cancel: Cancel one or more futures

In future: Unified Parallel and Distributed Processing in R for Everyone

Cancel one or more futures

Description

Cancels futures, with the option to interrupt running ones. cancel() is vectorized, i.e. accepts a collection of futures to be canceled.

Usage

cancel(x, interrupt = TRUE, ...)

Arguments

x	A Future, a list, an environment, or a list environment (listenv). Lists and environments may hold a mix of futures and non-future elements, and may be nested, e.g. a list of lists of futures; every future found, at any depth, is canceled.
interrupt	If TRUE, running futures are interrupted, if the future backend supports it.
...	All arguments used by the S3 methods.

Value

cancel() returns (invisibly) x after canceling every Future therein, that is, after flagging each one as "canceled" and possibly interrupting it as well.

Canceling a lazy or a finished future has no effect. Elements of x that are neither futures nor collections of futures are left untouched.

See Also

A canceled future can be reset() to a lazy, vanilla future such that it can be relaunched, possibly on another future backend.

Examples

## Set up two parallel workers
plan(multisession, workers = 2)

## Launch two long running futures
fs <- lapply(c(1, 2), function(duration) {
  future({
    Sys.sleep(duration)
    42
  })
})

## Wait until at least one of the futures is resolved
while (!any(resolved(fs))) Sys.sleep(0.1)

## Cancel futures that are not yet resolved
r <- resolved(fs)
cancel(fs[!r])

## Get the value of the resolved future
f <- fs[r]
v <- value(f)
message("Result: ", v)

## The value of the canceled future is an error
try(v <- value(fs[!r]))

## Shut down parallel workers
plan(sequential)

future documentation built on Oct. 16, 2026, 9:07 a.m.