Watched file no longer watched after a change

[sdondley]

Description

If I watch a single file and then make a change to it, the changs is picked up by watchlist. However, the second time a change is made to a file, watchfiles seems to no longer notice. watchfiles seems to work fine when watching a directory.

Example Code

from watchfiles import run_process

def callback(changes):
    print('changes detected:', changes)

def foobar(a, b):
    print('foobar called with:', a, b)

if __name__ == '__main__':
    run_process('single_file', target=foobar, args=(1, 2), callback=callback)

Watchfiles Output

./watch.py
foobar called with: 1 2
changes detected: {(<Change.deleted: 3>, '/home/admin/flask/single_file')}
process already dead, exit code: 0
foobar called with: 1 2

I get no more output as more changes are made to the file.

Operating System & Architecture

Linux-6.1.0-10-cloud-amd64-x86_64-with-glibc2.36
#1 SMP PREEMPT_DYNAMIC Debian 6.1.37-1 (2023-07-03)

Environment

using tmux

Python & Watchfiles Version

python: 3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0], watchfiles: 0.19.0

Rust & Cargo Version

No response

[sdondley]

Just tested this on my mac. Works perfectly and no problems with tmux. Hmm.

I should maybe also note that watchfiles was installed with pipx with things running in some kind of venv for python. I'm not familiar with how that works at all. It's the first I've come across this kind of thing.

[sdondley]

To try to find a workaround, I turned on force_polling:

#!/home/admin/.local/pipx/venvs/watchfiles/bin/python3
from watchfiles import watch

for changes in watch('testfile', force_polling=True):
    print(changes)

It seemed to work for a bit but then I got errors. Here's the output:

{(<Change.modified: 2>, 'testfile')}
{(<Change.modified: 2>, 'testfile')}
{(<Change.modified: 2>, 'testfile')}
{(<Change.modified: 2>, 'testfile')}
{(<Change.modified: 2>, 'testfile')}
Traceback (most recent call last):
  File "/home/admin/flask/./watch.py", line 4, in <module>
    for changes in watch('testfile', force_polling=True):
  File "/home/admin/.local/pipx/venvs/watchfiles/lib/python3.11/site-packages/watchfiles/main.py", line 105, in watch
    raw_changes = watcher.watch(debounce, step, rust_timeout, stop_event)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_rust_notify.WatchfilesRustInternalError: error in underlying watcher: No such file or directory (os error 2) about ["testfile"]

[sdondley]

Doing some more experimenting. Got a different error:

{(<Change.modified: 2>, 'testfile')}
thread 'notify-rs poll loop' panicked at 'internal error: entered unreachable code', /root/.cargo/registry/src/github.com-1ecc6299db9ec823/notify-5.0.0-pre.15/src/poll.rs:206:49
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
  File "/home/admin/test/./watch.py", line 4, in <module>
    for changes in watch('testfile', force_polling=True, raise_interrupt=False):
  File "/home/admin/.local/pipx/venvs/watchfiles/lib/python3.11/site-packages/watchfiles/main.py", line 105, in watch
    raw_changes = watcher.watch(debounce, step, rust_timeout, stop_event)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_rust_notify.WatchfilesRustInternalError: error in underlying watcher: No such file or directory (os error 2) about ["testfile"]

I'm making my edits to the file with vim.

[sdondley]

If I append to the file with a bash command like echo blah >> testfile, things works perfectly.

I suspect this has something to do with how vim modifies/updates files.

[sdondley]

Ok, after searching the issue queue on vim, I found this: #215

Which led me to this: notify-rs/notify#394

So as best I can tell, this watchfiles isn't really going to work for me when watching a single file until some lower level issue in notify gets addressed.

[samuelcolvin]

If the file gets deleted, it's not surprising watching stops.

I would watch the entire directory with rescursive=False, then check which file changes in your own logic.

[sdondley]

What I ended up doing is putting the file in a subdir and symlinking to it from the parent dir and then watching the subdir.

[honglei]

When I use vi to edit and save the watched file, the lib give <Change.deleted: 3>, '/home/uos/conf/send.json', which caused watch stoped . But the file is not removed.
Env: Python3.11.4/watchfiels 0.19/Debian10 arm64