filesystem: Cache Directory instances

This is mostly aimed at keeping them alive so we can check for
modifications & external storage unmounting

src/factory/FileSystem.cpp

@@ -39,7 +39,13 @@ namespace factory
 
 std::shared_ptr<fs::IDirectory> FileSystemFactory::createDirectory( const std::string& path )
 {
-    return std::shared_ptr<fs::IDirectory>( new fs::Directory( path ) );
+    std::lock_guard<std::mutex> lock( m_mutex );
+    const auto it = m_dirs.find( path );
+    if ( it != end( m_dirs ) )
+        return it->second;
+    auto dir = std::make_shared<fs::Directory>( path );
+    m_dirs[path] = dir;
+    return dir;
 }
 
 std::unique_ptr<fs::IFile> FileSystemFactory::createFile(const std::string& fileName)

src/factory/FileSystem.h

@@ -24,6 +24,10 @@
 
 #include "factory/IFileSystem.h"
 
+#include <mutex>
+#include <string>
+#include <unordered_map>
+
 namespace factory
 {
     class FileSystemFactory : public IFileSystem
@@ -31,5 +35,9 @@ namespace factory
     public:
         virtual std::shared_ptr<fs::IDirectory> createDirectory( const std::string& path ) override;
         virtual std::unique_ptr<fs::IFile> createFile( const std::string& fileName ) override;
+
+    private:
+        std::unordered_map<std::string, std::shared_ptr<fs::IDirectory>> m_dirs;
+        std::mutex m_mutex;
     };
 }