# How can I properly thread serve/servlet? **URL:** \ **Category:** Questions & Answers\ **Tags:** repl, web-server, thread\ **Created:** [November 15, 2024, 3:56pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326 "2024-11-15T15:56:02Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![mfru](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/mfru/32/2040_2.png) [@mfru](https://racket.discourse.group/u/mfru)\ **Post date:** [November 15, 2024, 3:56pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326/1 "2024-11-15T15:56:02Z")
Hi, I am working on a Racket web server. Having used Clojure in the past, I quite like being able to have convenience procedures for working within my code. Particularly, I want to implement a `(start-server!)` and a `(stop-server!)` procedure that enable me to start / stop the web-server within the current REPL. My approach so far looks like this: ```scheme #lang/racket ;; (...) (define servlet-thread #f) (define (start-server!) (unless servlet-thread (set! servlet-thread (thread (thunk (serve/servlet app-dispatch #:launch-browser? #f #:port 8080 #:server-root-path (build-path (current-directory)) #:servlet-path "/" #:listen-ip #f #:log-file (build-path "app.log") #:extra-files-paths (list "htdocs"))))))) (define (stop-server!) (kill-thread servlet-thread) ;; (set! servlet-thread #f) ) ``` Starting the server works fine and I can continue using the REPL, but when running `(stop-server!)` nothing really happens. The thread is dead according to `(thread-dead?)`, but I can still reach and interact with my server when browsing to `localhost:8080`. Why is that? I expected the thread to be actually dead and not executing code anymore. ---
**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\ **Post date:** [November 15, 2024, 4:51pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326/2 "2024-11-15T16:51:01Z")
Check me on this: when you run `serve/servlet` without the thread wrapper, it returns immediately after starting the server, right? Assuming so: the thread you started will die as soon as the call to `serve/servlet` returns. You can probably also check this by calling `thread-dead?` _before_ you call `stop-server!`. I believe you will find that the thread dies immediately when the server starts up. In order to get the behavior you want, I suspect you will either need to - find a function in the web-server interface that lets you inspect and halt running server instances, or - start the server with a lower-level blocking call that does not immediately return, but actually runs the (main?) web server thread on the current thread. There are other heavier-handed approaches, e.g. custodians or literally running another process using `process` or `system` or similar. ... But I bet there's a way to do this using only web server functions. John ---
**Author:** ![mfru](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/mfru/32/2040_2.png) [@mfru](https://racket.discourse.group/u/mfru)\ **Post date:** [November 15, 2024, 5:02pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326/3 "2024-11-15T17:02:37Z")
When I run `start-server!` and then check `(thread-dead? servlet-thread)` I get `#f`. Furthermore, when just running `serve/servlet` the procedure blocks and the server is listening to incoming requests: ```plaintext Your Web application is running at http://localhost:8080. Stop this program at any time to terminate the Web Server. ``` Indeed I then cannot run further procedures in the same REPL (unlike with `start-server!`) until I CTRL-C. I'll try to have a look if I can find other functions in the web-server interface that might suit my needs more, thanks. ---
**Author:** ![bogdan](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/bogdan/32/8_2.png) [@bogdan](https://racket.discourse.group/u/bogdan)\ **Post date:** [November 15, 2024, 5:06pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326/4 "2024-11-15T17:06:56Z")
You want one of the procedures listed here: [3 Launching Servers](https://docs.racket-lang.org/web-server-internal/web-server.html) . My preference is to always use `serve`, which returns a procedure that can be used to stop the server. [This post](https://defn.io/2020/02/12/racket-web-server-guide/) might also be helpful. Also, generally, `kill-thread` should be avoided unless you know (i.e. the documentation mentions) that the data structures used by the thread you're killing are kill-safe. ---
**Author:** ![mfru](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/mfru/32/2040_2.png) [@mfru](https://racket.discourse.group/u/mfru)\ **Post date:** [November 15, 2024, 5:41pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326/5 "2024-11-15T17:41:27Z")
This seems to be the way to go, experimenting right now with `serve`. I will post my working result and resolve the thread when finished, thank you. ---
**Author:** ![mfru](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/mfru/32/2040_2.png) [@mfru](https://racket.discourse.group/u/mfru)\ **Post date:** [November 16, 2024, 10:27pm UTC](https://racket.discourse.group/t/how-can-i-properly-thread-serve-servlet/3326/6 "2024-11-16T22:27:41Z")
I ended up with the following: ```scheme ;; (...) (define servlet-thread #f) (define server-semaphore (make-semaphore 0)) (define (start-server!) (unless servlet-thread (set! servlet-thread (thread (thunk (let ([stop (serve #:dispatch (sequencer:make (dispatch/servlet app) (dispatch/servlet not-found)) #:listen-ip "127.0.0.1" #:port 8080)]) (semaphore-wait server-semaphore) (stop))))))) (define (stop-server!) (unless (thread-dead? servlet-thread) (semaphore-post server-semaphore))) ``` Works for me 🙂