From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Ihor Radchenko Newsgroups: gmane.emacs.devel Subject: Re: Emacs design and architecture. How about copy-on-write? 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:310814 Archived-At: Po Lu writes: >> If we have something like (let ((case-fold-search t)) ...), we will lock >> `case-fold-search' symbol for the whole duration of `let' call and block >> any other threads trying to alter `case-fold-search' locally. > > ... for > each thread must be capable of simultaneously binding different values > to the same variable. Sure. I did not object this. What I mean is that some symbol values are tricky. In particular symbols with values being forwarded. > In my implementation, struct thread_state incorporates pointers to all > forwarded variables, each of which either points within thread_state > itself when its symbol is bound locally, or to `globals' otherwise. > Vcharset_map_path thus becomes: > > #define Vcharset_map_path (*current_thread->f_Vcharset_map_path) Does it mean that each threads contains a copy of the whole `globals'? I think I proposed this in the linked thread and it was objected as something taking a lot of memory. IMHO, copy-of-write would be better here - only store the thread-local values that are actually altered by the thread. Indeed, a simple #define will not be enough then, but we would not waste memory copying the values that will never be changed anyway. > That being said, case-fold-search is a bad example. Which is why I used it :) It is innocent yet tricky. > ... I have not yet > established how buffer local variables will be efficiently represented > when multiple threads selecting the same buffer bind the same variables > simultaneously. We discussed asynchronous access to buffers earlier and concluded that modifying a buffer (and its buffer-local values) asynchronously is a hard problem. In particular, handling gap asynchronously is simply not possible. It might be more practical to allow simultaneous read-only access to the same buffer, but interlock writes to buffer object (including moving gap, changing buffer text, and changing buffer-local values). -- Ihor Radchenko // yantar92, Org mode contributor, Learn more about Org mode at . Support Org development at , or support my work at