New Post: Inside SQLCLR

You are sending either a null or an empty string to your Sql Pipe. Not sure whether this in intended, but just look at what R is doing even without R.NET with:

str(as.list(cat('Hello World!')))
str(as.list(s <- cat('Hello World!')))
str(s <- cat('Hello World!'))
as.character(s <- cat('Hello World!'))

If you call HelloWorldFromR several times, you should not call engine.Dispose more than once. As I recall, there should be an exception that state pretty clearly that the engine has been reinitialized/disposed more than once in the same process lifetime, something R cannot do.

Not enough information to figure out whether this explains why things "hang".