[tor-bugs] #33289 [Applications/rbm]: Expand list of targets more efficiently

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#33289: Expand list of targets more efficiently
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     Reporter:  boklm             |      Owner:  boklm
         Type:  defect            |     Status:  new
     Priority:  Medium            |  Milestone:
    Component:  Applications/rbm  |    Version:
     Severity:  Normal            |   Keywords:  tbb-rbm
Actual Points:                    |  Parent ID:
       Points:                    |   Reviewer:
      Sponsor:                    |
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 dcf has been using a tool called NYTProf to profile rbm:
 https://people.torproject.org/~dcf/graphs/nytprof-
 rbm-20200212-94fce31e/#subs_table

 According to this, rbm has been spending a lot of time in the
 `RBM::get_target` function.

 When the rbm configuration contains something like this:
 {{{
 targets:
   torbrowser-linux-x86_64:
     - linux-x86_64
     - linux
 }}}

 And the list of current targets is `[ 'torbrowser-linux-x86_64' ]`, the
 `RBM::get_targets` function (which is calling `RBM::get_target`) is
 responsible for expanding the list of current targets to `[ 'linux-
 x86_64', 'linux' ]`. It is probably possible to re-implement this in a
 more efficient way.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33289>
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