StatusNet queue refactoring landed

Woohoo! After a couple months off and on adjusting the architecture to something that seems to meet our needs, I’ve merged my refactoring of StatusNet’s background queue processing to 0.9.x.

Some of my design notes are up on the wiki, with a couple updates based on tweaks I made from my original plans.

Key items from the commit summary:

Major refactoring of queue handlers to support running multiple sites in one daemon.

Key changes:

  • Initialization code moved from common.php to StatusNet class; can now switch configurations during runtime.
  • As a consequence, configuration files must now be idempotent… Be careful with constant, function or class definitions.
  • Control structure for daemons/QueueManager/QueueHandler has been refactored; the run loop is now managed by IoMaster run via scripts/queuedaemon.php IoManager subclasses are woken to handle socket input or polling, and may cover multiple sites.
  • Plugins can implement notice queue handlers more easily by registering a QueueHandler class; no more need to add a daemon.

The new QueueDaemon runs from scripts/queuedaemon.php:

  • This replaces most of the old *handler.php scripts; they’ve been refactored to the bare handler classes.
  • Spawns multiple child processes to spread load; defaults to CPU count on Linux and Mac OS X systems, or override with –threads=N
  • When multithreaded, child processes are automatically respawned on failure.
  • Threads gracefully shut down and restart when passing a soft memory limit (defaults to 90% of memory_limit), limiting damage from memory leaks.
  • Support for UDP-based monitoring: http://www.gitorious.org/snqmon

Rough control flow diagram:

QueueDaemon -> IoMaster -> IoManager
QueueManager [listen or poll] ->  QueueHandler
XmppManager [ping&  keepalive]
XmppConfirmManager [poll updates]

Todo:

  • Respawning features not currently available running single-threaded.
  • When running single-site, configuration changes aren’t picked up.
  • New sites or config changes affecting queue subscriptions are not yet handled without a daemon restart.
  • SNMP monitoring output to integrate with general tools (nagios, ganglia)
  • Convert XMPP confirmation message sends to use stomp queue instead of polling
  • Convert xmppdaemon.php to IoManager?
  • Convert Twitter status, friends import polling daemons to IoManager
  • Clean up some error reporting and failure modes
  • May need to adjust queue priorities for best perf in backlog/flood cases

Detailed code history available in my daemon-work branch.

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