From e2d11970f25890e8baa613bfa33e432bd693627b Mon Sep 17 00:00:00 2001 From: jeffdoering Date: Thu, 13 Jun 2019 11:23:13 -0700 Subject: Make ActiveRecord `ConnectionPool.connections` thread-safe. (#36473) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit * Make ActiveRecord `ConnectionPool.connections` thread-safe. ConnectionPool documentation is clear on the need to synchronize access to @connections but also states that public methods do not require synchronization. Existing code exposed @connections directly via attr_reader. The fix uses synchronize() to lock @connections then returns a copy to the caller using Array.dup(). Includes comments on the connections method that thread-safe access to the connections array does not imply thread-safety of accessing methods on the actual connections. Adds a test-case that modifies the pool using a supported method in one thread while a second thread accesses pool.connections. The test fails without this patch. Fixes #36465. * Update activerecord/test/cases/connection_pool_test.rb [jeffdoering + Rafael Mendonça França] --- .../connection_adapters/abstract/connection_pool.rb | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'activerecord/lib/active_record/connection_adapters') diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb index be804325b3..adb5ae82a0 100644 --- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb +++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb @@ -357,7 +357,7 @@ module ActiveRecord include ConnectionAdapters::AbstractPool attr_accessor :automatic_reconnect, :checkout_timeout, :schema_cache - attr_reader :spec, :connections, :size, :reaper + attr_reader :spec, :size, :reaper # Creates a new ConnectionPool object. +spec+ is a ConnectionSpecification # object which describes database connection information (e.g. adapter, @@ -470,6 +470,21 @@ module ActiveRecord synchronize { @connections.any? } end + # Returns an array containing the connections currently in the pool. + # Access to the array does not require synchronization on the pool because + # the array is newly created and not retained by the pool. + # + # However; this method bypasses the ConnectionPool's thread-safe connection + # access pattern. A returned connection may be owned by another thread, + # unowned, or by happen-stance owned by the calling thread. + # + # Calling methods on a connection without ownership is subject to the + # thread-safety guarantees of the underlying method. Many of the methods + # on connection adapter classes are inherently multi-thread unsafe. + def connections + synchronize { @connections.dup } + end + # Disconnects all connections in the pool, and clears the pool. # # Raises: -- cgit v1.2.3