.
destructors();
}
void QThreadStoragePrivate::finish(QList<void *> *tls, bool suppressWarnings)
{
if (tls->isEmpty() || !destructors())
return; // nothing to do
if (!QCoreApplication::instanceExists())
suppressWarnings = true;
DEBUG_MSG("QThreadStorageData: Destroying storage for thread %p", QThread::currentThread());
while (!tls->isEmpty()) {
void *&value = tls->last();
void *q = value;
value = nullptr;
int i = tls->size() - 1;
tls->resize(i);
if (!q) {
// data already deleted
continue;
}
QMutexLocker locker(&destructorsMutex);
void (*destructor)(void *) = destructors()->value(i);
locker.unlock();
if (!destructor) {
if (!suppressWarnings)
qWarning("QThreadStorage: entry %d destroyed before end of thread %p",
i, QThread::currentThread());
continue;
}
destructor(q); //crash here might mean the thread exited after qthreadstorage was destroyed
if (tls->size() > i) {
//re reset the tls in case it has been recreated by its own destructor.
(*tls)[i] = nullptr;
}
}
tls->clear();
}
/*!
\class QThreadStorage
\inmodule QtCore
\brief The QThreadStorage class provides per-thread data storage.
\threadsafe
\ingroup thread
QThreadStorage is a template class where the template parameter \a T
specifies the type of data stored per-thread.
The setLocalData() function stores a single thread-specific value
for the calling thread. The data can be accessed later using
localData().
The hasLocalData() function allows the programmer to determine if
data has previously been set using the setLocalData() function.
This is also useful for lazy initialization.
If T is a pointer type, QThreadStorage takes ownership of the data
(which must be created on the heap with \c new) and deletes it when
the thread exits, either normally or via termination.
For example, the following code uses QThreadStorage to store a
single cache for each thread that calls the cacheObject() and
removeFromCache() functions. The cache is automatically
deleted when the calling thread exits.
\snippet threads/threads.cpp 7
\snippet threads/threads.cpp 8
\snippet threads/threads.cpp 9
\section1 Caveats
\list
\target qthreadstorage-shutdown-caveat
\li Calling hasLocalData(), localData() or setLocalData() during thread or
program shutdown may re-create the thread-local storage for the current
thread with nothing left to destroy it afterwards. The clearLocalData()
function is the only one that is unconditionally safe to call during
shutdown.
\li The QThreadStorage destructor does not delete per-thread data.
QThreadStorage only deletes per-thread data when the thread exits
or when setLocalData() is called multiple times.
\li QThreadStorage can be used to store data for the \c main()
thread. QThreadStorage deletes all data set for the \c main()
thread when QApplication is destroyed, regardless of whether or
not the \c main() thread has actually finished.
\endlist
\sa QThread
*/
/*!
\fn template <class T> QThreadStorage<T>::QThreadStorage()
Constructs a new per-thread data storage object.
*/
/*!
\fn template <class T> QThreadStorage<T>::~QThreadStorage()
Destroys the per-thread data storage object.
Note: The per-thread data stored is not deleted. Any data left
in QThreadStorage is leaked. Make sure that all threads using
QThreadStorage have exited before deleting the QThreadStorage.
\sa hasLocalData()
*/
/*!
\fn template <class T> bool QThreadStorage<T>::hasLocalData() const
If T is a pointer type, returns \c true if the calling thread has
non-zero data available.
If T is a value type, returns whether the data has already been
constructed by calling setLocalData or localData.
\sa localData()
*/
/*!
\fn template <class T> T &QThreadStorage<T>::localData()
Returns a reference to the data that was set by the calling
thread.
If no data has been set, this will create a default constructed
instance of type T.
\sa hasLocalData()
*/
/*!
\fn template <class T> const T QThreadStorage<T>::localData() const
\overload
Returns a copy of the data that was set by the calling thread.
\sa hasLocalData()
*/
/*!
\fn template <class T> void QThreadStorage<T>::setLocalData(T data)
Sets the local data for the calling thread to \a data. It can be
accessed later using the localData() functions.
If T is a pointer type, QThreadStorage takes ownership of the data
and deletes it automatically either when the thread exits (either
normally or via termination) or when setLocalData() is called again.
\sa localData(), hasLocalData(), clearLocalData()
*/
/*!
\fn template <class T> void QThreadStorage<T>::clearLocalData()
\since 6.13
Resets the local data (if any) for the calling thread.
If the thread had no localData(), does nothing. After the call,
hasLocalData() is \c{false} (unless the destructor of the previous value
stored a new one).
\note If \c{T} is a pointer type, this is mostly the same as
\c{setLocalData(nullptr)}. For non-pointers, this functionality was not
accessible before Qt 6.13.
This function differs from setLocalData() in that it will not create
thread-local storage when it doesn't exist for the current thread (yet, or
anymore). This makes calling the function safe in shutdown code, where
thread-local storage may already have been destroyed, and setLocalData()
would re-create it with nothing left to destroy it afterwards.
\sa setLocalData(), hasLocalData(), {qthreadstorage-shutdown-caveat}{Caveats}
*/
QT_END_NAMESPACE