To reduce risk of stack overflow when catching up with deferred work, make blocking operation runOnMainContext
To reduce risk of stack overflow when catching up with deferred work, make blocking operation runOnMainContext

Summary: Shift wait execution off of a (potential) fiber stack to reduce risk of stack overflows while running deferred work.

Reviewed By: andriigrynenko

Differential Revision: D16643654

fbshipit-source-id: 3ab1fe762b8f93c011cdb926e7689281018f54bc

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly