[Buildbot] #3225: Open several tabs with chrome makes the UI freeze

[Buildbot trac]

#3225: Open several tabs with chrome makes the UI freeze
-------------------------+-------------------------
Reporter:  tardyp        |      Owner:
    Type:  project-idea  |     Status:  new
Priority:  major         |  Milestone:  0.9.0b1
 Version:  master        |   Keywords:  web, simple
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 Chrome has maximum 6 http connection per server at the same time.

 Our current choice of using SSE is counting one connection. As the SSE
 connection stays open when switching tabs, it is easy to understand that
 you cannot open more than 6 tabs with buildbot on it, and then you are out
 of connections.

 We should use page visibility feature of html5:

 https://developer.mozilla.org/en-
 US/docs/Web/Guide/User_experience/Using_the_Page_Visibility_API

 - detect when the current tab is not visible anymore, and stop the sse
 connection.
 - restart sse connection when the page gets visible again, and reload all
 the data that were watched using the bind() api of buildbotservice.

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Ticket URL: <http://trac.buildbot.net/ticket/3225>
Buildbot <http://buildbot.net/>
Buildbot: build/test automation