QtConcurrent::ReduceKernel: fix race conditions

resultsMapSize is modified inside the runReduce() method, and the
writes are protected via mutex lock. However, reads of resultsMapSize
through shouldThrottle()/shouldStartThread() (that can be called by
multiple threads) are done without a lock. Added the missing locks.

Task-number: QTBUG-104787
Pick-to: 6.4 6.3 6.2 5.15
Change-Id: I700e7b66e67025bc7f570bc8ad69409b82675049
Reviewed-by: Jarek Kobus <[email protected]>
Reviewed-by: Marc Mutz <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/concurrent/qtconcurrentreducekernel.h b/src/concurrent/qtconcurrentreducekernel.h
index a58739fc410..a2c693d9e2e 100644
--- a/src/concurrent/qtconcurrentreducekernel.h
+++ b/src/concurrent/qtconcurrentreducekernel.h
@@ -187,11 +187,13 @@ public:
 
     inline bool shouldThrottle()
     {
+        std::lock_guard<QMutex> locker(mutex);
         return (resultsMapSize > (ReduceQueueThrottleLimit * threadCount));
     }
 
     inline bool shouldStartThread()
     {
+        std::lock_guard<QMutex> locker(mutex);
         return (resultsMapSize <= (ReduceQueueStartLimit * threadCount));
     }
 };