The document discusses thread safety in JRuby on Rails applications. It explains that prior to Rails 2.2, each JRuby instance had its own database connection, but newer versions use connection pooling so multiple threads can share database connections through a single JRuby instance. It also covers using ActiveRecord connection pooling and JNDI lookup to configure database connections in a thread-safe way when using JRuby on Rails.

1. JRuby on Rails and
Thread Safety
Naoto Takai
Akasaka.rb / Itochu Techno-Solutions Corp.
29 November 2008

2. ‣ JRuby on Rails and Thread Safety
‣ ActiveRecord and Connection Pooling
‣ JNDI and Connection Pooling

3. ‣ JRuby on Rails and Thread Safety
‣ ActiveRecord and Connection Pooling
‣ JNDI and Connection Pooling

4. Ruby on Rails 2.2 Release Notes

5. Ruby on Rails 2.1 or Prior
Ruby
Process Rails
Instance
Ruby
Process Rails Database
Instance
Ruby
Process Rails
Instance

6. JRuby on Rails 2.1 or Prior
Thread
JRuby
Rails
Instance
Thread
JRuby
Rails Database
Instance
Thread
JRuby
Rails
Instance
Thread

7. One JRuby Instance,
One Database Connection
JRuby
Thread Rails Database
Instance

8. JRuby on Rails 2.2 or Later
Thread
JRuby
Rails
Instance
Thread
JRuby Connection
Rails Database
Instance Pool
Thread
JRuby
Rails
Instance
Thread

9. One JRuby Instance,
Many Database Connections
Thread
JRuby
Rails Database
Instance
Thread
You need less JRuby instances
per database connections.

10. ‣ JRuby on Rails and Thread Safety
‣ ActiveRecord and Connection Pooling
‣ JNDI and Connection Pooling

11. ActiveRecord Connection Pool
ActiveRecord::Base.establish_connection(
:adapter => quot;mysqlquot;,
:username => quot;rootquot;,
:database => quot;databasequot;,
:pool => 5
)

12. Demo Code
10.times do
Thread.new do
ActiveRecord::Base.connection_pool
.with_connection do |c|
ret = c.execute(quot;select connection_id()quot;)
puts quot;Connection ID: %squot; % ret.fetch_row
end
end
end

13. ActiveRecord Connection Pooling (1)
Check-out Connect
Connection
ActiveRecord Database
Pool
Connection

14. ActiveRecord Connection Pooling (2)
Check-out
Connection
ActiveRecord Database
Pool
Connection

15. ActiveRecord Connection Pooling (3)
Wait
Check-out
Connection
ActiveRecord Database
Pool
Connection
Check-out
Check-in
ActiveRecord

16. ‣ JRuby on Rails and Thread Safety
‣ ActiveRecord and Connection Pooling
‣ JNDI and Connection Pooling

17. ‣ JNDI
(Java Naming and Directory Service)
‣ Binding a name to an object.
‣ Look-up the object by name.

18. Using JNDI Look-up
ActiveRecord::Base.establish_connection(
:adapter => quot;jdbcquot;,
:jndi => quot;jdbc/MySQLquot;,
:driver => quot;com.mysql.jdbc.Driverquot;,
:pool => 5
)

19. JNDI Look-up
Look-up
Reference
Connection
Client Database
Pool
Data
Source

20. Java EE Application Server
Connection Pooling
Connect or
Check-out Reconnect
ActiveRecord App Server
ActiveRecord Connection Connection
Pool Pool
Connection Connection
Check-in Disconnect
Database