Bug 80193

Created attachment 129955 [details] work-in-progress

This patch is subtle because currently creating *any* Database will lock out PageCache forever. The way this works for normal ActiveDOMObjects is that PageCache is locked out only while the object is still around. I need to study the interaction with the DatabaseThread more carefully to see which of these behaviors we want.

Created attachment 130203 [details] checkpoint

So, it turns out that this approach doesn't work because AbstractDatabase can be destructed on either the JavaScript thread or the Database thread. That means we can't inherit from ActiveDOMObject because the ActiveDOMObject destructor might call ScriptExecutionContext::willDestroyActiveDOMObject on the Database thread rather than the JavaScript thread. We probably could solve these problems, if necessary, but the work involved doesn't seem worth the benefit at the moment.

> We probably could solve these problems, if necessary, but the work involved doesn't seem worth the benefit at the moment. Yup, this comment sums up what has been a recurring theme with regard to re-factoring Database stuff to not depend of complex objects that straddle threads (Database and SQLTransaction). Over the years there have be a few occasions where the (large) work involved may have been worth it, but at each crossroad solutions were devised that did not require it. I think the point at which we came closest to biting that bullet was when adding support for Database in workers.