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Message-ID: <43a42da1-433d-42fa-b018-b393177a5707@SystematicSW.ab.ca>
Date: Sun, 23 Mar 2025 17:06:38 -0600
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Subject: Re: Deadlock when calling pthread_key_create in the destructor of a
 pthread_key
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To: cygwin AT cygwin DOT com
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From: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
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Cc: Brian Inglis <Brian DOT Inglis AT SystematicSW DOT ab DOT ca>
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On 2025-03-23 06:32, Yuyi Wang via Cygwin wrote:
> It's a bug when I tried to run tests of Rust std lib. The standard
> library of Rust tries to create a new pthread_key in the destructor of a
> key created previously. Unfortunately, List::for_each locked the mutex
> before, so List_insert method cannot lock the mutex again.
> 
> I have searched though the POSIX docs and didn't find any words that one
> should not call pthread_key_create in the destructor of a pthread_key. I
> think it should be a bug of cygwin.

Destructor functions are intended to deallocate key storage at thread exit:

https://pubs.opengroup.org/onlinepubs/9799919799/functions/pthread_key_create.html
"RATIONALE
Destructor Functions
Normally, the value bound to a key on behalf of a particular thread is a pointer 
to storage allocated dynamically on behalf of the calling thread. The destructor 
functions specified with pthread_key_create() are intended to be used to free 
this storage when the thread exits."

although it later says:

"There is no notion of a destructor-safe function. If an application does not 
call pthread_exit() from a signal handler, or if it blocks any signal whose 
handler may call pthread_exit() while calling async-unsafe functions, all 
functions may be safely called from destructors."

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retrancher  but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

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