[ENH] DropIns - Prevention of File Locks and Unloading

[RenatoCapelo]

Enhancement Request

Context

At the present time there are two ways to insert drop-ins onto Elsa.

1. Via NuGet Packages

   • Unzips the package and loads each DLL onto memory
   • Doesn't lock the file since it's closed after copying the DLLs onto memory
   • When the original .npkg is deleted the associated drop-ins are not unregistered from the registry

2. Via DLLs

   • Loads directly the Assembly from the DLL
   • Locks the file since the Assembly is pointing to the DLL file

Planned Implementation

1. Change Drop-in Directory Monitor to allow tracking of the installed Drop-ins
   • Every time a drop-in is added, it should be added to a dictionary having the key as the path and the value the drop-ins associated to that file
2. Prevent the File locking of DLLs
   • Implement something similar to the NuGet's behavior (copy the DLL to a memory stream and load it from there). This will prevent the file locking.
     • If needed, this can possibly be improved on the future to copy the DLLs to an internal folder to not consume unbearable amounts of ram
3. Change Drop-ins to allow a safe unregister
   • Add a Unconfigure method to the IDropIn interface.
     • This method's implementation should unregister the activity from the registry as well as possible added services to the service provider.
4. Change Drop-ins Directory Monitor to keep track of deletion events
   • Add a callback function for the watcher.Deleted
     • This function will retrieve all drop-ins associated with the path that was deleted and call their Unconfigure method