Fix performance regression in QUuid::createUuid()

After commit 4363d4eebce4afd2ce3b3d6da205f8037357099a, createUuid()
would create a QFile, open it, read from it, and destroy it. This
resulted in a pretty serious performance regression (report says around
2000 times slower, I measured 3600 times slower on my machine).

This change creates one QFile per thread (since QFile is not thread
safe) and leaves the file open until the thread exits (at which point
QThreadStorage deletes the QFile).

This approach is around 600 times faster than the current code, which is
around 6 times slower than the original. Unfortunately, it is not
possible to restore the original performance without reintroducing the
problems that the commit mentioned above had fixed.

Benchmark is included.

Task-number: QTBUG-13877
Reviewed-by: thiago
Reviewed-by: mgoetz

5 files changed, 118 insertions, 26 deletions

diff --git a/src/corelib/plugin/quuid.cpp b/src/corelib/plugin/quuid.cpp
index 6c1b6e7..983d249 100644
--- a/src/corelib/plugin/quuid.cpp
+++ b/src/corelib/plugin/quuid.cpp
@@ -582,48 +582,65 @@ QT_BEGIN_INCLUDE_NAMESPACE
 #include <stdlib.h> // for RAND_MAX
 QT_END_INCLUDE_NAMESPACE
 
+#if !defined(QT_BOOTSTRAPPED) && defined(Q_OS_UNIX)
+Q_GLOBAL_STATIC(QThreadStorage<QFile *>, devUrandomStorage);
+#endif
+
 QUuid QUuid::createUuid()
 {
     QUuid result;
     uint *data = &(result.data1);
 
-#ifdef Q_OS_UNIX
-    QFile devUrandom;
-    devUrandom.setFileName(QLatin1String("/dev/urandom"));
-    if (devUrandom.open(QIODevice::ReadOnly)) {
-        qint64 numToRead = 4 * sizeof(uint);
-        devUrandom.read((char *) data, numToRead); // should read 128-bits of data
+#if defined(Q_OS_UNIX)
+    QFile *devUrandom;
+#  if !defined(QT_BOOTSTRAPPED)
+    devUrandom = devUrandomStorage()->localData();
+    if (!devUrandom) {
+        devUrandom = new QFile(QLatin1String("/dev/urandom"));
+        devUrandom->open(QIODevice::ReadOnly | QIODevice::Unbuffered);
+        devUrandomStorage()->setLocalData(devUrandom);
+    }
+# else
+    QFile file(QLatin1String("/dev/urandom"));
+    devUrandom = &file;
+    devUrandom->open(QIODevice::ReadOnly | QIODevice::Unbuffered);
+# endif
+    enum { AmountToRead = 4 * sizeof(uint) };
+    if (devUrandom->isOpen()
+        && devUrandom->read((char *) data, AmountToRead) == AmountToRead) {
+        // we got what we wanted, nothing more to do
+        ;
     } else
 #endif
     {
         static const int intbits = sizeof(int)*8;
         static int randbits = 0;
         if (!randbits) {
-        int r = 0;
+            int r = 0;
             int max = RAND_MAX;
             do { ++r; } while ((max=max>>1));
             randbits = r;
         }
 
-    // Seed the PRNG once per thread with a combination of current time, a
-    // stack address and a serial counter (since thread stack addresses are
-    // re-used).
+        // Seed the PRNG once per thread with a combination of current time, a
+        // stack address and a serial counter (since thread stack addresses are
+        // re-used).
 #ifndef QT_BOOTSTRAPPED
-    static QThreadStorage<int *> uuidseed;
-    if (!uuidseed.hasLocalData())
-    {
-        int *pseed = new int;
-        static QBasicAtomicInt serial = Q_BASIC_ATOMIC_INITIALIZER(2);
-        qsrand(*pseed = QDateTime::currentDateTime().toTime_t()
-                        + quintptr(&pseed)
-                        + serial.fetchAndAddRelaxed(1));
-        uuidseed.setLocalData(pseed);
-    }
+        static QThreadStorage<int *> uuidseed;
+        if (!uuidseed.hasLocalData())
+        {
+            int *pseed = new int;
+            static QBasicAtomicInt serial = Q_BASIC_ATOMIC_INITIALIZER(2);
+            qsrand(*pseed = QDateTime::currentDateTime().toTime_t()
+                   + quintptr(&pseed)
+                   + serial.fetchAndAddRelaxed(1));
+            uuidseed.setLocalData(pseed);
+        }
 #else
-    static bool seeded = false;
-    if (!seeded)
-        qsrand(QDateTime::currentDateTime().toTime_t()
-               + quintptr(&seeded));
+        static bool seeded = false;
+        if (!seeded)
+            qsrand(QDateTime::currentDateTime().toTime_t()
+                   + quintptr(&seeded));
 #endif
 
         int chunks = 16 / sizeof(uint);
@@ -631,7 +648,7 @@ QUuid QUuid::createUuid()
             uint randNumber = 0;
             for (int filled = 0; filled < intbits; filled += randbits)
                 randNumber |= qrand()<<filled;
-             *(data+chunks) = randNumber;
+            *(data+chunks) = randNumber;
         }
     }
 
diff --git a/tests/benchmarks/corelib/corelib.pro b/tests/benchmarks/corelib/corelib.pro
index 7669e0a..8a6941b 100644
--- a/tests/benchmarks/corelib/corelib.pro
+++ b/tests/benchmarks/corelib/corelib.pro
@@ -4,4 +4,5 @@ SUBDIRS = \
         kernel \
         thread \
         tools \
-	codecs
+	codecs \
+        plugin
diff --git a/tests/benchmarks/corelib/plugin/plugin.pro b/tests/benchmarks/corelib/plugin/plugin.pro
new file mode 100644
index 0000000..2afd7f3
--- /dev/null
+++ b/tests/benchmarks/corelib/plugin/plugin.pro
@@ -0,0 +1,2 @@
+TEMPLATE = subdirs
+SUBDIRS = quuid
diff --git a/tests/benchmarks/corelib/plugin/quuid/quuid.pro b/tests/benchmarks/corelib/plugin/quuid/quuid.pro
new file mode 100644
index 0000000..4e502fc
--- /dev/null
+++ b/tests/benchmarks/corelib/plugin/quuid/quuid.pro
@@ -0,0 +1,6 @@
+load(qttest_p4)
+TEMPLATE = app
+TARGET = tst_bench_quuid
+
+SOURCES += tst_quuid.cpp
+QT -= gui
diff --git a/tests/benchmarks/corelib/plugin/quuid/tst_quuid.cpp b/tests/benchmarks/corelib/plugin/quuid/tst_quuid.cpp
new file mode 100644
index 0000000..e9d4b44
--- /dev/null
+++ b/tests/benchmarks/corelib/plugin/quuid/tst_quuid.cpp
@@ -0,0 +1,66 @@
+/****************************************************************************
+**
+** 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 test suite 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 <QtCore/QCoreApplication>
+#include <QtCore/QUuid>
+#include <QtTest/QtTest>
+
+class tst_bench_QUuid : public QObject
+{
+    Q_OBJECT
+
+public:
+    tst_bench_QUuid()
+    { }
+
+private slots:
+    void createUuid();
+};
+
+void tst_bench_QUuid::createUuid()
+{
+    QBENCHMARK {
+        QUuid::createUuid();
+    }
+}
+
+QTEST_MAIN(tst_bench_QUuid);
+#include "tst_quuid.moc"