Groovy fixed worker pool with collected errors

import java.util.concurrent.Callable
import java.util.concurrent.Executors

int workers = 4
def tasks = (1..10).collect { int n ->
    ({ -> if (n == 7) throw new IllegalStateException("job $n failed"); n * n } as Callable)
}
def pool = Executors.newFixedThreadPool(workers)
try {
    def futures = pool.invokeAll(tasks)
    futures.each { f ->
        try {
            println "ok ${f.get()}"
        } catch (Exception e) {
            println "err ${e.cause?.message ?: e.message}"
        }
    }
} finally {
    pool.shutdown()
}