Improved service support

	@dustin reported
Trac ID	trac#6813
Type	enhancement
Created	2013-11-05 22:50:29Z

Buildbot is a major consumer of services. A big service tree is created at startup, services come and go during operation, and the service tree gets a major pruning during reconfigs.

All of this turns up some design deficiencies:

• [ticket:5941 services do not start asynchronously], leaving the caller of startService uncertain as to when the service is actually fully started
• the startService and stopService methods do not check whether the service is already running. Neither does MultiService check whether its child services are running before calling their start/stop methods. Related: #4366
• MultiService handles deferreds from stopService incorrectly (this is a straight-up bug, #6790)

There was some discussion of this in #4366, but it appears that the issues cannot be fixed within the current implementation. Maybe they can, or maybe we need a new, alternative implementation.

trac-id__6813 6813
type__enhancement enhancement
reporter__dustin dustin
priority__normal normal
milestone__ 
branch__ 
branch_author__ 
status__new new
resolution__None None
component__core core
keywords__ 
time__1383691829000000 1383691829000000
changetime__1385696679000000 1385696679000000
version__None None
owner__ 
cc__lvh cc__exarkun

Start by reading the service lifecycle and MultiService implementation, then review tickets #5941, #4366, and #6790 for the existing discussion and known behavior. Determine whether asynchronous startup, repeated start/stop checks, and correct stopService deferred handling can fit the current implementation or require an alternative design; done means the service tree handles these lifecycle cases reliably.