text: /****************************************************************************
  **
  ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
  ** Contact: http://www.qt-project.org/legal
  **
  ** This file is part of the QtCore module of the Qt Toolkit.
  **
  ** $QT_BEGIN_LICENSE:LGPL$
  ** Commercial License Usage
  ** Licensees holding valid commercial Qt licenses may use this file in
  ** accordance with the commercial license agreement provided with the
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  **
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  ** Alternatively, this file may be used under the terms of the GNU Lesser
  ** General Public License version 2.1 as published by the Free Software
  ** Foundation and appearing in the file LICENSE.LGPL included in the
  ** packaging of this file.  Please review the following information to
  ** ensure the GNU Lesser General Public License version 2.1 requirements
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  **
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  ** Alternatively, this file may be used under the terms of the GNU
  ** General Public License version 3.0 as published by the Free Software
  ** Foundation and appearing in the file LICENSE.GPL included in the
  ** packaging of this file.  Please review the following information to
  ** ensure the GNU General Public License version 3.0 requirements will be
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  ****************************************************************************/
  
  #include "qthreadstorage.h"
  
  #ifndef QT_NO_THREAD
  #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
  
  static QBasicMutex destructorsMutex;
  typedef QVector<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.count();
          DEBUG_MSG("QThreadStorageData: Allocated id %d, destructor %p cannot be stored", id, func);
          return;
      }
      for (id = 0; id < destr->count(); id++) {
          if (destr->at(id) == 0)
              break;
      }
      if (id == destr->count()) {
          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] = 0;
  }
  
  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;
      }
      QVector<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);
  
      return *v ? v : 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;
      }
      QVector<void *> &tls = data->tls;
      if (tls.size() <= id)
          tls.resize(id + 1);
  
      void *&value = tls[id];
      // delete any previous data
      if (value != 0) {
          DEBUG_MSG("QThreadStorageData: Deleting previous storage %d, data %p, for thread %p",
                  id,
                  value,
                  data->thread);
  
          QMutexLocker locker(&destructorsMutex);
          DestructorMap *destr = destructors();
          void (*destructor)(void *) = destr ? destr->value(id) : 0;
          locker.unlock();
  
          void *q = value;
          value = 0;
  
          if (destructor)
              destructor(q);
      }
  
      // store new data
      value = p;
      DEBUG_MSG("QThreadStorageData: Set storage %d for thread %p to %p", id, data->thread, p);
      return &value;
  }
  
  void QThreadStorageData::finish(void **p)
  {
      QVector<void *> *tls = reinterpret_cast<QVector<void *> *>(p);
      if (!tls || tls->isEmpty() || !destructors())
          return; // nothing to do
  
      DEBUG_MSG("QThreadStorageData: Destroying storage for thread %p", QThread::currentThread());
      while (!tls->isEmpty()) {
          void *&value = tls->last();
          void *q = value;
          value = 0;
          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 (QThread::currentThread())
                  qWarning("QThreadStorage: Thread %p exited after QThreadStorage %d destroyed",
                           QThread::currentThread(), i);
              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] = 0;
          }
      }
      tls->clear();
  }
  
  /*!
      \class QThreadStorage
      \inmodule QtCore
      \brief The QThreadStorage class provides per-thread data storage.
  
      \threadsafe
  
      \ingroup thread
  
      QThreadStorage is a template class that provides per-thread data
      storage.
  
      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 initializiation.
  
      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
  
      \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 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
  
      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 T &QThreadStorage::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 const T QThreadStorage::localData() const
      \overload
  
      Returns a copy of the data that was set by the calling thread.
  
      \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 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()
  */
  
  #endif // QT_NO_THREAD
  
  QT_END_NAMESPACE
  