diff options
Diffstat (limited to 'activesupport/lib/active_support')
3 files changed, 51 insertions, 34 deletions
diff --git a/activesupport/lib/active_support/concurrency/share_lock.rb b/activesupport/lib/active_support/concurrency/share_lock.rb index f1c6230084..ca48164c54 100644 --- a/activesupport/lib/active_support/concurrency/share_lock.rb +++ b/activesupport/lib/active_support/concurrency/share_lock.rb @@ -9,7 +9,7 @@ module ActiveSupport #-- # Note that a pending Exclusive lock attempt does not block incoming # Share requests (i.e., we are "read-preferring"). That seems - # consistent with the behavior of +loose_upgrades+, but may be the + # consistent with the behavior of "loose" upgrades, but may be the # wrong choice otherwise: it nominally reduces the possibility of # deadlock by risking starvation instead. class ShareLock @@ -20,47 +20,48 @@ module ActiveSupport # to upgrade share locks to exclusive. - # If +loose_upgrades+ is false (the default), then a thread that - # is waiting on an Exclusive lock will continue to hold any Share - # lock that it has already established. This is safer, but can - # lead to deadlock. - # - # If +loose_upgrades+ is true, a thread waiting on an Exclusive - # lock will temporarily relinquish its Share lock. Being less - # strict, this behavior prevents some classes of deadlocks. For - # many resources, loose upgrades are sufficient: if a thread is - # awaiting a lock, it is not running any other code. - attr_reader :loose_upgrades - - def initialize(loose_upgrades = false) - @loose_upgrades = loose_upgrades - + def initialize super() @cv = new_cond @sharing = Hash.new(0) + @waiting = {} @exclusive_thread = nil @exclusive_depth = 0 end - # Returns false if +no_wait+ is specified and the lock is not + # Returns false if +no_wait+ is set and the lock is not # immediately available. Otherwise, returns true after the lock # has been acquired. - def start_exclusive(no_wait=false) + # + # +purpose+ and +compatible+ work together; while this thread is + # waiting for the exclusive lock, it will yield its share (if any) + # to any other attempt whose +purpose+ appears in this attempt's + # +compatible+ list. This allows a "loose" upgrade, which, being + # less strict, prevents some classes of deadlocks. + # + # For many resources, loose upgrades are sufficient: if a thread + # is awaiting a lock, it is not running any other code. With + # +purpose+ matching, it is possible to yield only to other + # threads whose activity will not interfere. + def start_exclusive(purpose: nil, compatible: [], no_wait: false) synchronize do unless @exclusive_thread == Thread.current - return false if no_wait && busy? + if busy?(purpose) + return false if no_wait - loose_shares = nil - if @loose_upgrades loose_shares = @sharing.delete(Thread.current) + @waiting[Thread.current] = compatible if loose_shares + + begin + @cv.wait_while { busy?(purpose) } + ensure + @waiting.delete Thread.current + @sharing[Thread.current] = loose_shares if loose_shares + end end - - @cv.wait_while { busy? } if busy? - @exclusive_thread = Thread.current - @sharing[Thread.current] = loose_shares if loose_shares end @exclusive_depth += 1 @@ -106,8 +107,10 @@ module ActiveSupport # +no_wait+ is set and the lock is not immediately available, # returns +nil+ without yielding. Otherwise, returns the result of # the block. - def exclusive(no_wait=false) - if start_exclusive(no_wait) + # + # See +start_exclusive+ for other options. + def exclusive(purpose: nil, compatible: [], no_wait: false) + if start_exclusive(purpose: purpose, compatible: compatible, no_wait: no_wait) begin yield ensure @@ -129,8 +132,9 @@ module ActiveSupport private # Must be called within synchronize - def busy? + def busy?(purpose) (@exclusive_thread && @exclusive_thread != Thread.current) || + @waiting.any? { |k, v| k != Thread.current && !v.include?(purpose) } || @sharing.size > (@sharing[Thread.current] > 0 ? 1 : 0) end end diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb index be03f65e6e..f76ef04f49 100644 --- a/activesupport/lib/active_support/dependencies.rb +++ b/activesupport/lib/active_support/dependencies.rb @@ -37,6 +37,13 @@ module ActiveSupport #:nodoc: Dependencies.interlock.loading { yield } end + # Execute the supplied block while holding an exclusive lock, + # preventing any other thread from being inside a #run_interlock + # block at the same time + def self.unload_interlock + Dependencies.interlock.unloading { yield } + end + # :nodoc: # Should we turn on Ruby warnings on the first load of dependent files? @@ -346,7 +353,7 @@ module ActiveSupport #:nodoc: def clear log_call - Dependencies.load_interlock do + Dependencies.unload_interlock do loaded.clear loading.clear remove_unloadable_constants! diff --git a/activesupport/lib/active_support/dependencies/interlock.rb b/activesupport/lib/active_support/dependencies/interlock.rb index 148212c951..fbeb904684 100644 --- a/activesupport/lib/active_support/dependencies/interlock.rb +++ b/activesupport/lib/active_support/dependencies/interlock.rb @@ -4,21 +4,27 @@ module ActiveSupport #:nodoc: module Dependencies #:nodoc: class Interlock def initialize # :nodoc: - @lock = ActiveSupport::Concurrency::ShareLock.new(true) + @lock = ActiveSupport::Concurrency::ShareLock.new end def loading - @lock.exclusive do + @lock.exclusive(purpose: :load, compatible: [:load]) do yield end end - # Attempt to obtain a "loading" (exclusive) lock. If possible, + def unloading + @lock.exclusive(purpose: :unload, compatible: [:load, :unload]) do + yield + end + end + + # Attempt to obtain an "unloading" (exclusive) lock. If possible, # execute the supplied block while holding the lock. If there is # concurrent activity, return immediately (without executing the # block) instead of waiting. - def attempt_loading - @lock.exclusive(true) do + def attempt_unloading + @lock.exclusive(purpose: :unload, compatible: [:load, :unload], no_wait: true) do yield end end |