Add copy variant of SharedPV::fetch()

src/sharedpv.cpp

@@ -407,7 +407,7 @@ void SharedPV::post(const Value& val)
     }
 }
 
-void SharedPV::fetch(Value& val)
+void SharedPV::fetch(Value& val) const
 {
     if(!impl)
         throw std::logic_error("Empty SharedPV");
@@ -421,6 +421,20 @@ void SharedPV::fetch(Value& val)
     }
 }
 
+Value SharedPV::fetch() const
+{
+    if(!impl)
+        throw std::logic_error("Empty SharedPV");
+
+    Guard G(impl->lock);
+
+    if(impl->current) {
+        return impl->current.clone();
+    } else {
+        throw std::logic_error("open() first");
+    }
+}
+
 struct StaticSource::Impl : public Source
 {
     RWLock lock;