[Scons-dev] Java Development

Fri Aug 1 17:22:39 EDT 2014

SCons Java doesn't need to be that fancy, but I think the root problems can
be solved. The SCons java tool simply doesn't get the love that some of the
other tools get.

I don't have the experience with the code base to know if my ideas are
workable, so I will need some guidance.

On Thu, Jul 31, 2014 at 11:04 PM, Mark A. Flacy <mflacy at verizon.net> wrote:

> On Sunday, July 27, 2014 03:10:34 PM William Deegan wrote:
> > William,
> > On July 25, 2014 at 8:27:02 PM, William Blevins (wblevins001 at gmail.com)
> > wrote:
> >
> > Team,
> >
> > I want to get another thread going for SCons Java development.
> >
> > The SCons Java tool has a ton of error reports on Tigris including 7
> > priority 1 issues.  At the moment, this tool doesn't stand a chance
> against
> > other Java competitors, and not because they are great tools.  I frankly
> > hate ANT.  I have used Java support from SCons and it's seriously
> painful;
> > nothing like the C++ support.  Some other developers have made statements
> > like "No one outside SCons builds Java programs more complicated than
> hello
> > world."  The SCons tool framework is great, and I would really like to
> see
> > the Java toolkit see some love.  It has potential to be a hidden gem,
> and I
> > want help out with this, but I don't have the experience to do this on my
> > own, so firstly I'd like to list some of the biggest hurdles to users
> SCons
> > Java.  I'm not gonna try and propose any solutions at the moment.  I just
> > want to see if I can get the group thinking about the problems.
> >
> > 1. Adding resource files to a jar causes SCons
> > segfault: http://scons.tigris.org/issues/show_bug.cgi?id=2550
> >
> > I have firsthand experience with this bug.  The only way I could figure
> out
> > how to workaround it was to make a separate jar just for resources.
> >
> > 2. Java emitter almost never gets the java output correct.
> >
> > One of the many things I hate about ANT is that ANT is stupid.  It always
> > executes a build even if code is up-to-date and I usually have to
> > explicitly clean.  SCons COULD resolve both problems if the emitters
> > worked.  The only way to get remotely consistent working build is to call
> > Jar( 'buildDir' ) when everyone wants to do Jar( [ 'class1', ...
> 'classN' ]
> > ).
> >
> > 3. Dependencies:
> >
> > SCons does not automatically add classpath items as dependencies.  Why
> do I
> > need to do this manually?  This is what SCons does!  It's the heart and
> > soul!
> >
> > I believe this is because of item #6.
> >
> > 4. Consistency:
> >
> > Classpath tokens (among other items) do not behave the same as other
> > builders. Example: I cannot use "#jar/item.jar" in the classpath without
> > expanding via something like File(...).get_path().
> >
> > 5. Interfaces:
> >
> > Java(...) parameters and internal handling aren't intuitive and only
> handles
> > sources = 'directory' correctly.  It doesn't do lists of java files or
> list
> > of directories in a sane manner.
> > http://scons.tigris.org/issues/show_bug.cgi?id=1772
> >
> > Personally, I don't think that Java and Jar should be separate functions.
> >  How do you get to the classes then?  What about Javah!  I have an idea,
> > but that's outside the scope of this rant.
> >
> > 6. Performance:
> >
> > The dependency structure for Java exposes class files in a way that
> creates
> > tons of false positives.
> >
> > SCons current:
> >
> > classes1 = Java(...)
> >
> > classes2 = Java(...)
> >
> > Depends( classes2, classes1 ) # O( N^2 ) dependency graph with tons of
> false
> > positives
> >
> > SCons if I have anything useful to say about it
> >
> > jar1 = Jar( classes1 )
> >
> > jar2 = Jar( classes2 )
> >
> > Depends( jar2, jar1 ) # O( 1 ) which obviously fails in parallel builds
> > currently.
> >
> > I am currently data mining a production Java codebase to prove my point.
> > Dirk and I have already discussed this issue somewhat; thanks Dirk :)
> >
> > This actually causes the Task Master thread to get blocked on large jars
> > reducing parallel efficiency in builds to None.
> >
> >
> > The main issue here (if I understand SCons’ internals enough) is that
> > SCons’s doing all dependencies on a per file basis. For many types of
> > builds that works fine. For Java (building jars, and other issues) and
> some
> > other types of builds, that’s very inefficient.
> >
> > There’s no “blob” of files where you have N inputs and M outputs, and
> thus
> > you get the N*M arcs in the graph.
> >
> > Currently the only similar but not really similar enough is the Dir()
> Node
> > type.  But that has it’s own problems, which could be solved by a N*M
> type
> > node.
> >
> >
> >
> > Other Java issues could likely be resolved building on top of such a new
> > Node type.
> >
> > Though resolving the anonymous and inner classes in a java file creating
> > more than one class file and what it might be named is also still an
> issue
> > which the scanner and emitter try to solve by parsing the java files and
> > figuring out the proper naming.  This of course is not (as I understand
> it)
> > formally defined as part of the java language and thus is a per compiler
> > implementation detail.
>
> In my opinion, you are wasting your time.
>
> The way java produces artifacts is so different from the model that SCons
> "expects" that you are attempting to cram an elephant down a shrew's
> throat.
> (or attempting to feed a Great White shark with ants, if you prefer) to get
> this to work.
>
> SCons works *great* when there's one output per input, especially when you
> can
> deduce the output name from the input name and little else.  It also works
> great when it is fairly cheap to determine what files a given file depends
> upon.
>
> Sadly, neither of those conditions exist with java source.
>
>
> Between 2003 and 2010, I developed and maintained a python based build tool
> for a Java project that contained ~10K java source files.  It would
> analyse the
> java source files to figure out the package-level compile dependencies and
> then
> send lists of files to be compiled as a unit to a persistent compile
> server (in
> fact, you could run multiple compile servers at once to get a large degree
> of
> parallelism).  It would then analyze the generated class files to see if
> the
> total public/protected interface for the package changed, preventing
> recompiles if all you did was change an implementation detail versus a
> visible
> method or attribute.
>
> You could also register various hooks against packages (such as run rmic)
> if
> the package compiled correctly.  We did some funky stuff with
> autogenerating
> WSDL from java source and then generate client classes from the WSDL and
> compiling those classes also.  Almost all of that was data driven.  It did
> other neat stuff that I don't remember off the top of my head, but I've
> got all
> the source sitting around in various tla/hg repositories.
>
> Nobody uses it any more.  Even me, and I thought about providing some it
> in an
> open source build tool.
>
> For our Windows users, it was faster to nuke the output directories and
> recompile everything in one invocation of javac. (Well, 2 invocations since
> some of the funky stuff was to use the .class files from the first compile
> to
> generate the wsdl and use *that* wsdl to generate java source as part of
> the
> second bulk compile.) Most of the time difference had to do with the way
> the
> python tool talked to the compile processes by sending the list of file
> names
> through a pipe to the other process and then flushing the pipe.  The rest
> had
> to do with the time spent parsing the files (and I maintained a cache of
> parsed
> file information that contained the last mtime of the source files and
> would not
> process a file whose mtime was the same as what was recorded).
>
> For our Linux users (me, for one), it was not quite a wash to change the
> behavior but the delta wasn't enough to worry about.
>
> I'm more than willing to discuss this and also to be proven wrong.
>
> --
> Mark A. Flacy
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>
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