# Futures in 8.4 cs and 8.4 bc **URL:** \ **Category:** Questions & Answers\ **Tags:** question\ **Created:** [March 19, 2022, 4:55pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809 "2022-03-19T16:55:41Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![joskoot](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/joskoot/32/1964_2.png) [@joskoot](https://racket.discourse.group/u/joskoot)\ **Post date:** [March 19, 2022, 4:55pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/1 "2022-03-19T16:55:42Z")
Hi I have a program using futures. It runs very well with DrRacket 8.4 cs. With DrRacket 8.4 bc it seems to use one processor only. Is this a known problem? If not I can send the source code (about 500 lines) Details: debugging off, Windows 10. Best wishes, Jos Koot ---
**Author:** ![ryanc](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/ryanc/32/71_2.png) [@ryanc](https://racket.discourse.group/u/ryanc)\ **Post date:** [March 19, 2022, 5:39pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/2 "2022-03-19T17:39:28Z")
One of the advantages of Racket CS is that more operations are future-safe. See the discussion in [racket/racket/src/thread/README.txt](https://github.com/racket/racket/blob/master/racket/src/thread/README.txt) for more information. ---
**Author:** ![joskoot](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/joskoot/32/1964_2.png) [@joskoot](https://racket.discourse.group/u/joskoot)\ **Post date:** [March 19, 2022, 6:45pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/3 "2022-03-19T18:45:34Z")
Thanks Ryan, That may explain things, although I don't see any unsafe operations in my code (proper lists and exact integers only) (no mutable objects, no hashes, no mpairs, no vectors, no boxes, no semaphores, no etc) Jos ---
**Author:** ![ryanc](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/ryanc/32/71_2.png) [@ryanc](https://racket.discourse.group/u/ryanc)\ **Post date:** [March 19, 2022, 8:09pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/4 "2022-03-19T20:09:26Z")
Have you tried using the [futures visualizer](https://docs.racket-lang.org/future-visualizer/index.html) to see what operations your futures are blocking on? ---
**Author:** ![joskoot](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/joskoot/32/1964_2.png) [@joskoot](https://racket.discourse.group/u/joskoot)\ **Post date:** [March 19, 2022, 8:41pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/5 "2022-03-19T20:41:28Z")
I’ll try that, Jos ![DC369554041A4649A528B20B10730B39.png](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/2ad4c25f471d2cfc2782215e9bb5a535b2545175.png) ---
**Author:** ![joskoot](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/joskoot/32/1964_2.png) [@joskoot](https://racket.discourse.group/u/joskoot)\ **Post date:** [March 19, 2022, 9:04pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/6 "2022-03-19T21:04:54Z")
BC: ![9842F364F723414C916F2E049DB5D6CD.png](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/8887d057cefdd70bdc8a8535deaf613eca294e5c.png) CS ![C0D8CA652B0C4BA188EEE279BF48D6AE.png](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/a05ed84c4012c914ed3b2c8f6d2c2622efcf79ee.png) Is it the garbage collector that is blocking? Thanks, Jos ![DC369554041A4649A528B20B10730B39.png](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/2ad4c25f471d2cfc2782215e9bb5a535b2545175.png) ---
**Author:** ![ryanc](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/ryanc/32/71_2.png) [@ryanc](https://racket.discourse.group/u/ryanc)\ **Post date:** [March 20, 2022, 10:41am UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/7 "2022-03-20T10:41:24Z")
It means it's blocking on the `+` operation. IIUC, in Racket BC `+` is only future-safe if it is inlined by the JIT and if only the fast (fixnum-only) path is executed. In my experiments, using `+` in a higher-order way caused the future to block; for example: `(foldl + 0 xs)`. When I rewrote that to `(foldl (lambda (a b) (+ a b)) 0 xs)` then the future did not block. I had hoped that the compiler would inline `foldl` and put `+` in a direct-call position so the JIT can inline it, but it didn't. (Tested on Racket BC 8.1.) ---
**Author:** ![joskoot](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/joskoot/32/1964_2.png) [@joskoot](https://racket.discourse.group/u/joskoot)\ **Post date:** [March 20, 2022, 2:52pm UTC](https://racket.discourse.group/t/futures-in-8-4-cs-and-8-4-bc/809/8 "2022-03-20T14:52:48Z")
Hi Ryan, Thanks for your clear explanation. I tried some modifications to enhance inlining, but without luck. I’ll use CS. Thanks again, Jos ![A05275C433EC4658AD04B6A7586C7F72.png](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/8ee32840a19a65d452c6afb8dc2804ae7ae28c70.png)