Revamped DomDocumentCache with regard to thread safety

* DomDocumentCache::item class now is _finalized_ by default and doesn't perform document instantiation, just lifetime management
** xercesc::DOMDocument is instantiated inside the external function implementations and committed to the document cache for conversion to a xalan document
* added mutex with scoped lock to prevent concurrent write access to the std::unordered_map contained withing DomDocumentCache
* functionality of the _get_ member method was split into _get_ and _create_
** added typedef for std::pair specialization type "optional_item" that functions as the return value of _create_ and _get_
* "locator->getSystemId()" was leaking memory as xerces doesn't manage the lifetime of the returned heap-allocated char array
** analog to XMLCh* strings
** transformed XercesStringGuard into template class to be instantiated on either XMLCh or char

1 files changed, 23 insertions, 5 deletions

diff --git a/src/support/xerces_string_guard.h b/src/support/xerces_string_guard.h
index f64a53e..7b9517a 100644
--- a/src/support/xerces_string_guard.h
+++ b/src/support/xerces_string_guard.h
@@ -7,15 +7,33 @@
 
 namespace InputXSLT {
 
+template <typename Type>
 class XercesStringGuard {
 	public:
-		XercesStringGuard(const std::string&);
-		~XercesStringGuard();
-
-		XMLCh* operator*();
+		XercesStringGuard(const Type* src):
+			string_(src) { }
+
+		XercesStringGuard(
+			const std::basic_string<
+				typename std::remove_pointer<decltype(
+					xercesc::XMLString::transcode(new Type[1])
+				)>::type
+			>& src
+		):
+			string_(xercesc::XMLString::transcode(src.data())) { }
+
+		~XercesStringGuard() {
+			xercesc::XMLString::release(
+				const_cast<Type**>(&this->string_)
+			);
+		}
+
+		inline const Type* operator*() const {
+			return this->string_;
+		}
 
 	private:
-		XMLCh* const string_;
+		const Type* const string_;
 
 };