io.popen causing luastatus to hang

[intr-cx]

I've been trying to write a widget for displaying the amount of new unread emails. It successfully calculates the number of new mail, but when running it with the lemonbar wrapper and other widgets like cpu-temperature (which also invokes io.popen) the bar will freeze and no longer update.
Here's the script in question;

widget = {
    plugin = 'inotify',
    opts = {
        watch = { [os.getenv("HOME") .. "/.config/mutt/.mailsynclastrun"] = { "attrib" } },
        greet = true
    },
    cb = function()
        local pp = assert(io.popen([[/usr/bin/find /home/intr/.local/share/mail/*/[Ii][Nn][Bb][Oo][Xx]/new/* -type f | wc -l]], 'r'))
        m = pp:read("*a")
        pp:close()
        return '� ' .. m
    end
}

Strangely, the same thing happens when trying to use the bluetooth example widget. I'm positive that io.popen is the function causing it to hang, as I've added a boatload of print statements to narrow it down.
I'm not a lua dev by any means, but I'd love to get this to work. Googling has brought me basically nowhere, so I was wondering if you could explain what I'm doing wrong (or if it's some sort of bug in luastatus.)
Thanks in advance.

[shdown]

Does it also hang if you replace [[/usr/bin/find /home/intr/.local/share/mail/*/[Ii][Nn][Bb][Oo][Xx]/new/* -type f | wc -l]] with echo test?

What versions of Lua, luastatus and lemonbar are you using?

[shdown]

Can you please add io.stderr:write('cb called\n') to the beginning of cb?

Can you run luastatus under strace -f (LUASTATUS="strace -f luastatus" luastatus-lemonbar-launcher …) and paste the full output?

[shdown]

Anyway, I can’t reproduce it here with /tmp/luastatus-test as the file to be watched and the command replaced to date +%s.%N.

[intr-cx]

@shdown Thanks for your reply. The issue seems to happen when using both the cpu-temperature widget (which also uses io.popen) and the mail widget (same with the bluetooth widget.) Below is the output from strace. Perhaps it's related to concurrent calls to popen?

out.txt

[shdown]

What versions of Lua, luastatus and lemonbar are you using?

Does it also hang if you replace [[/usr/bin/find /home/intr/.local/share/mail/*/[Ii][Nn][Bb][Oo][Xx]/new/* -type f | wc -l]] with 'date +%s.%N'?

Can you please add io.stderr:write('cb called\n') to the beginning of cb and io.stderr:write('popen done\n') after popen?

[intr-cx]

Sorry! I forgot to mention those details.

• luastatus-luajit-git from the AUR, r773.8d01bdf-2
• lemonbar-ucs4-git from the AUR, 213.91b444a-1
• Lua 5.4.4

Replacing popen with the date command will spawn the bar showing the date, everything remains responsive until I touch the mailsynclastrun file.

I have also tried switching from the inotify plugin to a simple timer, which will also hang after the second time cb is called.

Adding the io.stderr:write before & after popen will print the first error as follows;

luastatus: error: (lua) mail.lua:8: attempt to call field 'stderr' (a userdata value)
stack traceback:
        mail.lua:8: in function <mail.lua:7>

[intr-cx]

I've also tried different variants of luastatus & lemonbar, namely the vanilla variants without any patches, but the result remains the same.

One thing I noticed is that it's only cpu and mem which end up freezing, the rest (bspwm, pulse, date/time) remains active. Any help would still be appreciated.