Fix race condition in QDateTime::timeZone() and other methods

When timezone support for QDateTime was added, we decided it was a good
idea to delay creating the QTimeZone object and checking that the time
is valid in that timezone (including for local time) until the user
requested that information. Unfortunately, QExplicitlySharedDataPointer
returns a non-const T* in operator->(), which meant we were accidentally
modifying the d pointer's contents in const methods, which in turn means
those const methods were not thread-safe when operating on the same
object.

This commit changes the d pointer to QSharedDataPointer, which is safer
in this regard and pointed out where the issues with constness were
located. Since we can't lazily calculate QTimeZone anymore, we need to
do it whenever the date, time or offset changes.

Task-number: QTBUG-43703
Change-Id: Ic5d393bfd36e48a193fcffff13b9686ef4ef1454
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 5 insertions, 9 deletions

diff --git a/src/corelib/tools/qdatetime_p.h b/src/corelib/tools/qdatetime_p.h
index a139390a9d..b8934f7f70 100644
--- a/src/corelib/tools/qdatetime_p.h
+++ b/src/corelib/tools/qdatetime_p.h
@@ -79,10 +79,9 @@ public:
     enum StatusFlag {
         NullDate            = 0x01,
         NullTime            = 0x02,
-        ValidDate           = 0x04,
-        ValidTime           = 0x08,
-        ValidDateTime       = 0x10,
-        TimeZoneCached      = 0x20,
+        ValidDate           = 0x04, // just the date field
+        ValidTime           = 0x08, // just the time field
+        ValidDateTime       = 0x10, // the whole object (including timezone)
         SetToStandardTime   = 0x40,
         SetToDaylightTime   = 0x80
     };
@@ -120,7 +119,7 @@ public:
     DaylightStatus daylightStatus() const;
 
     // Returns msecs since epoch, assumes offset value is current
-    inline qint64 toMSecsSinceEpoch() const { return (m_msecs - (m_offsetFromUtc * 1000)); }
+    inline qint64 toMSecsSinceEpoch() const;
 
     void checkValidDateTime();
     void refreshDateTime();
@@ -133,14 +132,11 @@ public:
     inline bool isValidDateTime() const { return m_status & ValidDateTime; }
     inline void setValidDateTime() { m_status |= ValidDateTime; }
     inline void clearValidDateTime() { m_status &= ~ValidDateTime; }
-    inline bool isTimeZoneCached() const { return m_status & TimeZoneCached; }
-    inline void setTimeZoneCached() { m_status |= TimeZoneCached; }
-    inline void clearTimeZoneCached() { m_status &= ~TimeZoneCached; }
     inline void clearSetToDaylightStatus() { m_status &= ~(SetToStandardTime | SetToDaylightTime); }
 
 #ifndef QT_BOOTSTRAPPED
     static qint64 zoneMSecsToEpochMSecs(qint64 msecs, const QTimeZone &zone,
-                                        QDate *localDate, QTime *localTime);
+                                        QDate *localDate = 0, QTime *localTime = 0);
 #endif // QT_BOOTSTRAPPED
 
     static inline qint64 minJd() { return QDate::minJd(); }