Vladan Djeric (:vladan) Reporter
	Description • 9 years ago

Currently, TelemetryEnvironment calls into XPCOM methods that perform main-thread I/O to collect configuration info such as the DirectWrite version. 

This is undesirable since it causes main thread jank. We will likely add additional measurements which require file I/O.

Telemetry should be either 1) fetching these measurements itself, off the main thread (using use a PromiseWorker & ctypes) or 2) the underlying code should be refactored to fetch the data off the main thread and return the data asynchronously.

	Vladan Djeric (:vladan) Reporter
	Comment 1 • 9 years ago

There's a couple of other options: 3) put the file-reading functionality in C++ and expose it to a PromiserWorker via WebIDL instead of using ctypes, and 4) extend AsyncFetchTelemetryData to return this info.

I'll leave the decision up to the implementer.

	Georg Fritzsche [:gfritzsche]
	Comment 2 • 9 years ago

We temporarily removed DWriteVersion in bug 1137404 to fix the perf hit, we want to readd that after fixing this here.

	Milan Sreckovic [:milan] (needinfo for best results)
	Comment 3 • 9 years ago

Was this a problem because it was happening during startup, or would it be a lesser problem if it was to happen (the same, main thread i/o blocking way) some time after the startup?

	Vladan Djeric (:vladan) Reporter
	Comment 4 • 9 years ago

We don't want any heavy stuff on the main thread (unless we know the browser is idle -- but we can't rely on that here). We especially don't want heavy stuff on the main thread during startup (i.e. a critical path).

	Deepjyoti Mondal
	Comment 5 • 7 years ago

Hi Georg, I would like to take up this bug. Can yo please provide me some pointers?

	Georg Fritzsche [:gfritzsche]
	Comment 6 • 7 years ago

I don't think this makes for a good starter bug, lets check for other mentored bugs.