pid file handling issue

[Michael Fischer <mfischer@zendesk.com>]

Hi everyone,

While writing a script to determine the success or failure of a
Unicorn reload attempt (without having to parse a log), I noticed that
Unicorn doesn't preserve the timestamp of its pid file.  In other
words, instead of renaming pidfile to pidfile.oldbin (and then back
again if the reload failed), it creates a new pid file for each master
phase change.

This means we cannot simply compare the mtime of the current pidfile
against the time the USR2 signal was given in order to make a
reasonable conclusion.

I tried another method, which was to look at the start time of the
process as reported by ps(1), but on Linux, that time does not come
from the wall clock: it's derived from the number of jiffies since
system boot.  So it's not guaranteed to be accurate, especially if the
wall clock was incorrect at system boot.

Are there any other methods anyone can suggest?  Otherwise, a change
to Unicorn's behavior with respect to pid file maintenance would be
kindly appreciated.

Best regards,

--Michael
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