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, 8 insertions, 2 deletions

diff --git a/src/support/dom/document_cache.h b/src/support/dom/document_cache.h
index 287a316..af99102 100644
--- a/src/support/dom/document_cache.h
+++ b/src/support/dom/document_cache.h
@@ -1,8 +1,11 @@
 #ifndef INPUTXSLT_SRC_SUPPORT_DOM_DOCUMENT_CACHE_H_
 #define INPUTXSLT_SRC_SUPPORT_DOM_DOCUMENT_CACHE_H_
 
-#include <unordered_map>
+#include <xercesc/dom/DOMDocument.hpp>
+
 #include <string>
+#include <mutex>
+#include <unordered_map>
 #include <memory>
 
 namespace InputXSLT {
@@ -10,12 +13,15 @@ namespace InputXSLT {
 class DomDocumentCache {
 	public:
 		class item;
+		typedef std::pair<bool, item*> optional_item;
 
 		DomDocumentCache();
 
-		item* get(const std::string&);
+		optional_item get(const std::string&);
+		optional_item create(const std::string&, xercesc::DOMDocument*);
 
 	private:
+		std::mutex write_mutex_;
 		std::unordered_map<std::string, std::unique_ptr<item>> map_;
 
 };