various: added hooks so that various lengthy functions could be cancelled from another thread

app/common/CMakeLists.txt

@@ -18,6 +18,7 @@ set(OLIVE_SOURCES
   ${OLIVE_SOURCES}
   common/bezier.h
   common/bezier.cpp
+  common/cancelableobject.h
   common/channellayout.h
   common/clamp.h
   common/constructors.h

app/common/cancelableobject.h

@@ -0,0 +1,26 @@
+#ifndef CANCELABLEOBJECT_H
+#define CANCELABLEOBJECT_H
+
+#include <QAtomicInt>
+
+class CancelableObject {
+public:
+  CancelableObject() :
+    cancelled_(false)
+  {
+  }
+
+  void Cancel() {
+    cancelled_ = true;
+  }
+
+  const QAtomicInt& IsCancelled() const {
+    return cancelled_;
+  }
+
+private:
+  QAtomicInt cancelled_;
+
+};
+
+#endif // CANCELABLEOBJECT_H