question: private static void createTmpFile ( CompletableFuture < NewFile > fileCreation , Path destDir , List < TSData > files ) { LOG . log ( Level . FINE , "starting temporary file creation..." ) ; try { Collections . sort ( files , Comparator . comparing ( null ) ) ; final FileChannel fd = FileUtil . createTempFile ( destDir , "monsoon-" , ".optimize-tmp" ) ; try { final DateTime begin ; try ( ToXdrTables output = new ToXdrTables ( fd , Compression . DEFAULT_OPTIMIZED ) ) { while ( ! files . isEmpty ( ) ) { TSData tsdata = files . remove ( 0 ) ; if ( fileCreation . isCancelled ( ) ) throw new IOException ( "aborted due to canceled execution" ) ; output . addAll ( tsdata ) ; } begin = new DateTime ( output . getHdrBegin ( ) , DateTimeZone . UTC ) ; if ( fileCreation . isCancelled ( ) ) throw new IOException ( "aborted due to canceled execution" ) ; } if ( fileCreation . isCancelled ( ) ) throw new IOException ( "aborted due to canceled execution" ) ; INSTALL_POOL . execute ( null ) ; } catch ( Error | RuntimeException | IOException ex ) { try { fd . close ( ) ; } catch ( Error | RuntimeException | IOException ex1 ) { ex . addSuppressed ( ex1 ) ; } throw ex ; } } catch ( Error | RuntimeException | IOException ex ) { LOG . log ( Level . WARNING , "temporary file for optimization failure" , ex ) ; synchronized ( OUTSTANDING ) { OUTSTANDING . remove ( fileCreation ) ; } fileCreation . completeExceptionally ( ex ) ; } }
target:  The fork-join task that creates a new file. This function creates a temporary file with the result contents, then passes it on to the install thread which will put the final file in place.