From: Noam Postavsky <npostavs@gmail.com>
To: Hendrik Tews <hendrik@askra.de>
Cc: 13400@debbugs.gnu.org, Stefan Monnier <monnier@iro.umontreal.ca>
Subject: bug#13400: 23.4; overlapping process filter calls
Date: Fri, 26 Jul 2019 23:38:46 -0400 [thread overview]
Message-ID: <87o91guoxl.fsf@gmail.com> (raw)
In-Reply-To: <87r4ltpctd.fsf@wallace.tews.net> (Hendrik Tews's message of "Thu, 10 Jan 2013 11:11:42 +0100")
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Hendrik Tews <hendrik@askra.de> writes:
> because Stefan Monnier asked for it
> (http://lists.inf.ed.ac.uk/pipermail/proofgeneral-devel/2013/000296.html)
[Note: meanwhile the section number has changed to 38 instead of 37.]
> - Section "37.9 Receiving Output from Processes" does not list
> process-send-string. How about other blocking I/O functions?
In the attached patch, I've added a mention/xref for functions which send
data to processes.
> - Same in "37.9.2. Process Filter Functions"
This section is repeated twice (I addressed the second instance below).
> - Same in "37.4 Creating an Asynchronous Process" ,
> process-send-string is neither waiting for input not time
> delay.
I don't see any mention of process-send-string in that section, nor how
it's relevant to the rest of this report.
> - "37.7 Sending Input to Processes" says that filters can run
> inside process-send-string, but it could be clearer about the
> point that this can also happen inside the same filter for the
> same process.
I'm not really convinced that is necessary.
> - "37.9.2 Process Filter Functions" ignores the problem
> completely. There should be a paragraph clearly stating this
> problem. Further, it would be nice, if the filter function
> example could be extended to correctly deal with this problem.
I added a mention of the possibility of recursion. I'm not sure about
making an example (specifically, what is the best way to deal with this
problem?).
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From 022fb3f287d4fd351078f2b134d187ff584b380c Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Fri, 26 Jul 2019 23:20:37 -0400
Subject: [PATCH] Note that process filter can be called recursively
(Bug#13400)
* doc/lispref/processes.texi (Output from Processes): Note that
functions which send data may also trigger reading from processes.
(Filter Functions): Note that filter functions may be called
recursively.
---
doc/lispref/processes.texi | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi
index a93f4db428..208005772e 100644
--- a/doc/lispref/processes.texi
+++ b/doc/lispref/processes.texi
@@ -1416,9 +1416,10 @@ Output from Processes
Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input (see the function @code{waiting-for-user-input-p}),
-in @code{sit-for} and @code{sleep-for} (@pxref{Waiting}), and in
-@code{accept-process-output} (@pxref{Accepting Output}). This
-minimizes the problem of timing errors that usually plague parallel
+in @code{sit-for} and @code{sleep-for} (@pxref{Waiting}), in
+@code{accept-process-output} (@pxref{Accepting Output}), and in
+functions which send data to processes (pxref{Input to Processes}).
+This minimizes the problem of timing errors that usually plague parallel
programming. For example, you can safely create a process and only
then specify its buffer or filter function; no output can arrive
before you finish, if the code in between does not call any primitive
@@ -1683,6 +1684,10 @@ Filter Functions
or more batches of output; one way to do this is to insert the
received text into a temporary buffer, which can then be searched.
+Note that if the filter calls a function which can wait for process
+output (pxref{Output from Processes}), the filter may be called
+recursively.
+
@defun set-process-filter process filter
This function gives @var{process} the filter function @var{filter}. If
@var{filter} is @code{nil}, it gives the process the default filter,
--
2.11.0
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> To make it easier in the future to deal with this problem, I
> suggest to add a process specific flag
> ``process-no-concurrent-filters''. When this flag is t for a
> process, Emacs accepts output from this process inside a filter
> but buffers it without calling the filter. The call to the filter
> is delayed until a point where no filter for this process is
> running. An error is signaled, if the buffered output exceeds a
> certain size.
I thought of just making a wrapper in Lisp instead, this saves the need
to complicate the process C code with yet another flag; it's already
tricky enough as it is.
;;; -*- lexical-binding: t -*-
(defun make-buffered-filter (filter)
(let ((filtering nil)
(buffered nil)
(process nil))
(lambda (proc str)
(if process
(unless (eq process proc)
(error "Buffered filter used in different processes: %S, %S"
proc process))
(setq process proc))
(push str buffered)
(unless filtering
(setq filtering t)
(unwind-protect
(while buffered
(setq str (apply #'concat (nreverse buffered)))
(setq buffered nil)
(funcall filter proc str))
(setq filtering nil))))))
;; Can be used like
(set-process-filter my-process (make-buffered-filter #'my-filter-function))
next prev parent reply other threads:[~2019-07-27 3:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-10 10:11 bug#13400: 23.4; overlapping process filter calls Hendrik Tews
2019-07-27 3:38 ` Noam Postavsky [this message]
2019-07-27 8:24 ` Eli Zaretskii
2019-08-04 0:02 ` Noam Postavsky
2019-08-04 16:29 ` Eli Zaretskii
2019-08-05 18:31 ` Stefan Monnier
2019-08-08 3:37 ` Noam Postavsky
2019-08-08 13:36 ` Eli Zaretskii
2019-08-09 21:36 ` Stefan Monnier
2019-08-10 1:39 ` Noam Postavsky
2019-08-10 9:03 ` Stefan Monnier
2019-08-05 22:37 ` Hendrik Tews
2019-08-06 7:40 ` Stefan Monnier
2019-08-08 1:15 ` Noam Postavsky
2019-08-20 12:19 ` Noam Postavsky
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