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Avoid excessive polling of universal variable file

Browse source 
Reproducible at least on Linux, where the "named pipe" universal
variable notifier is used:

	rm -rf build/test/xdg_config
	XDG_CONFIG_HOME=build/test/xdg_config ./build/fish -c "xterm -e ./build/fish"

The child fish reacts to keyboard input with a noticeable initial
delay.  This is because the universal variable file is polled over
a million times, even when I immediately press Control-D. This polling
prevents readb() from handling keyboard input.
Before commit 939aba02d ("Refactor input_common.cpp:readb"), readb()
reacted to keyboard input even when there were universal variable
notifications.  Restore this behavior, but make sure to call the
universal variable notifier after the new "prepare_to_select" logic.
Maybe the problem is in the notifier but the old behavior was sane.

Fixes the problems described in
7a556ec6f2 (commitcomment-49773677)

Adding "-d uvars-file" to the reproducesr shows that we are checking
the uvar file repeatedly:

	uvar-file: universal log sync
	uvar-file: universal log sync elided based on fast stat()
	uvar-file: universal log no modifications
This commit is contained in:
Johannes Altmanninger 2021-04-25 12:56:34 +02:00 committed by Fabian Homborg
parent c55aa48308
commit b56b230076
2 changed files with 5 additions and 7 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
src/input_common.cpp
View file

@ -57,7 +57,7 @@ enum {
};
using readb_result_t = int;
static readb_result_t readb(int in_fd) {
static readb_result_t readb(int in_fd, bool queue_is_empty) {
assert(in_fd >= 0 && "Invalid in fd");
universal_notifier_t& notifier = universal_notifier_t::default_notifier();
select_wrapper_t fdset;
@ -98,7 +98,9 @@ static readb_result_t readb(int in_fd) {
// This may come about through readability, or through a call to poll().
if (notifier.poll() ||
(fdset.test(notifier_fd) && notifier.notification_fd_became_readable(notifier_fd))) {
return readb_uvar_notified;
if (env_universal_barrier() && !queue_is_empty) {
return readb_uvar_notified;
}
}
// Check stdin.
@ -167,7 +169,7 @@ char_event_t input_event_queue_t::readch() {
return mevt.acquire();
}
readb_result_t rr = readb(in_);
readb_result_t rr = readb(in_, queue_.empty());
switch (rr) {
case readb_eof:
return char_event_type_t::eof;
@ -178,7 +180,6 @@ char_event_t input_event_queue_t::readch() {
break;
case readb_uvar_notified:
env_universal_barrier();
break;
case readb_ioport_notified:

3
tests/checks/tmux-complete.fish
View file

@ -3,9 +3,6 @@
# Don't run this on GitHub Actions since it's flaky.
#REQUIRES: test "$CI" != true
# HACK: THIS IS DISABLED for now, since it doesn't work at the moment.
#REQUIRES: false
# Isolated tmux.
set -g tmpdir (mktemp -d)
set -g tmux tmux -S $tmpdir/.tmux-socket -f /dev/null