QObject: use per-thread storage for qFlagLocation()

qFlagLocation() uses a global char* array to transport source location
information from the connect() side to the metaobject side. The size
of the array is 2 (two), which just about suffices for a single connect()
statement.

Obviously, if more than one thread makes a (_any_) connection at the same
time, the data is useless and, worse, there's a data race.

The non-reentrancy of qFlagLocations() cannot and need not be fixed,
but use a per-thread flagged_locations array in QThreadData so threads
don't disturb each other.

Task-number: QTBUG-3680

Change-Id: If1797c60751f551694def69afee6fbe295bbe2d2
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/corelib/thread/qthread_p.h b/src/corelib/thread/qthread_p.h
index 5e4eedaac7..fa1f7414f1 100644
--- a/src/corelib/thread/qthread_p.h
+++ b/src/corelib/thread/qthread_p.h
@@ -242,6 +242,26 @@ public:
         return canWait;
     }
 
+    // This class provides per-thread (by way of being a QThreadData
+    // member) storage for qFlagLocation()
+    class FlaggedDebugSignatures
+    {
+        static const uint Count = 2;
+
+        uint idx;
+        const char* locations[Count];
+
+    public:
+        FlaggedDebugSignatures() : idx(0)
+        { std::fill_n(locations, Count, static_cast<char*>(0)); }
+
+        void store(const char* method)
+        { locations[idx++ % Count] = method; }
+
+        bool contains(const char *method) const
+        { return std::find(locations, locations + Count, method) != locations + Count; }
+    };
+
     QThread *thread;
     Qt::HANDLE threadId;
     bool quitNow;
@@ -252,6 +272,7 @@ public:
     bool canWait;
     QVector<void *> tls;
     bool isAdopted;
+    FlaggedDebugSignatures flaggedSignatures;
 };
 
 class QScopedLoopLevelCounter