diff options
Diffstat (limited to 'activesupport')
3 files changed, 243 insertions, 34 deletions
diff --git a/activesupport/lib/active_support/concurrency/share_lock.rb b/activesupport/lib/active_support/concurrency/share_lock.rb new file mode 100644 index 0000000000..f1c6230084 --- /dev/null +++ b/activesupport/lib/active_support/concurrency/share_lock.rb @@ -0,0 +1,138 @@ +require 'thread' +require 'monitor' + +module ActiveSupport + module Concurrency + # A share/exclusive lock, otherwise known as a read/write lock. + # + # https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock + #-- + # 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 + # wrong choice otherwise: it nominally reduces the possibility of + # deadlock by risking starvation instead. + class ShareLock + include MonitorMixin + + # We track Thread objects, instead of just using counters, because + # we need exclusive locks to be reentrant, and we need to be able + # 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 + + super() + + @cv = new_cond + + @sharing = Hash.new(0) + @exclusive_thread = nil + @exclusive_depth = 0 + end + + # Returns false if +no_wait+ is specified and the lock is not + # immediately available. Otherwise, returns true after the lock + # has been acquired. + def start_exclusive(no_wait=false) + synchronize do + unless @exclusive_thread == Thread.current + return false if no_wait && busy? + + loose_shares = nil + if @loose_upgrades + loose_shares = @sharing.delete(Thread.current) + end + + @cv.wait_while { busy? } if busy? + + @exclusive_thread = Thread.current + @sharing[Thread.current] = loose_shares if loose_shares + end + @exclusive_depth += 1 + + true + end + end + + # Relinquish the exclusive lock. Must only be called by the thread + # that called start_exclusive (and currently holds the lock). + def stop_exclusive + synchronize do + raise "invalid unlock" if @exclusive_thread != Thread.current + + @exclusive_depth -= 1 + if @exclusive_depth == 0 + @exclusive_thread = nil + @cv.broadcast + end + end + end + + def start_sharing + synchronize do + if @exclusive_thread && @exclusive_thread != Thread.current + @cv.wait_while { @exclusive_thread } + end + @sharing[Thread.current] += 1 + end + end + + def stop_sharing + synchronize do + if @sharing[Thread.current] > 1 + @sharing[Thread.current] -= 1 + else + @sharing.delete Thread.current + @cv.broadcast + end + end + end + + # Execute the supplied block while holding the Exclusive lock. If + # +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) + begin + yield + ensure + stop_exclusive + end + end + end + + # Execute the supplied block while holding the Share lock. + def sharing + start_sharing + begin + yield + ensure + stop_sharing + end + end + + private + + # Must be called within synchronize + def busy? + (@exclusive_thread && @exclusive_thread != Thread.current) || + @sharing.size > (@sharing[Thread.current] > 0 ? 1 : 0) + end + end + end +end diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb index 664cc15a29..770c845435 100644 --- a/activesupport/lib/active_support/dependencies.rb +++ b/activesupport/lib/active_support/dependencies.rb @@ -12,12 +12,33 @@ require 'active_support/core_ext/kernel/reporting' require 'active_support/core_ext/load_error' require 'active_support/core_ext/name_error' require 'active_support/core_ext/string/starts_ends_with' +require "active_support/dependencies/interlock" require 'active_support/inflector' module ActiveSupport #:nodoc: module Dependencies #:nodoc: extend self + mattr_accessor :interlock + self.interlock = Interlock.new + + # :doc: + + # Execute the supplied block without interference from any + # concurrent loads + def self.run_interlock + Dependencies.interlock.running { 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.load_interlock + Dependencies.interlock.loading { yield } + end + + # :nodoc: + # Should we turn on Ruby warnings on the first load of dependent files? mattr_accessor :warnings_on_first_load self.warnings_on_first_load = false @@ -234,10 +255,12 @@ module ActiveSupport #:nodoc: end def load_dependency(file) - if Dependencies.load? && ActiveSupport::Dependencies.constant_watch_stack.watching? - Dependencies.new_constants_in(Object) { yield } - else - yield + Dependencies.load_interlock do + if Dependencies.load? && ActiveSupport::Dependencies.constant_watch_stack.watching? + Dependencies.new_constants_in(Object) { yield } + else + yield + end end rescue Exception => exception # errors from loading file exception.blame_file! file if exception.respond_to? :blame_file! @@ -325,9 +348,11 @@ module ActiveSupport #:nodoc: def clear log_call - loaded.clear - loading.clear - remove_unloadable_constants! + Dependencies.load_interlock do + loaded.clear + loading.clear + remove_unloadable_constants! + end end def require_or_load(file_name, const_path = nil) @@ -336,39 +361,44 @@ module ActiveSupport #:nodoc: expanded = File.expand_path(file_name) return if loaded.include?(expanded) - # Record that we've seen this file *before* loading it to avoid an - # infinite loop with mutual dependencies. - loaded << expanded - loading << expanded + Dependencies.load_interlock do + # Maybe it got loaded while we were waiting for our lock: + return if loaded.include?(expanded) - begin - if load? - log "loading #{file_name}" - - # Enable warnings if this file has not been loaded before and - # warnings_on_first_load is set. - load_args = ["#{file_name}.rb"] - load_args << const_path unless const_path.nil? + # Record that we've seen this file *before* loading it to avoid an + # infinite loop with mutual dependencies. + loaded << expanded + loading << expanded - if !warnings_on_first_load or history.include?(expanded) - result = load_file(*load_args) + begin + if load? + log "loading #{file_name}" + + # Enable warnings if this file has not been loaded before and + # warnings_on_first_load is set. + load_args = ["#{file_name}.rb"] + load_args << const_path unless const_path.nil? + + if !warnings_on_first_load or history.include?(expanded) + result = load_file(*load_args) + else + enable_warnings { result = load_file(*load_args) } + end else - enable_warnings { result = load_file(*load_args) } + log "requiring #{file_name}" + result = require file_name end - else - log "requiring #{file_name}" - result = require file_name + rescue Exception + loaded.delete expanded + raise + ensure + loading.pop end - rescue Exception - loaded.delete expanded - raise - ensure - loading.pop - end - # Record history *after* loading so first load gets warnings. - history << expanded - result + # Record history *after* loading so first load gets warnings. + history << expanded + result + end end # Is the provided constant path defined? diff --git a/activesupport/lib/active_support/dependencies/interlock.rb b/activesupport/lib/active_support/dependencies/interlock.rb new file mode 100644 index 0000000000..148212c951 --- /dev/null +++ b/activesupport/lib/active_support/dependencies/interlock.rb @@ -0,0 +1,41 @@ +require 'active_support/concurrency/share_lock' + +module ActiveSupport #:nodoc: + module Dependencies #:nodoc: + class Interlock + def initialize # :nodoc: + @lock = ActiveSupport::Concurrency::ShareLock.new(true) + end + + def loading + @lock.exclusive do + yield + end + end + + # Attempt to obtain a "loading" (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 + yield + end + end + + def start_running + @lock.start_sharing + end + + def done_running + @lock.stop_sharing + end + + def running + @lock.sharing do + yield + end + end + end + end +end |