Re-using the Binding of the XPath::Compiler#compile method would lead to
race conditions, and possibly a memory leak due to the Binding sticking
around for compiled Proc's lifetime.
By using a dedicated class (and its corresponding Binding) we can work
around this. Access to this class is not synchronized as compiled Procs
don't mutate their enclosing environment.
The race condition can be demonstrated using code such as the
following:
xml = <<-EOF
<people>
<person>
<name>Alice</name>
</person>
<person>
<name>Bob</name>
</person>
<person>
<name>Eve</name>
</person>
</people>
EOF
4.times.map do
Thread.new do
10_000.times do
document = Oga.parse_xml(xml)
document.at_xpath('people/person/name').text
end
end
end.each(&:join)
Running this code would result in NoMethodErrors due to "at_xpath"
returning a NilClass opposed to an Oga::XML::Element.
Yorick Peterse