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#ifndef CALL_ONCE_H
#define CALL_ONCE_H
#include <QAtomicInt>
#include <QMutex>
#include <QThread>
#include <QThreadStorage>
#include <QWaitCondition>
#include <QtGlobal>
namespace CallOnce {
enum ECallOnce { CO_Request, CO_InProgress, CO_Finished };
Q_GLOBAL_STATIC(QThreadStorage<QAtomicInt *>, once_flag)
} // namespace CallOnce
template <class Function>
inline static void qCallOnce(Function func, QBasicAtomicInt &flag) {
using namespace CallOnce;
#if QT_VERSION < 0x050000
int protectFlag = flag.fetchAndStoreAcquire(flag);
#elif QT_VERSION >= 0x050000
int protectFlag = flag.fetchAndStoreAcquire(flag.load());
#endif
if (protectFlag == CO_Finished)
return;
if (protectFlag == CO_Request &&
flag.testAndSetRelaxed(protectFlag, CO_InProgress)) {
func();
flag.fetchAndStoreRelease(CO_Finished);
} else {
do {
QThread::yieldCurrentThread();
} while (!flag.testAndSetAcquire(CO_Finished, CO_Finished));
}
}
template <class Function> inline static void qCallOncePerThread(Function func) {
using namespace CallOnce;
if (!once_flag()->hasLocalData()) {
once_flag()->setLocalData(new QAtomicInt(CO_Request));
qCallOnce(func, *once_flag()->localData());
}
}
#endif // CALL_ONCE_H