[webkit-dev] Glib download API change request

[Michael Catanzaro]

Hm, we'll need to investigate this.

Deprecating APIs is easy. Adding newer replacements is often easy. But 
removing APIs is extremely disruptive; we don't want to do that unless 
there is absolutely no viable alternative. It requires an API version 
bump, which requires changes in every application that depends on 
WebKitGTK/WPE even if they don't use the affected API, and new parallel 
packaging in every downstream.

We should try to reimplement the sync APIs using the async APIs so we 
don't have to remove them. The challenge here is we have to do that 
*without* iterating the global RunLoop (otherwise, application 
callbacks will be dispatched at unexpected times, and all manner of 
bugs could occur, including memory corruption and other 
vulnerabilities). So we need to do this using a "private" RunLoop. In 
Linux-specific code, we would do this easily by using GMainContext 
directly; we would create a new GMainContext, push it as 
thread-default, iterate it until the async operation has completed, and 
then pop it, thereby creating a synchronous wrapper around an async 
function call. But I don't think it can be done without changes in 
WebKit's RunLoop. RunLoop does not have any equivalent concept to allow 
temporarily making a different RunLoop the "current" default RunLoop 
for a thread, which is what we need here. It's probably doable, though.

Once before, sometime rather recently (maybe 6-12 months ago?), we gave 
up on doing this properly and landed a patch that iterates the global 
run loop behind the application's back in order to fix some bug. I 
don't remember what particular bug it was, but I was opposed to doing 
that; it's really not safe.

If you're OK with keeping the existing synchronous code around, it 
would be less work to just maintain separate sync and async paths. 
We'll remove all deprecated APIs in the far distant future, next time 
we bump API version; we could add a comment to delete the sync versions 
then.

Michael