bug close-db twice.

[jin-park-dev]

I discovered strange behaviour with 'close-db'. I'm using latest version '0.8.1-13'
I'm on WSL2 and VSCode with Calva.

1. After running (duckdb/close-db), I can still do things with conn. Seems unintuitive but maybe this is intended behaviour?
2. I run (duckdb/close-db db) again, my nREPL disconnects.

I attached example code below with tutorial from readme and doing close-db twice.

;; Standard tutorial from README

(duckdb/initialize!)

(def stocks
  (-> (ds/->dataset "https://github.com/techascent/tech.ml.dataset/raw/master/test/data/stocks.csv" {:key-fn keyword})
      (vary-meta assoc :name :stocks)))

(def db (duckdb/open-db))
(def conn (duckdb/connect db))
(duckdb/create-table! conn stocks)
(duckdb/insert-dataset! conn stocks)

(ds/head (duckdb/sql->dataset conn "select * from stocks"))


;; buggy part
(duckdb/close-db db)
(ds/head (duckdb/sql->dataset conn "select * from stocks"))  ; after closing-db this still works?

(duckdb/close-db db) ; nREPL Connection was closed. Why my nREPL getting disconnected?

Many thanks for TMD <3

[jin-park-dev]

Small update.
Above is on duckdb v0.8.1 with bashscript example (from readme)
Tried on duckdb v0.9.2 and same nREPL disconnect.

[cnuernber]

The REPL is disconnected because the process crashes - double free in C is often a crash-level bug leading immediately to segfaults.

The connection still works because it has a shared pointer to the database - you need to close both the database and the connection to terminate the duckdb instance under the covers.

I am not certain this points to any real issue. What solutions do you expect from this?

[jin-park-dev]

Connection part makes sense thanks for explaining.

Running close-db twice and getting disconnect from REPL still seem like unexpected behaviour.
If reason is C code crashing causing REPL to disconnect, it seems to me there can be some kind of check not reach that state.

If you think otherwise, feel free to close.

[cnuernber]

I think it isn't fixable at the lowest level as dt-ffi pointers are immutable - but I think perhaps the opendb and open-connection pathways could return java.lang.AutoCloseable objects that could themselves have mutable ptr fields and would - as is common throughout java - quietly ignore or perhaps just warn on double close.

Are you interested doing this work in a PR?

[jin-park-dev]

I'm currently away for next 2 days. When I'm back I'll have a look at it.

[cnuernber]

Sounds great - here are a quick time savers for when you get back. There is a protocol used to get the actual pointer from the object passed in - this allows a generic deftype to behave like a pointer and then you can overload various things such as adding closeable and potentially overriding toString.