Merge pull request #11664 from thedarkone/digestor-thread-safety
AV::Digestor thread safety fixes
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commit
77cf5cfc74
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@ -1,20 +1,40 @@
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require 'thread_safe'
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require 'action_view/dependency_tracker'
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require 'monitor'
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module ActionView
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class Digestor
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cattr_reader(:cache)
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@@cache = ThreadSafe::Cache.new
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@@cache = ThreadSafe::Cache.new
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@@digest_monitor = Monitor.new
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def self.digest(name, format, finder, options = {})
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cache_key = ([name, format] + Array.wrap(options[:dependencies])).join('.')
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@@cache.fetch(cache_key) do
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@@cache[cache_key] ||= nil if options[:partial] # Prevent re-entry
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class << self
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def digest(name, format, finder, options = {})
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cache_key = ([name, format] + Array.wrap(options[:dependencies])).join('.')
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# this is a correctly done double-checked locking idiom
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# (ThreadSafe::Cache's lookups have volatile semantics)
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@@cache[cache_key] || @@digest_monitor.synchronize do
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@@cache.fetch(cache_key) do # re-check under lock
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compute_and_store_digest(cache_key, name, format, finder, options)
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end
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end
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end
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klass = options[:partial] || name.include?("/_") ? PartialDigestor : Digestor
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digest = klass.new(name, format, finder, options).digest
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private
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def compute_and_store_digest(cache_key, name, format, finder, options) # called under @@digest_monitor lock
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klass = if options[:partial] || name.include?("/_")
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# Prevent re-entry or else recursive templates will blow the stack.
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# There is no need to worry about other threads seeing the +false+ value,
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# as they will then have to wait for this thread to let go of the @@digest_monitor lock.
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pre_stored = @@cache.put_if_absent(cache_key, false).nil? # put_if_absent returns nil on insertion
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PartialDigestor
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else
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Digestor
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end
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@@cache[cache_key] = digest # Store the value
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@@cache[cache_key] = digest = klass.new(name, format, finder, options).digest # Store the actual digest
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ensure
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@@cache.delete_pair(cache_key, false) if pre_stored && !digest # something went wrong, make sure not to corrupt the @@cache
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end
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end
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