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qthreadstorage.cpp

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#include "qthreadstorage.h"

#ifndef QT_NO_THREAD
#include "qthread.h"
#include "qthread_p.h"
#include "qmutex.h"

#include <string.h>

// #define THREADSTORAGE_DEBUG
#ifdef THREADSTORAGE_DEBUG
#  define DEBUG qDebug
#else
#  define DEBUG if(false)qDebug
#endif

static QBasicAtomic idCounter = Q_ATOMIC_INIT(0);
Q_GLOBAL_STATIC(QMutex, mutex)
typedef QHash<int, void (*)(void *)> DestructorHash;
Q_GLOBAL_STATIC(DestructorHash, destructors)

QThreadStorageData::QThreadStorageData(void (*func)(void *))
    : id(idCounter.fetchAndAdd(1))
{
    QMutexLocker locker(mutex());
    destructors()->insert(id, func);

    DEBUG("QThreadStorageData: Allocated id %d, destructor %p", id, func);
}

QThreadStorageData::~QThreadStorageData()
{
    QMutexLocker locker(mutex());
    if (destructors())
        destructors()->remove(id);

    DEBUG("QThreadStorageData: Released id %d", id);
}

void **QThreadStorageData::get() const
{
    QThreadData *data = QThreadData::current();
    if (!data) {
        qWarning("QThreadStorage::get: QThreadStorage can only be used with threads started with QThread");
        return 0;
    }
    QHash<int, void *>::iterator it = data->tls.find(id);
    DEBUG("QThreadStorageData: Returning storage %d, data %p, for thread %p",
          id,
          it != data->tls.end() ? it.value() : 0,
          data->thread);
    return it != data->tls.end() && it.value() != 0 ? &it.value() : 0;
}

void **QThreadStorageData::set(void *p)
{
    QThreadData *data = QThreadData::current();
    if (!data) {
        qWarning("QThreadStorage::set: QThreadStorage can only be used with threads started with QThread");
        return 0;
    }

    QHash<int, void *>::iterator it = data->tls.find(id);
    if (it != data->tls.end()) {
        // delete any previous data
        if (it.value() != 0) {
            DEBUG("QThreadStorageData: Deleting previous storage %d, data %p, for thread %p",
                  id,
                  it.value(),
                  data->thread);

            void *q = it.value();
            it.value() = 0;

            mutex()->lock();
            void (*destructor)(void *) = destructors()->value(id);
            mutex()->unlock();

            destructor(q);
        }

        // store new data
        it.value() = p;
        DEBUG("QThreadStorageData: Set storage %d for thread %p to %p", id, data->thread, p);
    } else {
        it = data->tls.insert(id, p);
        DEBUG("QThreadStorageData: Inserted storage %d, data %p, for thread %p", id, p, data->thread);
    }

    return &it.value();
}

void QThreadStorageData::finish(void **p)
{
    QHash<int, void *> *tls = reinterpret_cast<QHash<int, void *> *>(p);
    if (!tls || tls->isEmpty() || !mutex())
        return; // nothing to do

    DEBUG("QThreadStorageData: Destroying storage for thread %p", QThread::currentThread());

    QHash<int, void *>::iterator it = tls->begin();
    while (it != tls->end()) {
        int id = it.key();
        void *q = it.value();
        it.value() = 0;
        ++it;

        if (!q) {
            // data already deleted
            continue;
        }

        mutex()->lock();
        void (*destructor)(void *) = destructors()->value(id);
        mutex()->unlock();

        if (!destructor) {
            qWarning("QThreadStorage: Thread %p exited after QThreadStorage %d destroyed",
                     QThread::currentThread(), id);
            continue;
        }
        destructor(q);
    }
    tls->clear();
}

/*!
    \class QThreadStorage
    \brief The QThreadStorage class provides per-thread data storage.

    \threadsafe

    \ingroup thread
    \ingroup environment
    \mainclass

    QThreadStorage is a template class that provides per-thread data
    storage.

    \e{Note that due to compiler limitations, QThreadStorage can only
    store pointers.}

    The setLocalData() function stores a single thread-specific value
    for the calling thread. The data can be accessed later using
    localData(). 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.

    The hasLocalData() function allows the programmer to determine if
    data has previously been set using the setLocalData() function.
    This is also useful for lazy initializiation.

    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.

    \quotefromfile snippets/threads/threads.cpp
    \skipto QThreadStorage<
    \printuntil cacheObject
    \printuntil removeFromCache
    \printuntil /^\}$/

    \section1 Caveats

    \list

    \o As noted above, QThreadStorage can only store pointers due to
    compiler limitations.

    \o 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.

    \o 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 QThreadStorage::QThreadStorage()

    Constructs a new per-thread data storage object.
*/

/*!
    \fn QThreadStorage::~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 bool QThreadStorage::hasLocalData() const

    Returns true if the calling thread has non-zero data available;
    otherwise returns false.

    \sa localData()
*/

/*!
    \fn T &QThreadStorage::localData()

    Returns a reference to the data that was set by the calling
    thread.

    Note: QThreadStorage can only store pointers. This function
    returns a reference to the pointer that was set by the calling
    thread. The value of this reference is 0 if no data was set by
    the calling thread,

    \sa hasLocalData()
*/

/*!
    \fn const T QThreadStorage::localData() const
    \overload

    Returns a copy of the data that was set by the calling thread.

    Note: QThreadStorage can only store pointers. This function
    returns a pointer to the data that was set by the calling thread.
    If no data was set by the calling thread, this function returns 0.

    \sa hasLocalData()
*/

/*!
    \fn void QThreadStorage::setLocalData(T data)

    Sets the local data for the calling thread to \a data. It can be
    accessed later using the localData() functions.

    If \a data is 0, this function deletes the previous data (if
    any) and returns immediately.

    If \a data is non-zero, QThreadStorage takes ownership of the \a
    data and deletes it automatically either when the thread exits
    (either normally or via termination) or when setLocalData() is
    called again.

    Note: QThreadStorage can only store pointers. The \a data
    argument must be either a pointer to an object created on the heap
    (i.e. using \c new) or 0. You should not delete \a data
    yourself; QThreadStorage takes ownership and will delete the \a
    data itself.

    \sa localData(), hasLocalData()
*/

#endif // QT_NO_THREAD

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