private <R> CompletableFuture<R> execute(Callable<R> operation) {
        return CompletableFuture.supplyAsync(() -> {
            try {
                return operation.call();
            } catch (Exception ex) {
                throw new CompletionException(ex);
            }
        }, this.executor);
    }
private < R > CompletableFuture < R > execute ( Callable < R > operation ) { return CompletableFuture . supplyAsync ( ( ) -> { try { return operation . call ( ) ; } catch ( Exception ex ) { throw new CompletionException ( ex ) ; } } , this . executor ) ; }
Executes the given Callable synchronously and invokes cleanup when done.

@param operation    The Callable to execute.