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bug#48118: 27.1; 28; Only first process receives output with multiple ru
From: |
miha |
Subject: |
bug#48118: 27.1; 28; Only first process receives output with multiple running processes |
Date: |
Tue, 25 May 2021 17:18:22 +0200 |
Eli Zaretskii <eliz@gnu.org> writes:
>> From: miha@kamnitnik.top
>> Cc: mail@daniel-mendler.de, eliz@gnu.org, 48118@debbugs.gnu.org
>> Date: Mon, 24 May 2021 23:05:47 +0200
>>
>> I propose the following simple patch. It makes output from multiple
>> /bin/yes programs arrive at the same rate and multiple grep processes
>> can run without them seemingly blocking each other.
>
> Thanks, but I don't think we can make such changes unconditionally.
> I'm okay with trying this by default, but we should have a Lisp
> variable that would allow to get back to the old behavior. That's
> because if some user complains about some problems, and we think the
> problems are caused by this change, we could tell that user to flip
> the variable and see if the problems go away.
>
> That variable should also be in NEWS.
Revised patch.
From 77fb8097f2ed20f034230a5c61dee00880bbcd24 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miha=20Rihtar=C5=A1i=C4=8D?= <miha@kamnitnik.top>
Date: Mon, 24 May 2021 22:46:47 +0200
Subject: [PATCH] Try to not prioritise reading from lower fds
* src/process.c (wait_reading_process_output): When looping through
fds, continue from where we left off.
(syms_of_process): Vprocess_prioritize_lower_fds: New variable
---
etc/NEWS | 7 +++++++
src/process.c | 27 +++++++++++++++++++++++++--
2 files changed, 32 insertions(+), 2 deletions(-)
diff --git a/etc/NEWS b/etc/NEWS
index 1541b74a3b..cc767c8dc2 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2706,6 +2706,13 @@ the Emacs Lisp reference manual for background.
* Lisp Changes in Emacs 28.1
+++
+** New variable 'process-prioritize-lower-fds'
+When looping through file descriptors to handle subprocess output, try
+to continue from where the previous loop left off instead of always
+beginning from file descriptor zero. Set this variable to t to get
+the old behaviour.
+
+---
** New function 'sxhash-equal-including-properties'.
This is identical to 'sxhash-equal' but accounting also for string
properties.
diff --git a/src/process.c b/src/process.c
index 47a2a6f1a3..7bf55c203e 100644
--- a/src/process.c
+++ b/src/process.c
@@ -5134,6 +5134,7 @@ wait_reading_process_output (intmax_t time_limit, int
nsecs, int read_kbd,
Lisp_Object wait_for_cell,
struct Lisp_Process *wait_proc, int just_wait_proc)
{
+ static int last_read_channel = -1;
int channel, nfds;
fd_set Available;
fd_set Writeok;
@@ -5188,6 +5189,8 @@ wait_reading_process_output (intmax_t time_limit, int
nsecs, int read_kbd,
while (1)
{
bool process_skipped = false;
+ bool wrapped;
+ int channel_start;
/* If calling from keyboard input, do not quit
since we want to return C-g as an input character.
@@ -5722,8 +5725,20 @@ wait_reading_process_output (intmax_t time_limit, int
nsecs, int read_kbd,
d->func (channel, d->data);
}
- for (channel = 0; channel <= max_desc; channel++)
- {
+ channel_start
+ = !NILP (Vprocess_prioritize_lower_fds) ? 0 : last_read_channel + 1;
+
+ for (channel = channel_start, wrapped = false;
+ !wrapped || (channel < channel_start && channel <= max_desc);
+ channel++)
+ {
+ if (channel > max_desc)
+ {
+ wrapped = true;
+ channel = -1;
+ continue;
+ }
+
if (FD_ISSET (channel, &Available)
&& ((fd_callback_info[channel].flags & (KEYBOARD_FD | PROCESS_FD))
== PROCESS_FD))
@@ -5761,6 +5776,7 @@ wait_reading_process_output (intmax_t time_limit, int
nsecs, int read_kbd,
don't try to read from any other processes
before doing the select again. */
FD_ZERO (&Available);
+ last_read_channel = channel;
if (do_display)
redisplay_preserve_echo_area (12);
@@ -8477,6 +8493,13 @@ syms_of_process (void)
The variable takes effect when `start-process' is called. */);
Vprocess_adaptive_read_buffering = Qt;
+ DEFVAR_LISP ("process-prioritize-lower-fds", Vprocess_prioritize_lower_fds,
+ doc: /* If nil, try to not prioritize reading from any process.
+Emacs loops through file descriptors to receive data from subprocesses. After
+accepting output from the first file descriptor with available data, restart
the
+loop from the file descriptor 0 if this option is non-nil. */);
+ Vprocess_prioritize_lower_fds = Qnil;
+
DEFVAR_LISP ("interrupt-process-functions", Vinterrupt_process_functions,
doc: /* List of functions to be called for `interrupt-process'.
The arguments of the functions are the same as for `interrupt-process'.
--
2.31.1
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