src/juce_appframework/gui/components/windows/juce_ThreadWithProgressWindow.cpp

@@ -66,7 +66,10 @@ bool ThreadWithProgressWindow::runThread (const int priority)
     startThread (priority);
     startTimer (100);
 
-    alertWindow.setMessage (message);
+    {
+        const ScopedLock sl (messageLock);
+        alertWindow.setMessage (message);
+    }
 
     const bool wasCancelled = alertWindow.runModalLoop() != 0;
 
@@ -84,6 +87,7 @@ void ThreadWithProgressWindow::setProgress (const double newProgress)
 
 void ThreadWithProgressWindow::setStatusMessage (const String& newStatusMessage)
 {
+    const ScopedLock sl (messageLock);
     message = newStatusMessage;
 }
 
@@ -97,6 +101,7 @@ void ThreadWithProgressWindow::timerCallback()
     }
     else
     {
+        const ScopedLock sl (messageLock);
         alertWindow.setMessage (message);
     }
 }

src/juce_appframework/gui/components/windows/juce_ThreadWithProgressWindow.h

@@ -155,6 +155,7 @@ private:
     double progress;
     AlertWindow alertWindow;
     String message;
+    CriticalSection messageLock;
     const int timeOutMsWhenCancelling;
 
     ThreadWithProgressWindow (const ThreadWithProgressWindow&);