On 10/09/2012 12:26, Magnus Ihse Bursie wrote:
I'd like to start a discussion about the partial builds; what problem
they solve and the best way to solve these problems in the new
build-infra world.
I'm currently investigating on how to handle the equivalence to partial
builds in the new build system. My goal is to see to it that the new
build system does not offer any loss of functionality when developing in
the JDK -- after all, it is supposed to be a improvement, not a step
backwards.
However, the current way of doing partial builds is probably not
suitable for the new build system.
Therefore, I'd like to take a step back and get it down to a bit more of
a functional spec, specifying some common scenarios and requirements on
work.
As I understand it, there are effectively two tricks which are used in
the current build system:
1) "Partial builds". This means that you check out just a single
sub-repo, not the complete forest, and build just that repo. Build
artifacts that are needed from other repos are copied from an external
binary blob, the "import JDK".
2) "Subdirectory builds" (not sure if this trick has any well-known
name). This means that you use the fact that the makefiles are organised
hierarchically, and do e.g. "cd jdk/make/java/nio ; make" to re-build
just the NIO files. For this trick to work, you need to know what
makefile builds the files you are working with.
Trick 1) is used to avoid spending time on building other repos than the
one you're interested in, and trick 2) is used to avoid spending time on
building other parts of the repo, apart from the subset of the repo
you're working with.
Is this a somewhat correct understanding? Am I missing something? Are
there some other reason apart from speeding up the build to do partial
builds? How many users out there are actually using partial builds?
I do partial and subdirectory incremental builds. Typically of the jdk
repo. The main reason is to speed up the development cycle. Subdirectory
incremental builds can complete in a few seconds, and this can aide a
productive development cycle.
I favor partial over full builds as some of the platforms/hardware we
have can take much longer to build all repos, when they are of very
little interest to what I happen to be working on at the time. Yes,
there are risks, I both understand and accept them.
I would like to see some flavor of these supported in the new-build system.
-Chris.
/Magnus
