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Re: Concurrency via isolated process/thread


From: Po Lu
Subject: Re: Concurrency via isolated process/thread
Date: Fri, 07 Jul 2023 08:21:27 +0800
User-agent: Gnus/5.13 (Gnus v5.13)

Ihor Radchenko <yantar92@posteo.net> writes:

> Po Lu <luangruo@yahoo.com> writes:
>
>>>>>    LOCK_OBJECT (foo);
>>>>>    LOCK_OBJECT (XCAR (foo));
>>>> ...
>>> ...
>>> Do you mean that locking XCAR (foo) is unnecessary when foo is locked?
>>
>> No, that there is no need to lock a cons (or a vector, or anything else
>> with a fixed number of Lisp_Object slots) before reading or writing to
>> it.
>
> I feel confused here.
>
> My understanding is
>
>   CHECK_STRING (XCAR (foo));
>   <we do not want XCAR (foo) to be altered here>
>   foo = XSTRING (XCAR (foo));
>
> So, locking is needed to ensure that CHECK_STRING assertion remains valid.

No, what we want to make sure is that the same string whose type was
checked is extracted.  By not loading XCAR (foo) twice.


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