Re: Emacs Hangs on Filesystem Operations on Stale NFS

[Davis Herring <herring@lanl.gov>]

> signal.alarm(3)
> try: 
>   proc = subprocess.call('stat ' + path,
>                shell=True,
>                stderr=subprocess.PIPE,
>                stdout=subprocess.PIPE)

You're sending SIGALRM to the _parent_, not the (possibly-frozen) 
stat(1) child.  Of course that works; you're just interrupting normal 
pipe I/O with (or wait(2) on) the child.

Emacs can't possibly do all of its file operations in subprocesses.  A 
complete redesign might allow the "process per tab" model used in some 
modern browsers, but that would break much of existing Lisp.  It might 
just be possible to have a "file server process" that could be killed 
and reincarnated as needed, but I wouldn't want to promise much about 
performance (and support for concurrent I/O).

Incidentally, don't mix call() and communicate(), and avoid 
"shell=True", especially when the replacement is easier:

   proc = subprocess.Popen(['stat', path],
                 stderr=subprocess.PIPE,
                 stdout=subprocess.PIPE)

[From a later message:]

> There are plenty of other ways why those file operations might hang.
> For example, [1].
> 
> [1] http://unix.stackexchange.com/questions/63071/local-regular-file-causes-stat-or-ls-l-to-hang

The (single, accepted) answer there says that it was an LDAP issue 
looking up user/group names.  That's not a file operation at all.

Davis

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