question about a persistent block

[rhetr]

I've been wanting a VU meter on my bar for a while and finally came across a solution using arecord.I got to writing this block

[vu]
command=arecord -vvv -D pulse_monitor 2>&1 /dev/null | gawk '/#/{ gsub("#","▮"); printf "{\"full_text\":\"%-20s‡\"}\n", $6 }'
interval=persist
format=json

which seems to be working fine except that it only updates every 10 or so seconds, whereas in the terminal it updates in milliseconds .

i wrote a test block to see how fast i can update a block and it seems to be working fine:

[test-ms]
command=while :; do date +'{"full_text": "%3N"}'; done
interval=persist
format=json

so I'm not entirely sure what the problem is.

[rhetr]

reopened and changed issue

[8carlosf]

maybe it is a problem with the buffer on the stdout.. try disabling the buffer

https://serverfault.com/questions/294218/is-there-a-way-to-redirect-output-to-a-file-without-buffering-on-unix-linux/589614

[rhetr]

yes! thanks. I added stdbuf -i0 -o0 -e0 in front of each command and now it works fine.

[rhetr]

not sure if i should open a new issue for this but i just upgraded to v1.5 (also upgraded from ubuntu 16.04 to ubuntu 20.04.1 lol) and now my vu meter keeps flashing. I routed stderr to /tmp/i3blocks.err and this is what I'm seeing:

<7>bar.c:bar_poll_readable:176: [vu-block] readable
<7>line.c:line_parse:65: &7:000: {"full_text":"▮▮▮▮▮▮▯▯▯▯▯▯▯▯▯▯▯▯▯▯"}
<7>block.c:block_update:146: [vu-block] updated successfully
...
<7>bar.c:bar_poll_readable:176: [vu-block] readable
<5>read(7, 1): Resource temporarily unavailable
<7>block.c:block_update:146: [vu-block] updated successfully
...
<7>bar.c:bar_poll_readable:176: [vu-block] readable
<7>line.c:line_parse:65: &7:000: {"full_text":"▮▮▮▮▮▮▮▮▮▯▯▯▯▯▯▯▯▯▯▯"}
<7>block.c:block_update:146: [vu-block] updated successfully
...
<7>bar.c:bar_poll_readable:176: [vu-block] readable
<5>read(7, 1): Resource temporarily unavailable
<7>block.c:block_update:146: [vu-block] updated successfully
...

Why does it keep saying 'resource temporarily unavailable'?

for reference here's the command:

 stdbuf -i0 -o0 -e0 arecord -vvv -B 80000 -D pulse_monitor 2>&1 /dev/null |
    stdbuf -i0 -o0 -e0 gawk '/#/{ gsub("#","▮"); printf "{\"full_text\":\"%-20s\"}\n", substr($6,2) }' |
    stdbuf -i0 -o0 -e0 sed 's/ /▯/g'

you add pulse_monitor to ~/.asoundrc, substituting the device with the one you want to monitor (you can view available sinks with pactl list sinks short):

pcm.pulse_monitor {
  type pulse
  device alsa_output.pci-0000_00_1b.0.analog-stereo.monitor
}

ctl.pulse_monitor {
  type pulse
  device alsa_output.pci-0000_00_1b.0.analog-stereo.monitor
}

[zsugabubus]

Why does it keep saying 'resource temporarily unavailable'?

In a nutshell: because i3blocks’ read mechanism is flawed.

Using strace -fe write -s 50 ./your-command.sh >/dev/null reveals what’s going on (used “x” instead of boxes):

write(1, "{\"full_text\":\"xxxxxxxxxxxxxxxxxxxx\"}", 36) = 36
write(1, "\n", 1)           = 1

EOL is got written as a separate call.

Using stdbuf -oL everywhere fixes it, maybe it will be the solution to your issue too.

[rhetr]

it works thanks! I tried PR 425 but was getting issues when used with this, but when I switched back to master it worked fine.

[zsugabubus]

I can hardly believe that. Tried out just now and got the opposite results. Are you sure?

[rhetr]

yep just tested zsugabubus/drain-stdout again with both -o0 and -oL options and neither worked. master works with -oL like you said.