diff options
Diffstat (limited to 'activesupport/lib/active_support/concurrency')
| -rw-r--r-- | activesupport/lib/active_support/concurrency/latch.rb | 24 | ||||
| -rw-r--r-- | activesupport/lib/active_support/concurrency/share_lock.rb | 142 |
2 files changed, 150 insertions, 16 deletions
diff --git a/activesupport/lib/active_support/concurrency/latch.rb b/activesupport/lib/active_support/concurrency/latch.rb index 1507de433e..7b8df0df04 100644 --- a/activesupport/lib/active_support/concurrency/latch.rb +++ b/activesupport/lib/active_support/concurrency/latch.rb @@ -1,26 +1,18 @@ -require 'thread' -require 'monitor' +require 'concurrent/atomics' module ActiveSupport module Concurrency - class Latch - def initialize(count = 1) - @count = count - @lock = Monitor.new - @cv = @lock.new_cond - end + class Latch < Concurrent::CountDownLatch - def release - @lock.synchronize do - @count -= 1 if @count > 0 - @cv.broadcast if @count.zero? - end + def initialize(count = 1) + ActiveSupport::Deprecation.warn("ActiveSupport::Concurrency::Latch is deprecated. Please use Concurrent::CountDownLatch instead.") + super(count) end + + alias_method :release, :count_down def await - @lock.synchronize do - @cv.wait_while { @count > 0 } - end + wait(nil) end end end 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..ca48164c54 --- /dev/null +++ b/activesupport/lib/active_support/concurrency/share_lock.rb @@ -0,0 +1,142 @@ +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. + + + def initialize + super() + + @cv = new_cond + + @sharing = Hash.new(0) + @waiting = {} + @exclusive_thread = nil + @exclusive_depth = 0 + end + + # Returns false if +no_wait+ is set and the lock is not + # immediately available. Otherwise, returns true after the lock + # has been acquired. + # + # +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 + if busy?(purpose) + return false if no_wait + + 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 + @exclusive_thread = Thread.current + 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. + # + # 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 + 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?(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 + end +end |