Re: Emacs design and architecture. How about copy-on-write?

[Emanuel Berg]

Eli Zaretskii wrote:

>>> If we need to lock 99.99% of Emacs "single" variables, it
>>> is easier to lock everything. Faster, too.
>> 
>> Why do we need to do that?
>> 
>> For one thread, one write operation, and one variable, only
>> that variable has to be locked?
>> 
>> (operate-on var1) ; here we need a lock on var1
>> (operate-on var2) ; etc
>
> We don't have 'operate' in Emacs, but we do have setq, setf,
> and others. Where do you locak and where do you unlock in
> that case?
>
> Just try to write a simplest Lisp program, and you will see
> the problem.

There is no way around it, in order to prevent a race
condition any global variable must be locked before it's value
can be altered.

So `setq', `setf' and any other setter of global variables
must first be refered to the locking mechanism where they
either acquire the lock, perform the write, and release the
lock; or, if the variable is already locked by some other
thread wanting to do the same thing, they must be queued so
they will get it in due time.

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