2 files changed, 37 insertions, 4 deletions
diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index 742f4ec..9fc3c8d 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -46,6 +46,7 @@
 #include "qthreadstorage.h"
 #include "qdir.h"
 #include "qstringlist.h"
+#include "qdatetime.h"
 
 #ifndef QT_NO_QOBJECT
 #include <private/qthread_p.h>
@@ -2523,6 +2524,33 @@ void qsrand(uint seed)
 #endif
 }
 
+/*! \internal
+    \relates <QtGlobal>
+    \since 4.6
+
+    Seed the PRNG, but only if it has not already been seeded.
+
+    The default seed is a combination of current time, a stack address and a
+    serial counter (since thread stack addresses are re-used).
+*/
+void qsrand()
+{
+#if defined(Q_OS_UNIX) && !defined(QT_NO_THREAD) && !defined(Q_OS_SYMBIAN)
+    SeedStorageType *pseed = randTLS()->localData();
+    if (pseed) {
+        // already seeded
+        return;
+    }
+    randTLS()->setLocalData(pseed = new SeedStorageType);
+    static QBasicAtomicInt serial = Q_BASIC_ATOMIC_INITIALIZER(0);
+    *pseed = QDateTime::currentDateTime().toTime_t()
+             + quintptr(&pseed)
+             + serial.fetchAndAddRelaxed(1);
+#else
+    // On Windows, we assume that rand() already does the right thing
+#endif
+}
+
 /*!
     \relates <QtGlobal>
     \since 4.2
diff --git a/src/corelib/plugin/quuid.cpp b/src/corelib/plugin/quuid.cpp
index 7224ad3..3c79653 100644
--- a/src/corelib/plugin/quuid.cpp
+++ b/src/corelib/plugin/quuid.cpp
@@ -548,9 +548,11 @@ bool QUuid::operator>(const QUuid &other) const
     On any platform other than Windows, this function returns a new
     UUID with variant QUuid::DCE and version QUuid::Random. The random
     numbers used to construct the UUID are obtained from the local
-    pseudo-random generator, which is usually not a cryptographic
+    pseudo-random generator, qrand(), which is usually not a cryptographic
     quality random number generator. Therefore, a UUID generated by
-    this function can't be guaranteed to be unique.
+    this function can't be guaranteed to be unique. If the pseudo-random
+    number generator for the calling thread has not yet been seeded, this
+    function will seed the pseudo-random number generator by calling qsrand().
 
     On a Windows platform, a GUID is generated, which almost certainly
     \e{will} be unique, on this or any other system, networked or not.
@@ -578,6 +580,8 @@ QT_BEGIN_INCLUDE_NAMESPACE
 #include "stdlib.h" // For srand/rand
 QT_END_INCLUDE_NAMESPACE
 
+extern void qsrand(); // in qglobal.cpp
+
 QUuid QUuid::createUuid()
 {
     static const int intbits = sizeof(int)*8;
@@ -585,10 +589,11 @@ QUuid QUuid::createUuid()
     if (!randbits) {
         int max = RAND_MAX;
         do { ++randbits; } while ((max=max>>1));
-        qsrand((uint)QDateTime::currentDateTime().toTime_t());
-        qrand(); // Skip first
     }
 
+    // reseed, but only if not already seeded
+    qsrand();
+
     QUuid result;
     uint *data = &(result.data1);
     int chunks = 16 / sizeof(uint);