logic: improved performance of initializing the fulltext search index

* implemented using multithreaing for building the fulltext search index
* also: decreased ideal thread count by 1 to keep the machine responsive while indexing and building the index

src/lib/utility/utility.h

@@ -28,6 +28,9 @@ namespace utility
 	std::string timeToString(const boost::posix_time::ptime time);
 	std::string timeToString(float seconds);
 
+	template<typename T>
+	std::vector<std::vector<T>> splitToEqualySizedParts(const std::vector<T>& values, const size_t desiredPartCount);
+
 	template<typename T>
 	std::vector<T> concat(const std::vector<T>& a, const std::vector<T>& b);
 
@@ -128,6 +131,27 @@ namespace utility
 	int roundToInt(float n);
 }
 
+template<typename T>
+std::vector<std::vector<T>> utility::splitToEqualySizedParts(const std::vector<T>& values, const size_t desiredPartCount)
+{
+	const size_t partCount = std::max<size_t>(1, std::min(desiredPartCount, values.size()));
+
+	std::vector<std::vector<T>> parts;
+	for (size_t i = 0; i < partCount; i++)
+	{
+		parts.push_back(std::vector<T>());
+	}
+
+	int i = 0;
+	for (const T& value : values)
+	{
+		parts[i % partCount].push_back(value);
+		++i;
+	}
+
+	return parts;
+}
+
 template<typename T>
 std::vector<T> utility::concat(const std::vector<T>& a, const std::vector<T>& b)
 {