summaryrefslogtreecommitdiffstats
path: root/src/network/kernel/qhostinfo.cpp
blob: 8ae1305266bf4b2f1e03e1049c17c79d6529e7e4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtNetwork module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Lesser General Public License Usage
** 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
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights.  These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
**
**
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "qhostinfo.h"
#include "qhostinfo_p.h"

#include "QtCore/qscopedpointer.h"
#include <qabstracteventdispatcher.h>
#include <qcoreapplication.h>
#include <qmetaobject.h>
#include <qstringlist.h>
#include <qthread.h>
#include <qurl.h>

#ifdef Q_OS_UNIX
#  include <unistd.h>
#endif

QT_BEGIN_NAMESPACE

#ifndef QT_NO_THREAD
Q_GLOBAL_STATIC(QHostInfoLookupManager, theHostInfoLookupManager)
#endif

//#define QHOSTINFO_DEBUG

/*!
    \class QHostInfo
    \brief The QHostInfo class provides static functions for host name lookups.

    \reentrant
    \inmodule QtNetwork
    \ingroup network

    QHostInfo uses the lookup mechanisms provided by the operating
    system to find the IP address(es) associated with a host name,
    or the host name associated with an IP address.
    The class provides two static convenience functions: one that
    works asynchronously and emits a signal once the host is found,
    and one that blocks and returns a QHostInfo object.

    To look up a host's IP addresses asynchronously, call lookupHost(),
    which takes the host name or IP address, a receiver object, and a slot
    signature as arguments and returns an ID. You can abort the
    lookup by calling abortHostLookup() with the lookup ID.

    Example:

    \snippet doc/src/snippets/code/src_network_kernel_qhostinfo.cpp 0


    The slot is invoked when the results are ready. (If you use
    Qt for Embedded Linux and disabled multithreading support by defining
    \c QT_NO_THREAD, lookupHost() will block until the lookup has
    finished.) The results are stored in a QHostInfo object. Call
    addresses() to get the list of IP addresses for the host, and
    hostName() to get the host name that was looked up.

    If the lookup failed, error() returns the type of error that
    occurred. errorString() gives a human-readable description of the
    lookup error.

    If you want a blocking lookup, use the QHostInfo::fromName() function:

    \snippet doc/src/snippets/code/src_network_kernel_qhostinfo.cpp 1

    QHostInfo supports Internationalized Domain Names (IDNs) through the
    IDNA and Punycode standards.

    To retrieve the name of the local host, use the static
    QHostInfo::localHostName() function.

    \note Since Qt 4.6.1 QHostInfo is using multiple threads for DNS lookup
    instead of one dedicated DNS thread. This improves performance,
    but also changes the order of signal emissions when using lookupHost()
    compared to previous versions of Qt.
    \note Since Qt 4.6.3 QHostInfo is using a small internal 60 second DNS cache
    for performance improvements.

    \sa QAbstractSocket, {http://www.rfc-editor.org/rfc/rfc3492.txt}{RFC 3492}
*/

static QBasicAtomicInt theIdCounter = Q_BASIC_ATOMIC_INITIALIZER(1);

/*!
    Looks up the IP address(es) associated with host name \a name, and
    returns an ID for the lookup. When the result of the lookup is
    ready, the slot or signal \a member in \a receiver is called with
    a QHostInfo argument. The QHostInfo object can then be inspected
    to get the results of the lookup.

    The lookup is performed by a single function call, for example:

    \snippet doc/src/snippets/code/src_network_kernel_qhostinfo.cpp 2

    The implementation of the slot prints basic information about the
    addresses returned by the lookup, or reports an error if it failed:

    \snippet doc/src/snippets/code/src_network_kernel_qhostinfo.cpp 3

    If you pass a literal IP address to \a name instead of a host name,
    QHostInfo will search for the domain name for the IP (i.e., QHostInfo will
    perform a \e reverse lookup). On success, the resulting QHostInfo will
    contain both the resolved domain name and IP addresses for the host
    name. Example:

    \snippet doc/src/snippets/code/src_network_kernel_qhostinfo.cpp 4

    \note There is no guarantee on the order the signals will be emitted
    if you start multiple requests with lookupHost().

    \sa abortHostLookup(), addresses(), error(), fromName()
*/
int QHostInfo::lookupHost(const QString &name, QObject *receiver,
                          const char *member)
{
#if defined QHOSTINFO_DEBUG
    qDebug("QHostInfo::lookupHost(\"%s\", %p, %s)",
           name.toLatin1().constData(), receiver, member ? member + 1 : 0);
#endif
    if (!QAbstractEventDispatcher::instance(QThread::currentThread())) {
        qWarning("QHostInfo::lookupHost() called with no event dispatcher");
        return -1;
    }

    qRegisterMetaType<QHostInfo>("QHostInfo");

    int id = theIdCounter.fetchAndAddRelaxed(1); // generate unique ID

    if (name.isEmpty()) {
        QHostInfo hostInfo(id);
        hostInfo.setError(QHostInfo::HostNotFound);
        hostInfo.setErrorString(QCoreApplication::translate("QHostInfo", "No host name given"));
        QScopedPointer<QHostInfoResult> result(new QHostInfoResult);
        QObject::connect(result.data(), SIGNAL(resultsReady(QHostInfo)),
                         receiver, member, Qt::QueuedConnection);
        result.data()->emitResultsReady(hostInfo);
        return id;
    }

#ifdef QT_NO_THREAD
    QHostInfo hostInfo = QHostInfoAgent::fromName(name);
    hostInfo.setLookupId(id);
    QScopedPointer<QHostInfoResult> result(new QHostInfoResult);
    QObject::connect(result.data(), SIGNAL(resultsReady(QHostInfo)),
                     receiver, member, Qt::QueuedConnection);
    result.data()->emitResultsReady(hostInfo);
#else
    QHostInfoLookupManager *manager = theHostInfoLookupManager();
    if (manager) {
        // the application is still alive
        if (manager->cache.isEnabled()) {
            // check cache first
            bool valid = false;
            QHostInfo info = manager->cache.get(name, &valid);
            if (valid) {
                info.setLookupId(id);
                QHostInfoResult result;
                QObject::connect(&result, SIGNAL(resultsReady(QHostInfo)), receiver, member, Qt::QueuedConnection);
                result.emitResultsReady(info);
                return id;
            }
        }
        // cache is not enabled or it was not in the cache, do normal lookup
        QHostInfoRunnable* runnable = new QHostInfoRunnable(name, id);
        QObject::connect(&runnable->resultEmitter, SIGNAL(resultsReady(QHostInfo)), receiver, member, Qt::QueuedConnection);
        manager->scheduleLookup(runnable);
    }
#endif

    return id;
}

/*!
    Aborts the host lookup with the ID \a id, as returned by lookupHost().

    \sa lookupHost(), lookupId()
*/
void QHostInfo::abortHostLookup(int id)
{
#ifndef QT_NO_THREAD
    theHostInfoLookupManager()->abortLookup(id);
#else
    // we cannot abort if it was non threaded.. the result signal has already been posted
    Q_UNUSED(id);
#endif
}

/*!
    Looks up the IP address(es) for the given host \a name. The
    function blocks during the lookup which means that execution of
    the program is suspended until the results of the lookup are
    ready. Returns the result of the lookup in a QHostInfo object.

    If you pass a literal IP address to \a name instead of a host name,
    QHostInfo will search for the domain name for the IP (i.e., QHostInfo will
    perform a \e reverse lookup). On success, the returned QHostInfo will
    contain both the resolved domain name and IP addresses for the host name.

    \sa lookupHost()
*/
QHostInfo QHostInfo::fromName(const QString &name)
{
#if defined QHOSTINFO_DEBUG
    qDebug("QHostInfo::fromName(\"%s\")",name.toLatin1().constData());
#endif

    return QHostInfoAgent::fromName(name);
}

/*!
    \enum QHostInfo::HostInfoError

    This enum describes the various errors that can occur when trying
    to resolve a host name.

    \value NoError The lookup was successful.
    \value HostNotFound No IP addresses were found for the host.
    \value UnknownError An unknown error occurred.

    \sa error(), setError()
*/

/*!
    Constructs an empty host info object with lookup ID \a id.

    \sa lookupId()
*/
QHostInfo::QHostInfo(int id)
    : d(new QHostInfoPrivate)
{
    d->lookupId = id;
}

/*!
    Constructs a copy of \a other.
*/
QHostInfo::QHostInfo(const QHostInfo &other)
    : d(new QHostInfoPrivate(*other.d.data()))
{
}

/*!
    Assigns the data of the \a other object to this host info object,
    and returns a reference to it.
*/
QHostInfo &QHostInfo::operator=(const QHostInfo &other)
{
    *d.data() = *other.d.data();
    return *this;
}

/*!
    Destroys the host info object.
*/
QHostInfo::~QHostInfo()
{
}

/*!
    Returns the list of IP addresses associated with hostName(). This
    list may be empty.

    Example:

    \snippet doc/src/snippets/code/src_network_kernel_qhostinfo.cpp 5

    \sa hostName(), error()
*/
QList<QHostAddress> QHostInfo::addresses() const
{
    return d->addrs;
}

/*!
    Sets the list of addresses in this QHostInfo to \a addresses.

    \sa addresses()
*/
void QHostInfo::setAddresses(const QList<QHostAddress> &addresses)
{
    d->addrs = addresses;
}

/*!
    Returns the name of the host whose IP addresses were looked up.

    \sa localHostName()
*/
QString QHostInfo::hostName() const
{
    return d->hostName;
}

/*!
    Sets the host name of this QHostInfo to \a hostName.

    \sa hostName()
*/
void QHostInfo::setHostName(const QString &hostName)
{
    d->hostName = hostName;
}

/*!
    Returns the type of error that occurred if the host name lookup
    failed; otherwise returns NoError.

    \sa setError(), errorString()
*/
QHostInfo::HostInfoError QHostInfo::error() const
{
    return d->err;
}

/*!
    Sets the error type of this QHostInfo to \a error.

    \sa error(), errorString()
*/
void QHostInfo::setError(HostInfoError error)
{
    d->err = error;
}

/*!
    Returns the ID of this lookup.

    \sa setLookupId(), abortHostLookup(), hostName()
*/
int QHostInfo::lookupId() const
{
    return d->lookupId;
}

/*!
    Sets the ID of this lookup to \a id.

    \sa lookupId(), lookupHost()
*/
void QHostInfo::setLookupId(int id)
{
    d->lookupId = id;
}

/*!
    If the lookup failed, this function returns a human readable
    description of the error; otherwise "Unknown error" is returned.

    \sa setErrorString(), error()
*/
QString QHostInfo::errorString() const
{
    return d->errorStr;
}

/*!
    Sets the human readable description of the error that occurred to \a str
    if the lookup failed.

    \sa errorString(), setError()
*/
void QHostInfo::setErrorString(const QString &str)
{
    d->errorStr = str;
}

/*!
    \fn QString QHostInfo::localHostName()

    Returns the host name of this machine.

    \sa hostName()
*/

/*!
    \fn QString QHostInfo::localDomainName()

    Returns the DNS domain of this machine.

    Note: DNS domains are not related to domain names found in
    Windows networks.

    \sa hostName()
*/

#ifndef QT_NO_THREAD
QHostInfoRunnable::QHostInfoRunnable(QString hn, int i) : toBeLookedUp(hn), id(i)
{
    setAutoDelete(true);
}

// the QHostInfoLookupManager will at some point call this via a QThreadPool
void QHostInfoRunnable::run()
{
    QHostInfoLookupManager *manager = theHostInfoLookupManager();
    // check aborted
    if (manager->wasAborted(id)) {
        manager->lookupFinished(this);
        return;
    }

    QHostInfo hostInfo;

    // QHostInfo::lookupHost already checks the cache. However we need to check
    // it here too because it might have been cache saved by another QHostInfoRunnable
    // in the meanwhile while this QHostInfoRunnable was scheduled but not running
    if (manager->cache.isEnabled()) {
        // check the cache first
        bool valid = false;
        hostInfo = manager->cache.get(toBeLookedUp, &valid);
        if (!valid) {
            // not in cache, we need to do the lookup and store the result in the cache
            hostInfo = QHostInfoAgent::fromName(toBeLookedUp);
            manager->cache.put(toBeLookedUp, hostInfo);
        }
    } else {
        // cache is not enabled, just do the lookup and continue
        hostInfo = QHostInfoAgent::fromName(toBeLookedUp);
    }

    // check aborted again
    if (manager->wasAborted(id)) {
        manager->lookupFinished(this);
        return;
    }

    // signal emission
    hostInfo.setLookupId(id);
    resultEmitter.emitResultsReady(hostInfo);

    // now also iterate through the postponed ones
    QMutableListIterator<QHostInfoRunnable*> iterator(manager->postponedLookups);
    while (iterator.hasNext()) {
        QHostInfoRunnable* postponed = iterator.next();
        if (toBeLookedUp == postponed->toBeLookedUp) {
            // we can now emit
            iterator.remove();
            hostInfo.setLookupId(postponed->id);
            postponed->resultEmitter.emitResultsReady(hostInfo);
        }
    }

    manager->lookupFinished(this);

    // thread goes back to QThreadPool
}

QHostInfoLookupManager::QHostInfoLookupManager() : mutex(QMutex::Recursive), wasDeleted(false)
{
    moveToThread(QCoreApplicationPrivate::mainThread());
    connect(QCoreApplication::instance(), SIGNAL(destroyed()), SLOT(waitForThreadPoolDone()), Qt::DirectConnection);
    threadPool.setMaxThreadCount(5); // do 5 DNS lookups in parallel
}

QHostInfoLookupManager::~QHostInfoLookupManager()
{
    wasDeleted = true;

    // don't qDeleteAll currentLookups, the QThreadPool has ownership
    clear();
}

void QHostInfoLookupManager::clear()
{
    {
        QMutexLocker locker(&mutex);
        qDeleteAll(postponedLookups);
        qDeleteAll(scheduledLookups);
        qDeleteAll(finishedLookups);
        postponedLookups.clear();
        scheduledLookups.clear();
        finishedLookups.clear();
    }

    threadPool.waitForDone();
    cache.clear();
}

void QHostInfoLookupManager::work()
{
    if (wasDeleted)
        return;

    // goals of this function:
    //  - launch new lookups via the thread pool
    //  - make sure only one lookup per host/IP is in progress

    QMutexLocker locker(&mutex);

    if (!finishedLookups.isEmpty()) {
        // remove ID from aborted if it is in there
        for (int i = 0; i < finishedLookups.length(); i++) {
           abortedLookups.removeAll(finishedLookups.at(i)->id);
        }

        finishedLookups.clear();
    }

    if (!postponedLookups.isEmpty()) {
        // try to start the postponed ones

        QMutableListIterator<QHostInfoRunnable*> iterator(postponedLookups);
        while (iterator.hasNext()) {
            QHostInfoRunnable* postponed = iterator.next();

            // check if none of the postponed hostnames is currently running
            bool alreadyRunning = false;
            for (int i = 0; i < currentLookups.length(); i++) {
                if (currentLookups.at(i)->toBeLookedUp == postponed->toBeLookedUp) {
                    alreadyRunning = true;
                    break;
                }
            }
            if (!alreadyRunning) {
                iterator.remove();
                scheduledLookups.prepend(postponed); // prepend! we want to finish it ASAP
            }
        }
    }

    if (!scheduledLookups.isEmpty()) {
        // try to start the new ones
        QMutableListIterator<QHostInfoRunnable*> iterator(scheduledLookups);
        while (iterator.hasNext()) {
            QHostInfoRunnable *scheduled = iterator.next();

            // check if a lookup for this host is already running, then postpone
            for (int i = 0; i < currentLookups.size(); i++) {
                if (currentLookups.at(i)->toBeLookedUp == scheduled->toBeLookedUp) {
                    iterator.remove();
                    postponedLookups.append(scheduled);
                    scheduled = 0;
                    break;
                }
            }

            if (scheduled && currentLookups.size() < threadPool.maxThreadCount()) {
                // runnable now running in new thread, track this in currentLookups
                threadPool.start(scheduled);
                iterator.remove();
                currentLookups.append(scheduled);
            } else {
                // was postponed, continue iterating
                continue;
            }
        };
    }
}

// called by QHostInfo
void QHostInfoLookupManager::scheduleLookup(QHostInfoRunnable *r)
{
    if (wasDeleted)
        return;

    QMutexLocker locker(&this->mutex);
    scheduledLookups.enqueue(r);
    work();
}

// called by QHostInfo
void QHostInfoLookupManager::abortLookup(int id)
{
    if (wasDeleted)
        return;

    QMutexLocker locker(&this->mutex);

    // is postponed? delete and return
    for (int i = 0; i < postponedLookups.length(); i++) {
        if (postponedLookups.at(i)->id == id) {
            delete postponedLookups.takeAt(i);
            return;
        }
    }

    // is scheduled? delete and return
    for (int i = 0; i < scheduledLookups.length(); i++) {
        if (scheduledLookups.at(i)->id == id) {
            delete scheduledLookups.takeAt(i);
            return;
        }
    }

    if (!abortedLookups.contains(id))
        abortedLookups.append(id);
}

// called from QHostInfoRunnable
bool QHostInfoLookupManager::wasAborted(int id)
{
    if (wasDeleted)
        return true;

    QMutexLocker locker(&this->mutex);
    return abortedLookups.contains(id);
}

// called from QHostInfoRunnable
void QHostInfoLookupManager::lookupFinished(QHostInfoRunnable *r)
{
    if (wasDeleted)
        return;

    QMutexLocker locker(&this->mutex);
    currentLookups.removeOne(r);
    finishedLookups.append(r);
    work();
}

// This function returns immediatly when we had a result in the cache, else it will later emit a signal
QHostInfo qt_qhostinfo_lookup(const QString &name, QObject *receiver, const char *member, bool *valid, int *id)
{
    *valid = false;
    *id = -1;

    // check cache
    QHostInfoLookupManager* manager = theHostInfoLookupManager();
    if (manager && manager->cache.isEnabled()) {
        QHostInfo info = manager->cache.get(name, valid);
        if (*valid) {
            return info;
        }
    }

    // was not in cache, trigger lookup
    *id = QHostInfo::lookupHost(name, receiver, member);

    // return empty response, valid==false
    return QHostInfo();
}

void qt_qhostinfo_clear_cache()
{
    QHostInfoLookupManager* manager = theHostInfoLookupManager();
    if (manager) {
        manager->clear();
    }
}

void Q_AUTOTEST_EXPORT qt_qhostinfo_enable_cache(bool e)
{
    QHostInfoLookupManager* manager = theHostInfoLookupManager();
    if (manager) {
        manager->cache.setEnabled(e);
    }
}

// cache for 60 seconds
// cache 64 items
QHostInfoCache::QHostInfoCache() : max_age(60), enabled(true), cache(64)
{
#ifdef QT_QHOSTINFO_CACHE_DISABLED_BY_DEFAULT
    enabled = false;
#endif
}

bool QHostInfoCache::isEnabled()
{
    return enabled;
}

// this function is currently only used for the auto tests
// and not usable by public API
void QHostInfoCache::setEnabled(bool e)
{
    enabled = e;
}


QHostInfo QHostInfoCache::get(const QString &name, bool *valid)
{
    QMutexLocker locker(&this->mutex);

    *valid = false;
    if (cache.contains(name)) {
        QHostInfoCacheElement *element = cache.object(name);
        if (element->age.elapsed() < max_age*1000)
            *valid = true;
        return element->info;

        // FIXME idea:
        // if too old but not expired, trigger a new lookup
        // to freshen our cache
    }

    return QHostInfo();
}

void QHostInfoCache::put(const QString &name, const QHostInfo &info)
{
    // if the lookup failed, don't cache
    if (info.error() != QHostInfo::NoError)
        return;

    QHostInfoCacheElement* element = new QHostInfoCacheElement();
    element->info = info;
    element->age = QTime();
    element->age.start();

    QMutexLocker locker(&this->mutex);
    cache.insert(name, element); // cache will take ownership
}

void QHostInfoCache::clear()
{
    QMutexLocker locker(&this->mutex);
    cache.clear();
}

#endif // QT_NO_THREAD

QT_END_NAMESPACE