Create an async observer — observeAsync • shinyasync

Like shiny::observe(), but expr runs on a mirai daemon. Dependencies are captured the same way as in reactiveAsync(). When a dependency changes while a task is running, the running task is cancelled and a new one starts.

Usage

observeAsync(
  expr,
  ...,
  globals = NULL,
  label = NULL,
  env = parent.frame(),
  quoted = FALSE
)

Arguments

expr: An expression.
...: Passed to shiny::observe(), e.g. priority, suspended or domain.
globals: A named list of extra objects to make available to expr in the worker.
label: A label for debugging.
env: The environment in which to evaluate expr.
quoted: Is expr a quoted expression?

Value

An observer handle of class "observeAsync": a list with methods status(), cancel(), destroy(), suspend() and resume().

Details

Unlike reactiveAsync(), it does not wait to be read: like shiny::observe(), it runs on the next reactive flush. There is no mode = "queue"; for work that must run once per change, use reactiveAsync(mode = "queue") and read its result.

Errors raised by expr, in the worker or while resolving its reactive dependencies, are reported with message() and leave the observer in status "error" until a dependency changes; the session stays open.