StablePtr / StableName ?

[Simon Peyton Jones]

Add this conversation to #13165?

From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Simon Marlow
Sent: 24 January 2017 09:38
To: Johannes Waldmann <johannes.waldmann at htwk-leipzig.de>
Cc: ghc-devs at haskell.org
Subject: Re: StablePtr / StableName ?

StableNames do use the RTS hash table implementation, but StablePtr does *not*, the ticket is incorrect.  But to be clear, nothing has changed - StableName has always used this hash table implementation.  No doubt it could be faster if we used a better hash table, but whether it matters to you or not depends on what else your application is doing - is StableName in the inner loop? You'd have to measure it.

Cheers
Simon

On 22 January 2017 at 16:09, Johannes Waldmann <johannes.waldmann at htwk-leipzig.de<mailto:johannes.waldmann at htwk-leipzig.de>> wrote:
Dear ghc devs,

would the StablePtr performance issue (slow hash table)
https://ghc.haskell.org/trac/ghc/ticket/13165
also affect StableNames?
Cf. https://github.com/ekmett/ersatz/issues/30<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fekmett%2Fersatz%2Fissues%2F30&data=02%7C01%7Csimonpj%40microsoft.com%7Ca760f5ebb2ba4cc67f5408d4443cced5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636208475347266840&sdata=1%2Brv8d8bcOl1gCPFNe4alsfNPxpURZQiIjPgeR%2BBnrY%3D&reserved=0>

Could making 10^5 stable names, and accessing each just once,
take noticeable time? Where would this show up in a profile?

I guess there's no easy way to change the ersatz library
(StableName this is the fundamental mechanism for detecting sharing)
but if these issues are related, then ersatz provides a
performance test case.

Thanks, Johannes.
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