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Re: Access violation in Curl_hash_add

From: Daniel Stenberg <>
Date: Fri, 9 Dec 2016 00:43:54 +0100 (CET)

On Thu, 8 Dec 2016, Jake Fehr (jfehr) wrote:

> We are getting crash reports in the field that are pointing to
> Curl_hash_add.

We have a bunch of unit tests for the hash functions and they have been
working like this for many years. I'm not ruling out that there can still be
bugs in there, but I am suggesting that it is more likely something else that
causes these crashes.

We've seen similar crash reports in the past when libcurl has been used multi-
threaded but without the necessary precautions to avoid parallel use of the
same handles. Any chance that could be happening here as well?

> We noticed the same crash in 7.50.1 and 7.51. Ióm not sure when this may
> have been introduced. We jumped from 7.3x to 7.50.1 so it may exist in 7.4x
> variants as well.

The hash code has not changed in any notable way since 7.30.0 so if there's a
hash problem now, it probably existed in 7.3x.x too...

> Any thoughts on what might be causing this?

Your stack trace shows these hashes being used from conncache.c so maybe
that's to blame if multi-threading issues can be ruled out.

Any chance you can bisect when the problem occured? Or try to provide us with
an example code that reproduces this?


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Received on 2016-12-09