Fix potential deadlock in QAbstractFileEngine

There's a possibility for deadlocking with user code in
QAbstractFileEngine. Changing the QMutex there to a QReadWriteLock
should reduce the possibilities for this happening.

Also reduced the scope of the lock in QAbstractFileEngine.

Reviewed-by: Thiago Macieira

1 files changed, 12 insertions, 10 deletions

diff --git a/src/corelib/io/qabstractfileengine.cpp b/src/corelib/io/qabstractfileengine.cpp
index 93097bc..9eb3305 100644
--- a/src/corelib/io/qabstractfileengine.cpp
+++ b/src/corelib/io/qabstractfileengine.cpp
@@ -42,7 +42,7 @@
 #include "qabstractfileengine.h"
 #include "private/qabstractfileengine_p.h"
 #include "qdatetime.h"
-#include "qmutex.h"
+#include "qreadwritelock.h"
 #include "qvariant.h"
 // built-in handlers
 #include "qfsfileengine.h"
@@ -98,14 +98,14 @@ QT_BEGIN_NAMESPACE
     All application-wide handlers are stored in this list. The mutex must be
     acquired to ensure thread safety.
  */
-Q_GLOBAL_STATIC_WITH_ARGS(QMutex, fileEngineHandlerMutex, (QMutex::Recursive))
+Q_GLOBAL_STATIC_WITH_ARGS(QReadWriteLock, fileEngineHandlerMutex, (QReadWriteLock::Recursive))
 static bool qt_abstractfileenginehandlerlist_shutDown = false;
 class QAbstractFileEngineHandlerList : public QList<QAbstractFileEngineHandler *>
 {
 public:
     ~QAbstractFileEngineHandlerList()
     {
-        QMutexLocker locker(fileEngineHandlerMutex());
+        QWriteLocker locker(fileEngineHandlerMutex());
         qt_abstractfileenginehandlerlist_shutDown = true;
     }
 };
@@ -122,7 +122,7 @@ Q_GLOBAL_STATIC(QAbstractFileEngineHandlerList, fileEngineHandlers)
  */
 QAbstractFileEngineHandler::QAbstractFileEngineHandler()
 {
-    QMutexLocker locker(fileEngineHandlerMutex());
+    QWriteLocker locker(fileEngineHandlerMutex());
     fileEngineHandlers()->prepend(this);
 }
 
@@ -132,7 +132,7 @@ QAbstractFileEngineHandler::QAbstractFileEngineHandler()
  */
 QAbstractFileEngineHandler::~QAbstractFileEngineHandler()
 {
-    QMutexLocker locker(fileEngineHandlerMutex());
+    QWriteLocker locker(fileEngineHandlerMutex());
     // Remove this handler from the handler list only if the list is valid.
     if (!qt_abstractfileenginehandlerlist_shutDown)
         fileEngineHandlers()->removeAll(this);
@@ -166,12 +166,14 @@ QAbstractFileEngineHandler::~QAbstractFileEngineHandler()
 */
 QAbstractFileEngine *QAbstractFileEngine::create(const QString &fileName)
 {
-    QMutexLocker locker(fileEngineHandlerMutex());
+    {
+        QReadLocker locker(fileEngineHandlerMutex());
 
-    // check for registered handlers that can load the file
-    for (int i = 0; i < fileEngineHandlers()->size(); i++) {
-        if (QAbstractFileEngine *ret = fileEngineHandlers()->at(i)->create(fileName))
-            return ret;
+        // check for registered handlers that can load the file
+        for (int i = 0; i < fileEngineHandlers()->size(); i++) {
+            if (QAbstractFileEngine *ret = fileEngineHandlers()->at(i)->create(fileName))
+                return ret;
+        }
     }
 
 #ifdef QT_BUILD_CORE_LIB