Detecting a failure to execute the process

[mitchellh]

ChildProcess currently doesn't provide a uniform way to detect that there was a failure to execute the given process. Java differs from Linux which differs from Windows.

It would be nice if there was a uniform error I could catch that would signal that ChildProcess wasn't able to start the childprocess... though I'm not sure how to do that easily portably.

In the mean time, I'm building it in to a helper to catch the various exit cases...

For example, executing foo bar baz...

On Linux

The following comes through via the stderr of the child process:

/Users/mitchellh/.rvm/gems/ruby-1.9.3-p0/gems/childprocess-0.2.3/lib/childprocess/unix/process.rb:94:in `exec': No such file or directory - foo (Errno::ENOENT)
    from /Users/mitchellh/.rvm/gems/ruby-1.9.3-p0/gems/childprocess-0.2.3/lib/childprocess/unix/process.rb:94:in `block in launch_process'
    from /Users/mitchellh/.rvm/gems/ruby-1.9.3-p0/gems/childprocess-0.2.3/lib/childprocess/unix/process.rb:83:in `fork'
    from /Users/mitchellh/.rvm/gems/ruby-1.9.3-p0/gems/childprocess-0.2.3/lib/childprocess/unix/process.rb:83:in `launch_process'
    from /Users/mitchellh/.rvm/gems/ruby-1.9.3-p0/gems/childprocess-0.2.3/lib/childprocess/abstract_process.rb:58:in `start'
    from /Users/mitchellh/code/personal/ruby/vagrant/lib/vagrant/util/subprocess.rb:37:in `execute'
    from /Users/mitchellh/code/personal/ruby/vagrant/lib/vagrant/util/subprocess.rb:15:in `execute'
    from test.rb:7:in `<main>'

On Java

The following exception is raised directly in the parent process:

NativeException: java.io.IOException: Cannot run program "foo" (in directory "/Users/mitchellh/code/personal/ruby/vagrant"): error=2, No such file or directory
  launch_process at /Users/mitchellh/.rvm/gems/jruby-1.6.5/gems/childprocess-0.2.3/lib/childprocess/jruby/process.rb:59
           start at /Users/mitchellh/.rvm/gems/jruby-1.6.5/gems/childprocess-0.2.3/lib/childprocess/abstract_process.rb:58
         execute at /Users/mitchellh/code/personal/ruby/vagrant/lib/vagrant/util/subprocess.rb:37
         execute at /Users/mitchellh/code/personal/ruby/vagrant/lib/vagrant/util/subprocess.rb:15
          (root) at test.rb:7

On Windows

(I haven't tested on Windows, sorry, but I imagine it will be different)

[jarib]

Yes, this seems like something we should handle uniformly. I'm not sure exactly how, e.g. on Unix we would need to somehow communicate back to the parent process that the exec() call failed. I may take a look at how OpenJDK does this and adopt that technique.

[jarib]

Setting up a pipe with FD_CLOEXEC and then wait for it to be closed in the parent, or optionally write the error back is probably the right approach for this.

[jarib]

Now released in the 0.2.4 gem.

[mitchellh]

Amazing. I'll put it to use right NOW.

[mitchellh]

Ballin': hashicorp/vagrant@0d2cf4b