[racket] How to clean up a database connection in a program running in DrRacket?

Which version of Racket are you using? I think Ryan pushed some custodian
related improvements to the db library recently.

Robby

On Friday, December 26, 2014, Dmitry Pavlov <dpavlov at ipa.nw.ru> wrote:

> Hello,
>
> Let us say I put this program into DrRacket's Definitions window:
>
> -----------------------------------------------------------------
> #lang racket
> (require db)
>
> (define path "aaa.db")
>
> (when (file-exists? path)
>   (delete-directory/files path))
>
> (define conn (sqlite3-connect #:database path #:mode 'create))
> -----------------------------------------------------------------
>
> and then press the "Run" button. After that, I play with conn
> in the Interactions window. When I have played enough,
> I press the "Run" button again. Here is what I get:
>
> delete-file: cannot delete file
>   path: [...]\aaa.db
>   system error: Permission denied; errno=13
>
> The reason is that I forgot to (disconnect conn) in the end.
> (I get that only on Windows; Linux is OK with removing opened files).
>
> How do I disconnect automatically? Putting the (disconnect conn)
> into the Definitions window is not a solution, as I want to use
> conn in the Interactions (also I want to be safe against the
> "Stop" button pressed in the middle of the program before the
> disconnect happens)
>
> I tried to use a will executor:
>
> -----------------------------------------------------------------
> (define an-executor (make-will-executor))
> (void
>    (thread
>     (lambda ()
>       (let loop ()
>         (will-execute an-executor)
>         (loop)))))
>
> (define (executor-proc v) (printf "I am now garbage\n") (disconnect v))
> (will-register an-executor conn executor-proc)
> -----------------------------------------------------------------
>
> Surprisingly, it did not work for the database connection (while it
> does work for other kinds of objects), and I have no idea why. It
> does not work even with I call the GC explicitly:
>
> -----------------------------------------------------------------
> (set! conn #f)
> (collect-garbage)
> -----------------------------------------------------------------
>
> Is it possible to make the will executor work?
> Generally speaking, what is the recommended way to do this kind
> of thing?
>
>
> Best regards,
>
> Dmitry
>
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>
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