How Danga::Socket handles asynchronous processing and how to write asynchronous Perlbal plugins
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The document discusses asynchronous programming in Perl and how to write asynchronous plugins for Perlbal using Danga::Socket. Key points include: 1) Danga::Socket provides asynchronous I/O event handling using its main event loop and allows adding I/O watchers and timers. 2) To write asynchronous Perlbal plugins, the main process should be based on Danga::Socket's event loop and use callbacks. The plugin must return 1 and a callback must restart processing in ClientProxy. 3) Perlbal itself may also need patching to work with asynchronous plugins by checking an async completion flag in ClientProxy before running plugins.
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How Danga::Socket handles asynchronous processing and how to write asynchronous Perlbal plugins
- 1. YAPC::Asia 2009 Tokyo 2009/9/10 Gosuke Miyashita
- 2. Speaker Gosuke Miyashita （ mizzy ） Technical manager at paperboy&co. Have most kids in Japan Perl world? 3 kids.Even with Yappo. 4 th kid will be born in November.
- 5. Agenda Asynchronous processing with event driven programming Asynchronous processing with Danga::Socket Overview of Perlbal asynchronous processing How to write asynchronous Perlbal plugins Summary
- 7. Event driven programming A programming paradigm in which the flow of the program is determined by events Counter paradigm of flow-based programming
- 8. Events I/O On I/O read ready or write ready Timers On time passed Signal On getting a signal Child process On child process exit
- 9. Main loop Also called “event loop” On each loop, check that events are occurred or not, and process the events. After process the events, return to the loop and repeat the loop till next events occur This is the flow of asynchronous processing
- 10. Eaxmple of main loop Process timers Wait I/O events Process I/O events Post main loop process
- 12. Events supported by Danga::Socket I/O Timers
- 13. Process I/O events Danga::Socket supports 3 I/O event notification facility kqueue epoll poll Select adequate facility automatically
- 14. Add I/O watcher with Danga::Socket use base ‘Danga::Socket’; sub new { # pass file descripter $self->SUPER::new( $fd ); } sub event_read { # process when $fd is read ready } sub event_write { # procdess when $fd is write ready }
- 15. Add I/O wathcer (pattern 2) Danga::Socket->AddOtherFds( $fd => sub { # process when $fd is read ready }, );
- 16. Add I/O watcher (pattern 3) Danga::Socket::Callback->new( handle => $fd , on_read_ready => sub { # process on read ready }, on_write_ready => sub { # process on write ready }, );
- 17. Add timer watcher with Danga::Socket Danga::Socket->AddTimer( 10, sub { # process after 10 seconds }, }
- 18. Start main loop with Danga::Socket Danga::Socket->EventLoop();
- 19. Main loop(again) Process Timers Wait I/O events Process I/O events Post main loop process
- 21. Perlbal mechanism(as reverse proxy) BackendHTTP ClientProxy TCPListener Client Server ClientProxy Client BackendHTTP Danga::Socket based objects
- 22. Perlbal with a plugin (on start_proxy_request hook) BackendHTTP ClientProxy TCPListener Client Server Plugin::Hoge Target of this session
- 24. Hooks Perlbal has many plugin hooks Explain with start_proxy_request hook in this session
- 25. In case of a synchronous plugin ClientProxy TCPListener Client Server Plugin::Sync Client
- 26. In case of an asynchronous plugin ClientProxy TCPListener Client Server Plugin::Async Client ClientProxy
- 27. How to write asynchronous plugins? Write the main process based on Danga::Socket process within the main loop of Danga::Socket Create Danga::Socket based class Or use Danga::Socket::Callback Or use Danga::Socket::AddTimer Also other libraries need to be non-blocking You can use Gearman::Client::Async with blocking processes
- 28. How to write asynchronous plugins? When finish asynchronous process, go to next phase Call back function Also need to fix Perlbal itself
- 29. Main process of a plugin package My::Drizzle ; use base ‘Danga::Socket’ ; use Net::Drizzle ':constants' ; sub new { $self->SUPER::new($fh); $self->watch_read(1); } sub event_read { # Check db request status and call back when finished }
- 30. Attention You can also use Danga::Socket::Callback You cannot use AddOtherFds() File descriptors added by Add AddOtherFds() are only evaluated at the beginning of the main loop So if already in the main loop, AddOtherFds() are meaningless. You can call epoll_ctl, EV_SET and so on directly, but no portability
- 31. plugin register package Perlbal::Plugin::AsyncDb ; sub register { my ( $class, $svc ) = @_; $svc->register_hook( 'Async' => 'start_proxy_request', &request_db , ); return 1; }
- 32. Call asynchronous process sub request_db { my Perlbal::ClientProxy $client = shift ; My::Drizzle->new( callback => sub { # call back }, ); return 1; # very important! }
- 33. In case of “return 0” BackendHTTP ClientProxy TCPListener Client Server Plugin::Async Go to next step even if Plugin::Async is not finished
- 34. “ return 1” & “call back” BackendHTTP ClientProxy TCPListener Client Plugin::Async Stop the process and go to main loop Server return 1 call back
- 35. Call back function If plugin process finished, ClientProxy must go to the next process(call BackendHTTP) Stopped at the following code of handle_request() : return if $svc->run_hook( 'start_proxy_request', $self ); ClientProxy must start processing from the next of this code
- 36. Call back function my Perlbal::ClientProxy $client = shift ; My::Drizzle->new( callback => sub { $client->{async_complete} = 1; $client->handle_request; }, );
- 37. Patch of ClientProxy::handle_request - return if $svc->run_hook( - 'start_proxy_request', $self - ); + unless ( $self->{async_complete} ) { + return if $svc->run_hook( + 'start_proxy_request', $self + ); + } + $self->{async_complete} = 0;
- 39. Points of asynchronous Perlbal plugins Process within the Danga::Socket main loop return 1 when plugin called Restart ClientProxy process by a call back function when plugin finished Also need to fix Perlbal itself Be careful with order of plugins Following plugins on a same hook are ignored when after a plugin returns 1