question: public Void call ( ) throws Exception { final List < Future < Void > > tasks = new LinkedList < Future < Void > > ( ) ; try { for ( IV < ? , ? > termId : graphs ) { final FutureTask < Void > ft = new FutureTask < Void > ( new DrainIteratorTask ( termId ) ) ; tasks . add ( ft ) ; executor . execute ( ft ) ; } for ( Future < Void > f : tasks ) { f . get ( ) ; } } catch ( Throwable ex ) { for ( Future < Void > f : tasks ) f . cancel ( true ) ; throw new RuntimeException ( ex ) ; } finally { buffer . close ( ) ; } return null ; }
target:  Outer callable submits tasks for execution.