From 0a1ed447999d0092e8d0e86729666fc3b4577151 Mon Sep 17 00:00:00 2001 From: Brent Wheeldon Date: Fri, 12 Jan 2018 15:58:04 -0500 Subject: Prevent deadlocks when waiting for connection from pool. When a thread that had the load interlock but was blocked waiting to check a connection out of the connection pool but all of the threads using the available connections were blocked waiting to obtain the load interlock an `ActiveRecord::ConnectionTimeoutError` exception was be thrown by the thread waiting for the connection. When waiting for the connection to check out we should allow loading to proceed to avoid this deadlock. --- activerecord/test/cases/connection_pool_test.rb | 38 +++++++++++++++++++++++++ 1 file changed, 38 insertions(+) (limited to 'activerecord/test/cases') diff --git a/activerecord/test/cases/connection_pool_test.rb b/activerecord/test/cases/connection_pool_test.rb index 9ac03629c3..b02d7fb4fd 100644 --- a/activerecord/test/cases/connection_pool_test.rb +++ b/activerecord/test/cases/connection_pool_test.rb @@ -109,6 +109,44 @@ module ActiveRecord assert_equal connection, t.join.value end + def test_full_pool_blocking_shares_load_interlock + @pool.instance_variable_set(:@size, 1) + + load_interlock_latch = Concurrent::CountDownLatch.new + connection_latch = Concurrent::CountDownLatch.new + + able_to_get_connection = false + able_to_load = false + + thread_with_load_interlock = Thread.new do + ActiveSupport::Dependencies.interlock.running do + load_interlock_latch.count_down + connection_latch.wait + + @pool.with_connection do + able_to_get_connection = true + end + end + end + + thread_with_last_connection = Thread.new do + @pool.with_connection do + connection_latch.count_down + load_interlock_latch.wait + + ActiveSupport::Dependencies.interlock.loading do + able_to_load = true + end + end + end + + thread_with_load_interlock.join + thread_with_last_connection.join + + assert able_to_get_connection + assert able_to_load + end + def test_removing_releases_latch cs = @pool.size.times.map { @pool.checkout } t = Thread.new { @pool.checkout } -- cgit v1.2.3