[meta] Rationalize life cycle of plugin classes

[eric@adblockplus.org]

Background

The plugin classes were hacked together originally and have a large amount of ad hoc behavior with their life cycles. There are multiple initialization in multiple places, redundant deinitializations, some problems with objects going out scope still being referenced, etc. This has led to both actual defects as well as convoluted control code to work around poor class design.

The focus here is on classes that have contact directly with IE: the BHO COM class CPluginClass, protocol and media type classes associated with PassthroughAPP, and also the classes whose life cycle are directly dependent upon these.

What to fix

Classes should adhere to some fundamental implementation patterns.

• Paired operations should occur in within natural implementation pairs: constructor / destructor, SetSite() with nullptr / non-nullptr argument, (if required) ATL implementation functions FinalConstruct / FinalRelease.
• The life span of a dependent object is strictly contained within the life span of the object it depends upon.
  • As an important special case, users of a shared resource should hold a shared_ptr (or something containing one) to the resource, ensuring strict life span containment.
• The life span of an event handler should strictly contain the duration of registration for the events it handles.
• Classes with deferred and/or long-running initialization should use a uniform mechanism to determine when the initialization is complete.

Ticket	Status	Resolution	Summary	Owner
#3383	closed	fixed	Clean up browser-site handling in CPluginClass
#3391	reviewing		Detached initialization is defective in corner cases and poorly structured
#3394	new		Factor out status bar into a separate class
#3397	closed	fixed	Correctly initialize entries in the map from threads to tabs
#3432	new		Treat COM events as a resource with RAII
#3433	new		Create effective atomicity between external interfaces such as events and factories
#3456	new		Implementation of CPluginClass::GetAsyncBrowser() makes incorrect assumption about life cycle of site objects