I have been having so much trouble with long calculations in shiny and multiple users accessing the app and experiencing lags and locks while long processes are running.
I've came across this package, and sounds promising!
I haven't tried it yet. Is it stable? Do you have any estimation of realease date? I suppose it's still been developed and might change in near future, so I don't want to start including it if will change its behaviour in next weeks.
In it he gives an estimated release date on CRAN at the end of the year 2017.
The code at https://github.com/rstudio/promises is said to be "beta quality" for now (that was last month, but there hasn't been that many commits since).
I can confirm this is a top priority for @jcheng, but it is not yet baked into Shiny. We'll have our next release when that's all ready and announce it in our blog, so you can just stay tuned there. I wouldn't start using this yet for any apps that are supposed to go into production in the near future, but it is upcoming!