Thursday, June 19, 2008

Updates - comm code, etc

I've finally managed to divorce the comm code from the base system. Its proving to be a pain in the butt for a few reasons:

  • The DNS code is involved in the socket connection path - most users just pass a hostname in to the comm connect call and it gets diverted via the ipcache/dns code. Tsk!
  • There's quite a bit of statistics gathering which goes on - the code is very monolithic and the statistics code keeps 5/60 minute histograms as well as raw counters
  • The event loop needs to be sorted out quite a bit better - right now the event loop is still stuck in src/main.c and this needs to change
The statistics gathering and reporting for the network/disk syscalls and events will have to change - I don't feel like trying to make the histogram code more generic and modular. I don't think that Squid should be maintaining the histograms - thats the job for a reporting suite. Squid should just export raw counters for a reporting suite to record and present as appropriate. I'll add in a new cachemgr option to report the "application core" statistics in a machine-parsable manner and leave it at that for now. (As a side-note, I also don't think that Squid should have SNMP code integrated. It should have an easier, cleaner way of grabbing statistics and modifying the configuration and an external SNMP daemon to do SNMP stuff.)

I then need to extract out the main event loop somewhat from src/main.c and turn it into something that can be reused. The main loop handles the following:
  • comm events
  • store dir events
  • timed/immediate registered events
  • signals - which basically just set global variables!
  • checking signal global variables - for rotate, shutdown, etc
I think I'll implement a libevent setup of sorts - I'll implement some methods in libiapp to register callbacks to occur when certain signals are set (sort of like libevent) but the storedir and signal global variable handler will just be functions called in the src/main.c loop. I'd like to implement a Squid-3 like method of registering event dispatchers but I will leave all of that alone until this is all stable and I've done planning into concurrency and SMP.

Its also possible that the reasons for registering dispatchers will go away with a slightly more sensible event abstraction (eg, if I convert the signal handlers to proper events (exactly like libevent!) which get pushed into the head of the event queue and called at the beginning of the next loop iteration - this however assumes the global variables that are set in the current signal handlers are only checked in the main loop and not elsewhere..!)

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