On 29 January 2014 10:18, Andre Fischer <awf....@gmail.com> wrote: > I would like to report some observations that I made when thinking about > how to make building OpenOffice with one global makefile feasible. It will > probably the last of build related mails in the near future. > > Traditional make uses a top-down approach. It starts with a target, 'all' > by default, and looks at its dependencies. When one of those has to be > made or is newer then the target then the target also has to be made. This > is done recursively and depth-first. Every file on which 'all' has a > direct or indirect dependency has to be checked. If we would build > OpenOffice with one makefile (included makefiles don't count) then that are > a lot of files to check. There are about 9800 cxx files, 3500 c files, > 12000 hxx files, and lot of external headers. Checking the modification > time of so many files is one of the reasons for the delay in , say, sw/ > between starting make and its first action. > > As I don't have all global dependencies in a format that would allow > experimation, I tried how long it would take to get the mtime (time of last > modification) for all files, source, generated, compiled, linked, about > 120000. I wrote a small Java program for that. With a warm cache that > takes about 23s. When run in 4 threads this reduced to less than 8s. > Could be worse. > > But it also could be better because in general there are only a few files > modified, usually files that you modified yourself in an editor. There is > another approach, introduced, as far as I know, by the tup [1] build tool, > that is bottom up. If you had something similar to the oracle of > complexity theory, that gave you the list of modified files since the last > build, you could find the depending files much faster. Faster for two > reasons. Firstly, there is only one path in the dependency tree up towards > the root (while there are many down from the root). Only targets on this > path are affected by the modified file. Secondly, the dependency analysis > is comparatively cheap. The expensive part is to determine the file > modification times. If they where miraculously given then even the > top-down approach would not take noticably longer. > > So I made another experiment to see if such an oracle can be created. > Java 7 has the java.nio.file.WatchService that lets you monitor file > modfifications in one directory. I registered it to all directories in our > source tree (some 16000 directories). With the WatchService in place every > file modification can be recorded and stored for later. On the next build > you only have to check the set of modified files, not all files. > Registering the directory watchers takes a couple of seconds but after > that it does not cause any noticeable CPU activity. Any file modifications > are reported almost at once. I do not have the framework in place to start > a build with this information but I would expect it to be as fast as > compiling the modified files and linking takes. > > The tup website references a paper [2] in which the established top-down > approaches are called alpha alogithms and the new bottom-up approach is > called beta algorithm. Tup has implemented a file modification watcher (in > C or C++) only for Linux. On Windows it just scans all files (for which it > needs a little more time than my Java program, maybe it does not use more > than one thread). > > > This is something that we should keep in mind for when we ever should get > a build solution with global dependencies and this build tool would turn > out to be too slow. > > > If can find the source code of my Java experiments at [3]. If nothing else > you can see an application of the ForkJoinPool that allowed my to write the > parallel file system scan in just a few lines. There is also an > alternative implementation that uses the ExecutorService (with a fixed > thread pool) which needs a few more lines of code. And there is of course > the use of the WatchService. >
Thanks for writing down your observations which I find highly interesting. I hope your stop on writing about build does not include giving your opinion on my ideas in the future as well. For the record the capstone project, and my little hobby project "Build R.I.P." follow a third idea: We have a clear seperation of module build and central (total) build. The module makefile knows how to build the module, and the central makefile knows the relation between modules. The makefile in each module touched a file, and the central makefile only controls that file. But youir idea of watching for changes is very interesting. rgds jan I. > Andre > > > [1] http://gittup.org/tup/ > [2] http://gittup.org/tup/build_system_rules_and_algorithms.pdf > [3] http://people.apache.org/~af/test.zip > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@openoffice.apache.org > For additional commands, e-mail: dev-h...@openoffice.apache.org > >
