From: Tom Tromey <tromey@redhat.com>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: Emacs development discussions <emacs-devel@gnu.org>
Subject: Re: advice needed for multi-threading patch
Date: Tue, 22 Sep 2009 21:16:07 -0600 [thread overview]
Message-ID: <m31vlyqrk8.fsf@fleche.redhat.com> (raw)
In-Reply-To: <jwvab0nqdag.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Tue, 22 Sep 2009 10:24:15 -0400")
Tom> This works great as long as the C code follows lispy rules. However, I
Tom> don't think that is always the case -- there are places doing direct
Tom> assignment to some of these variables where, really, a per-thread
Tom> assignment is meant.
Stefan> I'm not sure what you mean. Are you still talking about objfwd
Stefan> variables?
Yeah. What I meant here is that specbind has a little extra code in it
to install a Lisp_ThreadLocal object when needed. So, if the C code
uses specbind to do let-like binding, everything will work fine. If the
C code does not do this, then things will break.
For example, I am not certain that Vquit_flag is handled in a "safe"
way. It is directly assigned to in a number of places, but those
assignments should probably be thread-local. (This isn't the greatest
example, maybe, because Vquit_flag is also bound up in keyboard locking
and maybe other issues.)
Tom> Right now when a thread yields it does not release its buffer lock.
Stefan> I think it should, unless some of the buffer-local variables are
Stefan> let-bound by the thread.
I've been thinking about this a bit. It is trickier than it seems,
because a thread can actually have let-bindings for buffer-locals from
multiple buffers at the same time. There's an example of this in the
elisp manual. (This is also an area the threading code does not handle
well yet.)
I think this means it does not suffice to keep a simple per-thread count
of buffer-local bindings.
While thinking about this I realized that (I think) the current code
does the wrong thing if one thread let-binds a variable and then another
thread calls make-variable-buffer-local on it.
Stefan> Maybe another way to look at all these problems is to take an
Stefan> "agent" point of view: rather than threads moving around, we
Stefan> could consider each keyboard and each buffer as an active object
Stefan> (i.e. with its own thread), which communicate among each other.
Stefan> I.e. a buffer-thread never leaves its buffer, instead it does an
Stefan> RPC to another buffer-thread, or to a keyboard-thread, ...
I had considered the agent model -- that, plus a discussion on irc, is
actually what lead me to ask about running a second Emacs as a
subprocess.
It is hard for me to see how this could be done in a compatible way.
Right now elisp operates with few constraints; an elisp program can call
select-frame, which seems to imply that per-frame or per-keyboard
threads can't be done.
Tom> Yeah. I just wonder why nobody has done it and whether it would not be
Tom> a better approach.
Stefan> IIUC people do it all the time, tho not with another Emacs
Stefan> process: with an hexl process, a shell process, an openssl
Stefan> process, ... Emacs currently is not very good at using
Stefan> stdin/stdout so running an inferior Emacs process is poorly
Stefan> supported.
If I were doing it "for real" I might consider coming up with a
higher-bandwidth way to transfer an entire buffer between processes.
But, a princ/read approach could be done without modifying Emacs, by
having the parent Emacs make a server socket, and then passing the port
number to the subprocess as an argument. This avoids the stdin/stdout
difficulties.
One thing that would help me is having a concrete idea of what subset of
features would make this work be actually useful. I mostly implemented
it because it was cool, and because Giuseppe's initial patch convinced
me that it was possible (before that I'd written it off as totally
impractical). Now that a proof of concept works it would be nice to
have a concrete goal.
Tom
next prev parent reply other threads:[~2009-09-23 3:16 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-26 4:38 advice needed for multi-threading patch Tom Tromey
2009-08-26 7:06 ` Ken Raeburn
2009-08-26 14:52 ` Stefan Monnier
2009-08-26 18:50 ` Ken Raeburn
2009-08-27 3:12 ` Stefan Monnier
2009-08-27 6:28 ` Ken Raeburn
2009-08-27 17:02 ` Stefan Monnier
2009-08-26 16:08 ` Tom Tromey
2009-08-26 18:50 ` Ken Raeburn
2009-08-27 5:07 ` Miles Bader
2009-08-27 6:39 ` Ken Raeburn
2009-08-27 6:50 ` Miles Bader
2009-08-28 20:48 ` Juri Linkov
2009-08-28 22:15 ` Miles Bader
2009-08-28 23:27 ` Juri Linkov
2009-08-28 23:54 ` Miles Bader
2009-08-29 20:21 ` Richard Stallman
2009-08-26 15:02 ` Stefan Monnier
2009-08-26 15:31 ` Tom Tromey
2009-08-26 19:18 ` Stefan Monnier
2009-09-18 22:59 ` Tom Tromey
2009-09-19 0:09 ` Stephen J. Turnbull
2009-09-19 0:32 ` Chong Yidong
2009-09-21 21:19 ` Stefan Monnier
2009-09-21 21:50 ` Tom Tromey
2009-09-22 14:24 ` Stefan Monnier
2009-09-22 23:59 ` Ken Raeburn
2009-09-23 3:11 ` Stefan Monnier
2009-09-23 15:53 ` Chong Yidong
2009-09-23 3:16 ` Tom Tromey [this message]
2009-09-24 17:25 ` Stefan Monnier
2009-09-24 17:57 ` Tom Tromey
2009-09-27 20:59 ` Tom Tromey
2009-09-27 23:05 ` Stefan Monnier
2009-09-28 4:27 ` Tom Tromey
2009-09-29 0:27 ` Stefan Monnier
2009-09-29 2:26 ` Ken Raeburn
2009-09-29 3:20 ` Stefan Monnier
2009-09-29 3:57 ` Ken Raeburn
2009-09-29 3:33 ` Tom Tromey
2009-09-29 4:07 ` Ken Raeburn
2009-09-29 2:30 ` Tom Tromey
2009-09-23 18:43 ` Giuseppe Scrivano
2009-09-24 17:29 ` Stefan Monnier
2009-09-24 18:53 ` Giuseppe Scrivano
2009-09-24 20:04 ` Tom Tromey
2009-09-24 21:59 ` Stefan Monnier
2009-09-24 22:23 ` Giuseppe Scrivano
2009-09-24 22:47 ` Ken Raeburn
2009-09-28 14:52 ` Ted Zlatanov
2009-10-05 6:02 ` joakim
2009-09-28 7:44 ` Lynbech Christian
2009-08-29 0:28 ` Giuseppe Scrivano
2009-08-29 4:57 ` Tom Tromey
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