Crew worker hook

[multimeric]

Prework

• [x] Read and agree to the Contributor Code of Conduct and contributing guidelines.
• [x] If there is already a relevant issue, whether open or closed, comment on the existing thread instead of posting a new issue.
• [x] New features take time and effort to create, and they take even more effort to maintain. So if the purpose of the feature is to resolve a struggle you are encountering personally, please consider first posting a "trouble" or "other" issue so we can discuss your use case and search for existing solutions first.
• [x] Format your code according to the tidyverse style guide.

Proposal

Frequently I want the ability to monitor crew workers, for example by running strace. However, crew doesn't seem to provide a hook for doing this.

I propose a new argument to the controller functions such as crew_controller_local() called something like worker_hook, which is a function that takes the processx process object. The hook would run as part of the worker initialisation. This would allow me to set up appropriate monitoring.

For example:

controller <- crew_controller_local(
    worker_hook = function(process){
        pid <- process$get_pid()
        system2("strace", c("-p", pid), stdout="strace_log.txt")
    }
)

[wlandau]

Sorry, I feel this level of flexibility is not usually going to be necessary for most use cases. You can get the processx handles from controller$launcher$workers$handle.