Add QFreeList as an internal class

This is a generic implementation of the lock-free free list found in
qabstracteventdispatcher.cpp. Use next() to get the next free entry in
the list, and release(id) when done with the id.

This version is templated and allows having a payload which can be
accessed using the id returned by next(). The payload is allocated and
deallocated automatically by the free list, but *NOT* when calling
next()/release(). Initialization should be done by code needing it after
next() returns. Likewise, cleanup should happen before calling
release(). It is possible to have use 'void' as the payload type, in
which case the free list only contains indexes to the next free entry.

Autotest included.

Change-Id: Ifd12a961d47f3d76593c45061f72e55c9b80a43b
Reviewed-on: http://codereview.qt.nokia.com/2160
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>

6 files changed, 544 insertions, 0 deletions

diff --git a/src/corelib/tools/qfreelist.cpp b/src/corelib/tools/qfreelist.cpp
new file mode 100644
index 0000000000..63e37ec249
--- /dev/null
+++ b/src/corelib/tools/qfreelist.cpp
@@ -0,0 +1,62 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** 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.
+**
+** 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.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qfreelist_p.h"
+
+// default sizes and offsets (no need to define these when customizing)
+enum {
+    Offset0 = 0x00000000,
+    Offset1 = 0x00008000,
+    Offset2 = 0x00080000,
+    Offset3 = 0x00800000,
+
+    Size0 = Offset1  - Offset0,
+    Size1 = Offset2  - Offset1,
+    Size2 = Offset3  - Offset2,
+    Size3 = QFreeListDefaultConstants::MaxIndex - Offset3
+};
+
+const int QFreeListDefaultConstants::Sizes[QFreeListDefaultConstants::BlockCount] = {
+    Size0,
+    Size1,
+    Size2,
+    Size3
+};
diff --git a/src/corelib/tools/qfreelist_p.h b/src/corelib/tools/qfreelist_p.h
new file mode 100644
index 0000000000..74ba3b587e
--- /dev/null
+++ b/src/corelib/tools/qfreelist_p.h
@@ -0,0 +1,294 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** 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.
+**
+** 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.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QFREELIST_P_H
+#define QFREELIST_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qatomic.h>
+
+QT_BEGIN_HEADER
+
+QT_BEGIN_NAMESPACE
+
+QT_MODULE(Core)
+
+/*! \internal
+
+    Element in a QFreeList. ConstReferenceType and ReferenceType are used as
+    the return values for QFreeList::at() and QFreeList::operator[](). Contains
+    the real data storage (_t) and the id of the next free element (next).
+
+    Note: the t() functions should be used to access the data, not _t.
+*/
+template <typename T>
+struct QFreeListElement
+{
+    typedef const T &ConstReferenceType;
+    typedef T &ReferenceType;
+
+    T _t;
+    int next;
+
+    inline ConstReferenceType t() const { return _t; }
+    inline ReferenceType t() { return _t; }
+};
+
+/*! \internal
+
+    Element in a QFreeList without a paylout. ConstReferenceType and
+    ReferenceType are void, the t() functions return void and are empty.
+*/
+template <>
+struct QFreeListElement<void>
+{
+    typedef void ConstReferenceType;
+    typedef void ReferenceType;
+
+    int next;
+
+    inline void t() const { }
+    inline void t() { }
+};
+
+/*! \internal
+
+    Defines default constants used by QFreeList:
+
+    - The initial value returned by QFreeList::next() is zero.
+
+    - QFreeList allows for up to 16777216 elements in QFreeList and uses the top
+      8 bits to store a serial counter for ABA protection.
+
+    - QFreeList will make a maximum of 4 allocations (blocks), with each
+      successive block larger than the previous.
+
+    - Sizes static int[] array to define the size of each block.
+
+    It is possible to define your own constants struct/class and give this to
+    QFreeList to customize/tune the behavior.
+*/
+struct Q_AUTOTEST_EXPORT QFreeListDefaultConstants
+{
+    // used by QFreeList, make sure to define all of when customizing
+    enum {
+        InitialNextValue = 0,
+        IndexMask = 0x00ffffff,
+        SerialMask = ~IndexMask & ~0x80000000,
+        SerialCounter = IndexMask + 1,
+        MaxIndex = IndexMask,
+        BlockCount = 4,
+    };
+
+    static const int Sizes[BlockCount];
+};
+
+/*! \internal
+
+    This is a generic implementation of a lock-free free list. Use next() to
+    get the next free entry in the list, and release(id) when done with the id.
+
+    This version is templated and allows having a payload of type T which can
+    be accessed using the id returned by next(). The payload is allocated and
+    deallocated automatically by the free list, but *NOT* when calling
+    next()/release(). Initialization should be done by code needing it after
+    next() returns. Likewise, cleanup() should happen before calling release().
+    It is possible to have use 'void' as the payload type, in which case the
+    free list only contains indexes to the next free entry.
+
+    The ConstantsType type defaults to QFreeListDefaultConstants above. You can
+    define your custom ConstantsType, see above for details on what needs to be
+    available.
+*/
+template <typename T, typename ConstantsType = QFreeListDefaultConstants>
+class QFreeList
+{
+    typedef T ValueType;
+    typedef QFreeListElement<T> ElementType;
+    typedef typename ElementType::ConstReferenceType ConstReferenceType;
+    typedef typename ElementType::ReferenceType ReferenceType;
+
+    // return which block the index \a x falls in, and modify \a x to be the index into that block
+    static inline int blockfor(int &x)
+    {
+        for (int i = 0; i < ConstantsType::BlockCount; ++i) {
+            int size = ConstantsType::Sizes[i];
+            if (x < size)
+                return i;
+            x -= size;
+        }
+        Q_ASSERT(false);
+        return -1;
+    }
+
+    // allocate a block of the given \a size, initialized starting with the given \a offset
+    static inline ElementType *allocate(int offset, int size)
+    {
+        // qDebug("QFreeList: allocating %d elements (%ld bytes) with offset %d", size, size * sizeof(ElementType), offset);
+        ElementType *v = new ElementType[size];
+        for (int i = 0; i < size; ++i)
+            v[i].next = offset + i + 1;
+        return v;
+    }
+
+    // take the current serial number from \a o, increment it, and store it in \a n
+    static inline int incrementserial(int o, int n)
+    {
+        return (n & ConstantsType::IndexMask) | ((o + ConstantsType::SerialCounter) & ConstantsType::SerialMask);
+    }
+
+    // the blocks
+    QAtomicPointer<ElementType> _v[ConstantsType::BlockCount];
+    // the next free id
+    QAtomicInt _next;
+
+    // QFreeList is not copyable
+    Q_DISABLE_COPY(QFreeList)
+
+public:
+    inline QFreeList();
+    inline ~QFreeList();
+
+    // returns the payload for the given index \a x
+    inline ConstReferenceType at(int x) const;
+    inline ReferenceType operator[](int x);
+
+    /*
+        Return the next free id. Use this id to access the payload (see above).
+        Call release(id) when done using the id.
+    */
+    inline int next();
+    inline void release(int id);
+};
+
+template <typename T, typename ConstantsType>
+inline QFreeList<T, ConstantsType>::QFreeList()
+    : _next(ConstantsType::InitialNextValue)
+{ }
+
+template <typename T, typename ConstantsType>
+inline QFreeList<T, ConstantsType>::~QFreeList()
+{
+    for (int i = 0; i < ConstantsType::BlockCount; ++i)
+        delete [] static_cast<ElementType *>(_v[i]);
+}
+
+template <typename T, typename ConstantsType>
+inline typename QFreeList<T, ConstantsType>::ConstReferenceType QFreeList<T, ConstantsType>::at(int x) const
+{
+    const int block = blockfor(x);
+    return _v[block][x].t();
+}
+
+template <typename T, typename ConstantsType>
+inline typename QFreeList<T, ConstantsType>::ReferenceType QFreeList<T, ConstantsType>::operator[](int x)
+{
+    const int block = blockfor(x);
+    return _v[block][x].t();
+}
+
+template <typename T, typename ConstantsType>
+inline int QFreeList<T, ConstantsType>::next()
+{
+    int id, newid, at;
+    ElementType *v;
+    do {
+        id = _next; // .loadAqcuire();
+
+        at = id & ConstantsType::IndexMask;
+        const int block = blockfor(at);
+        v = _v[block];
+
+        if (!v) {
+            v = allocate((id & ConstantsType::IndexMask) - at, ConstantsType::Sizes[block]);
+            if (!_v[block].testAndSetRelease(0, v)) {
+                // race with another thread lost
+                delete [] v;
+                v = _v[block];
+                Q_ASSERT(v != 0);
+            }
+        }
+
+        newid = v[at].next | (id & ~ConstantsType::IndexMask);
+    } while (!_next.testAndSetRelease(id, newid));
+    // qDebug("QFreeList::next(): returning %d (_next now %d, serial %d)",
+    //        id & ConstantsType::IndexMask,
+    //        newid & ConstantsType::IndexMask,
+    //        (newid & ~ConstantsType::IndexMask) >> 24);
+    return id & ConstantsType::IndexMask;
+}
+
+template <typename T, typename ConstantsType>
+inline void QFreeList<T, ConstantsType>::release(int id)
+{
+    int at = id & ConstantsType::IndexMask;
+    const int block = blockfor(at);
+    ElementType *v = _v[block];
+
+    int x, newid;
+    do {
+        x = _next; // .loadAcquire();
+        v[at].next = x & ConstantsType::IndexMask;
+
+        newid = incrementserial(x, id);
+    } while (!_next.testAndSetRelease(x, newid));
+    // qDebug("QFreeList::release(%d): _next now %d (was %d), serial %d",
+    //        id & ConstantsType::IndexMask,
+    //        newid & ConstantsType::IndexMask,
+    //        x & ConstantsType::IndexMask,
+    //        (newid & ~ConstantsType::IndexMask) >> 24);
+}
+
+QT_END_NAMESPACE
+
+QT_END_HEADER
+
+#endif // QFREELIST_P_H
diff --git a/src/corelib/tools/tools.pri b/src/corelib/tools/tools.pri
index f5b38eb1c0..13b597d513 100644
--- a/src/corelib/tools/tools.pri
+++ b/src/corelib/tools/tools.pri
@@ -13,6 +13,7 @@ HEADERS +=  \
         tools/qdatetime.h \
         tools/qdatetime_p.h \
         tools/qeasingcurve.h \
+        tools/qfreelist_p.h \
         tools/qhash.h \
         tools/qline.h \
         tools/qlinkedlist.h \
@@ -61,6 +62,7 @@ SOURCES += \
         tools/qdatetime.cpp \
         tools/qeasingcurve.cpp \
         tools/qelapsedtimer.cpp \
+        tools/qfreelist.cpp \
         tools/qhash.cpp \
         tools/qline.cpp \
         tools/qlinkedlist.cpp \
diff --git a/tests/auto/corelib.pro b/tests/auto/corelib.pro
index 95a16f67d9..7a655d6208 100644
--- a/tests/auto/corelib.pro
+++ b/tests/auto/corelib.pro
@@ -30,6 +30,7 @@ SUBDIRS=\
    qfileinfo \
    qfilesystemwatcher \
    qflags \
+   qfreelist \
    qfuture \
    qfuturewatcher \
    qgetputenv \
diff --git a/tests/auto/qfreelist/qfreelist.pro b/tests/auto/qfreelist/qfreelist.pro
new file mode 100644
index 0000000000..b7f2b3d38f
--- /dev/null
+++ b/tests/auto/qfreelist/qfreelist.pro
@@ -0,0 +1,6 @@
+load(qttest_p4)
+SOURCES  += tst_qfreelist.cpp
+QT += core-private
+QT -= gui
+
+!private_tests:SOURCES += $$QT_SOURCE_TREE/src/corelib/tools/qfreelist.cpp
diff --git a/tests/auto/qfreelist/tst_qfreelist.cpp b/tests/auto/qfreelist/tst_qfreelist.cpp
new file mode 100644
index 0000000000..139d76e64a
--- /dev/null
+++ b/tests/auto/qfreelist/tst_qfreelist.cpp
@@ -0,0 +1,179 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** 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.
+**
+** 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.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+
+#include <QtCore/QCoreApplication>
+#include <QtCore/QElapsedTimer>
+#include <QtCore/QList>
+#include <QtCore/QThread>
+#include <private/qfreelist_p.h>
+#include <QtTest/QtTest>
+
+//TESTED_CLASS=QFreeList
+//TESTED_FILES=corelib/tools/qfreelist_p.h
+
+class tst_QFreeList : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void basicTest();
+    void customized();
+    void threadedTest();
+};
+
+void tst_QFreeList::basicTest()
+{
+    {
+        QFreeList<void> voidFreeList;
+        int zero = voidFreeList.next();
+        int one  = voidFreeList.next();
+        int two = voidFreeList.next();
+        QCOMPARE(zero, 0);
+        QCOMPARE(one, 1);
+        QCOMPARE(two, 2);
+        voidFreeList[zero];
+        voidFreeList[one];
+        voidFreeList[two];
+        voidFreeList.at(zero);
+        voidFreeList.at(one);
+        voidFreeList.at(two);
+        voidFreeList.release(one);
+        int next = voidFreeList.next();
+        QCOMPARE(next, 1);
+        voidFreeList[next];
+        voidFreeList.at(next);
+    }
+
+    {
+        QFreeList<int> intFreeList;
+        int zero = intFreeList.next();
+        int one = intFreeList.next();
+        int two = intFreeList.next();
+        QCOMPARE(zero, 0);
+        QCOMPARE(one, 1);
+        QCOMPARE(two, 2);
+        intFreeList[zero] = zero;
+        intFreeList[one] = one;
+        intFreeList[two] = two;
+        QCOMPARE(intFreeList.at(zero), zero);
+        QCOMPARE(intFreeList.at(one), one);
+        QCOMPARE(intFreeList.at(two), two);
+        intFreeList.release(one);
+        int next = intFreeList.next();
+        QCOMPARE(next, 1);
+        QCOMPARE(intFreeList.at(next), one);
+        intFreeList[next] = -one;
+        QCOMPARE(intFreeList.at(next), -one);
+    }
+}
+
+struct CustomFreeListConstants : public QFreeListDefaultConstants
+{
+    enum {
+        InitialNextValue = 50,
+        BlockCount = 10
+    };
+
+    static const int Sizes[10];
+};
+
+const int CustomFreeListConstants::Sizes[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 16777216 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 };
+
+void tst_QFreeList::customized()
+{
+    QFreeList<void, CustomFreeListConstants> customFreeList;
+    int next = customFreeList.next();
+    QCOMPARE(next, int(CustomFreeListConstants::InitialNextValue));
+    customFreeList[next];
+    customFreeList.at(next);
+    customFreeList.release(next);
+}
+
+enum { TimeLimit = 3000 };
+
+class FreeListThread : public QThread
+{
+    static QFreeList<void> freelist;
+
+public:
+    inline FreeListThread() : QThread() { }
+    inline void run()
+    {
+        QElapsedTimer t;
+        t.start();
+        QList<int> needToRelease;
+        do {
+            int i = freelist.next();
+            int j = freelist.next();
+            int k = freelist.next();
+            int l = freelist.next();
+            freelist.release(k);
+            int n = freelist.next();
+            int m = freelist.next();
+            freelist.release(l);
+            freelist.release(m);
+            freelist.release(n);
+            freelist.release(j);
+            // freelist.release(i);
+            needToRelease << i;
+        } while (t.elapsed() < TimeLimit);
+
+        foreach (int x, needToRelease)
+            freelist.release(x);
+    }
+};
+
+QFreeList<void> FreeListThread::freelist;
+
+void tst_QFreeList::threadedTest()
+{
+    const int ThreadCount = QThread::idealThreadCount();
+    FreeListThread *threads = new FreeListThread[ThreadCount];
+    for (int i = 0; i < ThreadCount; ++i)
+        threads[i].start();
+    for (int i = 0; i < ThreadCount; ++i)
+        threads[i].wait();
+    delete [] threads;
+}
+
+QTEST_MAIN(tst_QFreeList)
+#include "tst_qfreelist.moc"