QSharedPointer: fix threadsafety docs

Try and explain better the situation around QSharedPointer:
it's reentrant, not thread safe.

Change-Id: Ief9d28be8ea3fbaa6014cb6b999626db1bab52ca
Reviewed-by: Martin Smith <martin.smith@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 13 insertions, 8 deletions

diff --git a/src/corelib/tools/qsharedpointer.cpp b/src/corelib/tools/qsharedpointer.cpp
index 95b584e914..b755941b73 100644
--- a/src/corelib/tools/qsharedpointer.cpp
+++ b/src/corelib/tools/qsharedpointer.cpp
@@ -65,14 +65,19 @@
 
     \section1 Thread-Safety
 
-    QSharedPointer and QWeakPointer are thread-safe and operate
-    atomically on the pointer value. Different threads can also access
-    the QSharedPointer or QWeakPointer pointing to the same object at
-    the same time without need for locking mechanisms.
-
-    It should be noted that, while the pointer value can be accessed
-    in this manner, QSharedPointer and QWeakPointer provide no
-    guarantee about the object being pointed to. Thread-safety and
+    QSharedPointer and QWeakPointer are reentrant classes. This means that, in
+    general, a given QSharedPointer or QWeakPointer object \b{cannot} be
+    accessed by multiple threads at the same time without synchronization.
+
+    Different QSharedPointer and QWeakPointer objects can safely be accessed
+    by multiple threads at the same time. This includes the case where they
+    hold pointers to the same object; the reference counting mechanism
+    is atomic, and no manual synchronization is required.
+
+    It should be noted that, while the pointer value can be accessed in this
+    manner (that is, by multiple threads at the same time, without
+    synchronization), QSharedPointer and QWeakPointer provide no guarantee
+    about the object being pointed to. The specific thread-safety and
     reentrancy rules for that object still apply.
 
     \section1 Other Pointer Classes