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, 21 insertions, 11 deletions

diff --git a/src/support/dom/document_cache.cc b/src/support/dom/document_cache.cc
index 1573af8..c4c57d3 100644
--- a/src/support/dom/document_cache.cc
+++ b/src/support/dom/document_cache.cc
@@ -5,23 +5,33 @@
 namespace InputXSLT {
 
 DomDocumentCache::DomDocumentCache():
+	write_mutex_(),
 	map_() { }
 
-DomDocumentCache::item* DomDocumentCache::get(const std::string& key) {
+DomDocumentCache::optional_item DomDocumentCache::get(const std::string& key) {
 	auto itemIter = this->map_.find(key);
 
 	if ( itemIter == this->map_.end() ) {
-		auto result = this->map_.emplace(
-			std::make_pair(key, std::unique_ptr<item>(new item("content")))
-		);
-
-		if ( result.second ) {
-			return (*(result.first)).second.get();
-		} else {
-			throw std::out_of_range("failed to instantiate DomDocumentCache");
-		}
+		return optional_item(false, nullptr);
 	} else {
-		return (*itemIter).second.get();
+		return optional_item(true, (*itemIter).second.get());
+	}
+}
+
+DomDocumentCache::optional_item DomDocumentCache::create(
+	const std::string&    key,
+	xercesc::DOMDocument* document
+) {
+	std::lock_guard<std::mutex> guard(this->write_mutex_);
+
+	auto result = this->map_.emplace(
+		std::make_pair(key, std::unique_ptr<item>(new item(document)))
+	);
+
+	if ( result.second ) {
+		return optional_item(true, (*(result.first)).second.get());
+	} else {
+		return optional_item(false, nullptr);
 	}
 }