Cancels futures, with the option to interrupt running ones.
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, 4), 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 (NULL) of class MultisessionFuture was canceled, while running on ‘localhost’ (pid 2661694)
## Shut down parallel workers
plan(sequential)