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Cancel a future

Source: R/core_api-cancel.R
cancel.Rd

Cancels futures, with the option to interrupt running ones.

Usage

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

Arguments

x

A Future.

interrupt

If TRUE, running futures are interrupted, if the future backend supports it.

...

All arguments used by the S3 methods.

Value

cancel() returns (invisibly) the canceled Futures after flagging them as "canceled" and possibly interrupting them as well.

Canceling a lazy or a finished future has no effect.

See also

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

Examples

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

## Launch two long running future
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 the future that is 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)
#> Result: 42

## The value of the canceled future is an error
try(v <- value(fs[!r]))
#> Error : Future (<unnamed-3>) of class MultisessionFuture was canceled (pid 101962) [future <unnamed-3> (dbbff188174479d1afaa51155d0fc60e-3); on dbbff188174479d1afaa51155d0fc60e@hb-x1-2025<101580> at 2025-12-08 13:55:47.907121]

## Shut down parallel workers
plan(sequential)