1488907 - Unexplained long pause before launching a Firefox instance

Status: NEW

(Testing :: mozregression, defect)

Description

[Botond Ballo [:botond]]

When I run mozregression, there are unexplained long (30+ second) pauses between when it finishes downloading a Firefox package, and when it starts launching it.

For example, here is an excerpt from mozregression output:

 6:03.74 INFO: Narrowed nightly regression window from [2018-03-15, 2018-09-05] (174 days) to [2018-06-07, 2018-09-05] (90 days) (~6 steps left)
 6:03.74 INFO: Pushlog:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=ea21bf3e665d10066b6dce39873de9b353a12e57&tochange=26990836dc5cc3cd1b8027392b79210e71094dc3

 6:03.74 INFO: Using local file: /home/botond/.mozilla/mozregression/persist/2018-07-22--mozilla-central--firefox-63.0a1.en-US.linux-x86_64.tar.bz2
 6:03.76 INFO: Running mozilla-central build for 2018-07-22
 6:47.33 INFO: Launching /tmp/tmpcppd0S/firefox/firefox

When it displays the "Running" message at 6:03, it has already finished downloading the Firefox package. However, it doesn't actually launch it until 6:47, which is 44 seconds (!) later. In the intervening time, nothing appears to be happening. It's not clear what, if anything, mozregression is doing during that time.