diff options
| -rw-r--r-- | activesupport/lib/active_support/concurrency/share_lock.rb | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/activesupport/lib/active_support/concurrency/share_lock.rb b/activesupport/lib/active_support/concurrency/share_lock.rb index 2ac278a2f1..ed3345d4dc 100644 --- a/activesupport/lib/active_support/concurrency/share_lock.rb +++ b/activesupport/lib/active_support/concurrency/share_lock.rb @@ -6,12 +6,6 @@ module ActiveSupport # 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 @@ -73,8 +67,10 @@ module ActiveSupport if @exclusive_depth == 0 @exclusive_thread = nil - yield_shares(compatible: compatible) do - @cv.wait_while { @exclusive_thread || eligible_waiters?(compatible) } + if eligible_waiters?(compatible) + yield_shares(compatible: compatible) do + @cv.wait_while { @exclusive_thread || eligible_waiters?(compatible) } + end end @cv.broadcast end @@ -83,7 +79,15 @@ module ActiveSupport def start_sharing(purpose: :share) synchronize do - if @sharing[Thread.current] == 0 && @exclusive_thread != Thread.current && busy_for_sharing?(purpose) + if @sharing[Thread.current] > 0 || @exclusive_thread == Thread.current + # We already hold a lock; nothing to wait for + elsif @waiting[Thread.current] + # We're nested inside a +yield_shares+ call: we'll resume as + # soon as there isn't an exclusive lock in our way + @cv.wait_while { @exclusive_thread } + else + # This is an initial / outermost share call: any outstanding + # requests for an exclusive lock get to go first @cv.wait_while { busy_for_sharing?(purpose) } end @sharing[Thread.current] += 1 @@ -127,6 +131,9 @@ module ActiveSupport end end + # Temporarily give up all held Share locks while executing the + # supplied block, allowing any +compatible+ exclusive lock request + # to proceed. def yield_shares(purpose: nil, compatible: []) loose_shares = previous_wait = nil synchronize do @@ -136,9 +143,9 @@ module ActiveSupport compatible &= previous_wait[1] end @waiting[Thread.current] = [purpose, compatible] - end - @cv.broadcast + @cv.broadcast + end end begin |