Support exiting if configuration is locked by another process

[jlapeyre]

Perhaps print a message and exit.

I am developing tools for Python projects that depend on Julia. I search for Julia installed by juliaup. Detecting if juliaup is not returning because the config file is locked is a bit of a trick. It's not Python-specific of course. Other projects that call juliaup will have to roll their own solution.

This is similar to #253. I good solution to these things might be an API for juliaup that uses machine readable input and output. Maybe json in and out.

[davidanthoff]

There is one API thing already: juliaup api getconfig1. I think your suggestion makes a lot of sense for that, we could for example just add a command line flag --timeout=5 to that particular command, in which case we would only wait for 5 seconds for the lock to free. If we aren't able to acquire the lock, we would just exist with an error return code, maybe?

I also did at some point think about a full bi-directional communication solution based on JSON-RPC, but given that that is much more involved, maybe the simple command line arg would already help?

The caveat is that I need to figure out how to actually specify a timeout in the locking code I use, but hopefully that can be done somehow.

[jlapeyre]

juliaup api getconfig1, yes, this has been very convenient for scripting. I rely on it.

bi-directional communication solution based on JSON-RPC

Agreed, I can see why this would not be the focus of development at the moment. Maybe something simpler, not bidirectional. Along the lines of juliaup api getconfig1. I guess you could go a long way reading and writing single-shot json payloads.

What I am trying to do is read juliaup api getconfig1. That fails if juliaup is, say, downloading a julia. Is it possible/sensible to have only a write lock? For the moment, I run juliaup status first, and read from a pipe. If I get the first words of the error message, then I can take whatever action I need to. Currently, my script errors. But, I could print a warning and skip the action. Maybe a timeout would be good enough. I mean, this shouldn't happen too often. Or maybe a query command juliaup api isconfiglocked, but I suppose you want to be parsimonious with the api. btw, the reason it matters for me is I am trying to make bulletproof scripts for an application where the dependency on Julia is completely hidden from the user.