emacs hangs on scratch buffer for 2 seconds when opening unless key is pressed

[vemacs]

Description: emacs-nox takes an order of magnitude slower to load than on a "real" Ubuntu 14.04 machine with worse specifications, and other text editors

Expected results: emacs should open almost instantaneously, allowing you to edit files

Actual results: emacs hangs on a scratch buffer for about 2 seconds before opening any file. You can "skip" this delay by pressing a random key, but that inserts weird characters at the top of the file (#1505) and isn't something you want to do every time you want to edit a file.

Timings on Bash on Ubuntu on Windows:

[01:22:48] ylin:~ $ time emacs --debug-init --eval '(kill-emacs)'

real    0m2.253s
user    0m0.016s
sys     0m0.203s
[01:23:26] ylin:~ $ time emacs --debug-init -eval '(kill-emacs)' -Q

real    0m2.247s
user    0m0.047s
sys     0m0.141s

Timings with real Ubuntu 14.04.5 installation on a slower computer:

[06:30:04] vemacs@vlt-stor:~ $ time emacs --debug-init --eval '(kill-emacs)'

real    0m0.097s
user    0m0.028s
sys     0m0.024s
[06:30:56] vemacs@vlt-stor:~ $ time emacs --debug-init --eval '(kill-emacs)' -Q

real    0m0.088s
user    0m0.024s
sys     0m0.012s

Windows build number: 15055, this has happened on every Bash on Ubuntu on Windows since 14393.

Steps:

sudo apt-get install emacs24-nox
emacs myfile.txt

Timing commands are provided in the Actual Results section.

[stehufntdev]

Thanks for reporting the issue. Can you please share out an strace with timestamps of the emacs launch?

[vemacs]

I am running strace -r -o emacs_strace.txt emacs --debug-init --eval '(kill-emacs)'.

strace on Bash on Ubuntu on Windows with relative timestamps: http://paste.ubuntu.com/24184468/

The hang appears to be at:

    1.995777 ioctl(3, FIONREAD, [0])   = 0

Here is the strace on a real Ubuntu 14.04 machine that exhibits no hang: http://paste.ubuntu.com/24184497/

[stehufntdev]

Thanks for providing the strace! Looking through the code the only thing I can think of here is waiting with a lock held, but I'll need to get a local repro and report back.

[vemacs]

I upgraded my Bash on Ubuntu on Windows installation to 16.04 and this is still an issue, by the way.

[stehufntdev]

Thanks for the update. Marking this as a bug for tracking.

[vemacs]

Sorry for bothering you guys again, I just took a new strace on 16.04 and the hanging call is slightly different. Here's the strace: http://paste.ubuntu.com/24389133/

Here's the hanging call:

1.995286 poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)

Here's lsof output while the hang is occurring: http://paste.ubuntu.com/24389164/

[stehufntdev]

Not a bother at all, and thanks for the update. Based on the above, we're probably missing an epoll update.

[xarthurx]

I can confirm with this issue. using Emacs25.

Another observation is, it seems the problem is related to FS IO.
emacs open/read files for the first time will be painfully slow.
But after that, reopen/re-read will be fast as long as you don't kill emacs or close bash.exe.

[zachmu]

Issue is still alive and well. Has anyone discovered a workaround?

[HenryGessau]

GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu)
Windows 10 Pro, Version 10.0.19041 Build 19041
WSL2
Still seeing the problem.

[therealkenc]

@HenryGessau what is the output you get from the OP repro on 19041:

[HenryGessau]

@therealkenc I am no longer encountering this issue. Sorry, I don't know when it stopped happening.