register_async: Register an async evaluator

In plumber2: Easy and Powerful Web Servers

Register an async evaluator

Description

plumber supports async request handling in two ways. Either manual by returning a promise from the handler, or automatic through the ⁠@async⁠ tag / async argument in the handler functions. The default evaluator is controlled by the plumber2.async option or the PLUMBER2_ASYNC environment variable.

Usage

register_async(name, fun, dependency = NULL)

show_registered_async()

get_async(name = NULL, ...)

Arguments

name	The name of the evaluator
fun	A function that, upon calling it returns an evaluator taking an expr and envir argument. See the async evaluator functions for examples
dependency	Package dependencies for the evaluator.
...	Arguments passed on to the async function creator

Examples

# Register an async evaluator based on future (the provided mirai backend is
# superior in every way so this is for illustrative purpose)
future_async <- function(...) {
  function(expr, envir) {
    promises::future_promise(
      expr = expr,
      envir = envir,
      substitute = FALSE,
      ...
    )
  }
}
register_async("future", future_async, c("promises", "future"))

plumber2 documentation built on Jan. 20, 2026, 5:06 p.m.