inability to handle multiprocess target add breaks rustup

[oceanlewis]

Just found this last night while "saving myself some time" during a rustup installation. I wrote a short ruby script to install some architectures to a machine using the following script:

architectures = %w{ <architectures here> }

architectures.each do |_arch|
    out = IO.popen("rustup target add #{_arch}")
    puts out
end

After spinning off a process to download each architecture and promptly failing I went to install each architecture synchronously with:

architectures = %w{ <architectures here> }

architectures.each do |_arch|
    out = `rustup target add #{_arch}`
    puts out
end

and found that I could no longer install any targets, either with a script or as a rustup target add $TARGET from the shell. Deleting the ~/.rustup/tmp directory to fix the issue didn't work. I ended up just deleting the .rustup directory and reinstalling targets synchronously.

Either a lock to prevent multiple occurrences of rustup operating within the same .rustup directory or a check for running rustup processes, each with and a subsequent fail wirg an appropriate error message would fix the issue.

[brson]

Thank you for the report @lewisinc!

Effectively the same problem as #988.

rustup just has no notion of concurrent execution.