Last modified: 2014-11-13 14:47:57 UTC
Our firefox browser tests running on local instances kept complaining of losing connection to the firefox web driver after 45 seconds. We never really managed to figure out the issue and went with throttling the browsertests to ensure that only one run per instance ( https://gerrit.wikimedia.org/r/#/c/155337/ ). Timo proposed a patch to add chromium and a xvfb server on the contint slaves which propose to maintain an xvfb service on display port 99. That is what triggered the race condition warning to me. In mediawiki_selenium we use ruby gems headless defaults: require "headless" headless = Headless.new headless.start Then destroy it: at_exit do headless.destroy end Looking at headless code ( https://github.com/leonid-shevtsov/headless/blob/master/lib/headless.rb ) the default are: * display port 99 * auto picking disabled (since display port is set) * reuses display When the first test start, that boot an xvfb on display port 99. A second test starting in parallel will end up reusing the same display. Imho that would cause a bunch of race conditions between the two browsers being run. mediawiki_selenium should probably be invoked with: Headless.new(autopick: true, reuse: false) We could have that tweakable via env variable such as HEADLESS_DISPLAY, HEADLESS_AUTOPICK and HEADLESS_REUSE.
I can repro the reported behavior consistently in MWV using the following feature/steps. Feature: Parallel Tests Scenario: Process 1 When I wait 10 seconds Then the browser connection should still be alive Scenario: Process 2 When I wait 2 seconds Then the browser connection should still be alive Given(/^I wait (\d+) seconds$/) do |seconds| sleep seconds.to_i end Then(/^the browser connection should still be alive$/) do expect(@browser.execute_script("return true")).to be(true) end And by executing the scenarios in parallel. shell 1$ HEADLESS=true bundle exec cucumber features/test.feature:3 shell 2$ HEADLESS=true bundle exec cucumber features/test.feature:7
Change 164704 had a related patch set uploaded by Dduvall: Additional headless environment variables https://gerrit.wikimedia.org/r/164704
I've submitted a patch that will allow you to provide additional environment variables. Note that simply telling Headless to keep the xvfb process running (destroy_at_exit: false) was enough for my tests to pass. In other words, it appears that the race condition at fault is xvfb shutdown, not a conflict of the display port. However, in case you run into issues screenshot-ing, etc. when using the same display port for multiple test runners, I've also provided an environment variable binding for that.
(In reply to Antoine "hashar" Musso from comment #0) > Timo proposed a patch to add chromium and a xvfb server on the contint > slaves which propose to maintain an xvfb service on display port 99. That > is what triggered the race condition warning to me. > > For the record, my patch uses Xvdb server number 94, not 99. This suspicious may have helped tracked it down, but my deployment did not affect browser tests.
Change 164704 merged by jenkins-bot: Additional headless environment variables https://gerrit.wikimedia.org/r/164704
The patch has been merged and is included in mediawiki_selenium 0.4.1. We have to adjust all repositories to require 0.4.1 and update the Jenkins jobs to set the proper variables. Most probably: export HEADLESS=true export HEADLESS_DESTROY_AT_EXIT=false bundle exec cucumber
