summaryrefslogtreecommitdiffstats
path: root/src/concurrent/qtconcurrentiteratekernel.h
blob: 5d899b5ca68f69cfe12da3c56e51ec106e02b4cb (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
/****************************************************************************
**
** Copyright (C) 2012 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
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Digia.  For licensing terms and
** conditions see http://qt.digia.com/licensing.  For further information
** use the contact form at http://qt.digia.com/contact-us.
**
** 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, Digia gives you certain additional
** rights.  These rights are described in the Digia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** 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
** met: http://www.gnu.org/copyleft/gpl.html.
**
**
** $QT_END_LICENSE$
**
****************************************************************************/

#ifndef QTCONCURRENT_ITERATEKERNEL_H
#define QTCONCURRENT_ITERATEKERNEL_H

#include <QtConcurrent/qtconcurrent_global.h>

#ifndef QT_NO_CONCURRENT

#include <QtCore/qatomic.h>
#include <QtConcurrent/qtconcurrentmedian.h>
#include <QtConcurrent/qtconcurrentthreadengine.h>

#include <iterator>

QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE


#ifndef qdoc

namespace QtConcurrent {

    using std::advance;

/*
    The BlockSizeManager class manages how many iterations a thread should
    reserve and process at a time. This is done by measuring the time spent
    in the user code versus the control part code, and then increasing
    the block size if the ratio between them is to small. The block size
    management is done on the basis of the median of several timing measuremens,
    and it is done induvidualy for each thread.
*/
class Q_CONCURRENT_EXPORT BlockSizeManager
{
public:
    BlockSizeManager(int iterationCount);
    void timeBeforeUser();
    void timeAfterUser();
    int blockSize();
private:
    inline bool blockSizeMaxed()
    {
        return (m_blockSize >= maxBlockSize);
    }

    const int maxBlockSize;
    qint64 beforeUser;
    qint64 afterUser;
    Median<double> controlPartElapsed;
    Median<double> userPartElapsed;
    int m_blockSize;
};

template <typename T>
class ResultReporter
{
public:
    ResultReporter(ThreadEngine<T> *_threadEngine)
    :threadEngine(_threadEngine)
    {

    }

    void reserveSpace(int resultCount)
    {
        currentResultCount = resultCount;
        vector.resize(qMax(resultCount, vector.count()));
    }

    void reportResults(int begin)
    {
        const int useVectorThreshold = 4; // Tunable parameter.
        if (currentResultCount > useVectorThreshold) {
            vector.resize(currentResultCount);
            threadEngine->reportResults(vector, begin);
        } else {
            for (int i = 0; i < currentResultCount; ++i)
                threadEngine->reportResult(&vector.at(i), begin + i);
        }
    }

    inline T * getPointer()
    {
        return vector.data();
    }

    int currentResultCount;
    ThreadEngine<T> *threadEngine;
    QVector<T> vector;
};

template <>
class ResultReporter<void>
{
public:
    inline ResultReporter(ThreadEngine<void> *) { }
    inline void reserveSpace(int) { }
    inline void reportResults(int) { }
    inline void * getPointer() { return 0; }
};

inline bool selectIteration(std::bidirectional_iterator_tag)
{
    return false; // while
}

inline bool selectIteration(std::forward_iterator_tag)
{
    return false; // while
}

inline bool selectIteration(std::random_access_iterator_tag)
{
    return true; // for
}

template <typename Iterator, typename T>
class IterateKernel : public ThreadEngine<T>
{
public:
    typedef T ResultType;

    IterateKernel(Iterator _begin, Iterator _end)
        : begin(_begin), end(_end), current(_begin), currentIndex(0),
           forIteration(selectIteration(typename std::iterator_traits<Iterator>::iterator_category())), progressReportingEnabled(true)
    {
        iterationCount =  forIteration ? std::distance(_begin, _end) : 0;
    }

    virtual ~IterateKernel() { }

    virtual bool runIteration(Iterator it, int index , T *result)
        { Q_UNUSED(it); Q_UNUSED(index); Q_UNUSED(result); return false; }
    virtual bool runIterations(Iterator _begin, int beginIndex, int endIndex, T *results)
        { Q_UNUSED(_begin); Q_UNUSED(beginIndex); Q_UNUSED(endIndex); Q_UNUSED(results); return false; }

    void start()
    {
        progressReportingEnabled = this->isProgressReportingEnabled();
        if (progressReportingEnabled && iterationCount > 0)
            this->setProgressRange(0, iterationCount);
    }

    bool shouldStartThread()
    {
        if (forIteration)
            return (currentIndex.load() < iterationCount) && !this->shouldThrottleThread();
        else // whileIteration
            return (iteratorThreads.load() == 0);
    }

    ThreadFunctionResult threadFunction()
    {
        if (forIteration)
            return this->forThreadFunction();
        else // whileIteration
            return this->whileThreadFunction();
    }

    ThreadFunctionResult forThreadFunction()
    {
        BlockSizeManager blockSizeManager(iterationCount);
        ResultReporter<T> resultReporter(this);

        for(;;) {
            if (this->isCanceled())
                break;

            const int currentBlockSize = blockSizeManager.blockSize();

            if (currentIndex.load() >= iterationCount)
                break;

            // Atomically reserve a block of iterationCount for this thread.
            const int beginIndex = currentIndex.fetchAndAddRelease(currentBlockSize);
            const int endIndex = qMin(beginIndex + currentBlockSize, iterationCount);

            if (beginIndex >= endIndex) {
                // No more work
                break;
            }

            this->waitForResume(); // (only waits if the qfuture is paused.)

            if (shouldStartThread())
                this->startThread();

            const int finalBlockSize = endIndex - beginIndex; // block size adjusted for possible end-of-range
            resultReporter.reserveSpace(finalBlockSize);

            // Call user code with the current iteration range.
            blockSizeManager.timeBeforeUser();
            const bool resultsAvailable = this->runIterations(begin, beginIndex, endIndex, resultReporter.getPointer());
            blockSizeManager.timeAfterUser();

            if (resultsAvailable)
                resultReporter.reportResults(beginIndex);

            // Report progress if progress reporting enabled.
            if (progressReportingEnabled) {
                completed.fetchAndAddAcquire(finalBlockSize);
                this->setProgressValue(this->completed.load());
            }

            if (this->shouldThrottleThread())
                return ThrottleThread;
        }
        return ThreadFinished;
    }

    ThreadFunctionResult whileThreadFunction()
    {
        if (iteratorThreads.testAndSetAcquire(0, 1) == false)
            return ThreadFinished;

        ResultReporter<T> resultReporter(this);
        resultReporter.reserveSpace(1);

        while (current != end) {
            // The following two lines breaks support for input iterators according to
            // the sgi docs: dereferencing prev after calling ++current is not allowed
            // on input iterators. (prev is dereferenced inside user.runIteration())
            Iterator prev = current;
            ++current;
            int index = currentIndex.fetchAndAddRelaxed(1);
            iteratorThreads.testAndSetRelease(1, 0);

            this->waitForResume(); // (only waits if the qfuture is paused.)

            if (shouldStartThread())
                this->startThread();

            const bool resultAavailable = this->runIteration(prev, index, resultReporter.getPointer());
            if (resultAavailable)
                resultReporter.reportResults(index);

            if (this->shouldThrottleThread())
                return ThrottleThread;

            if (iteratorThreads.testAndSetAcquire(0, 1) == false)
                return ThreadFinished;
        }

        return ThreadFinished;
    }


public:
    const Iterator begin;
    const Iterator end;
    Iterator current;
    QAtomicInt currentIndex;
    bool forIteration;
    QAtomicInt iteratorThreads;
    int iterationCount;

    bool progressReportingEnabled;
    QAtomicInt completed;
};

} // namespace QtConcurrent

#endif //qdoc

QT_END_NAMESPACE
QT_END_HEADER

#endif // QT_NO_CONCURRENT

#endif