On 2012-09-10 14:13, Alan Bateman wrote:
When you say "sub-directory builds" then I think you mean incremental
builds, or "poor-man increment builds" as I call it. I think the
majority of people working in the jdk repository, at least in Oracle,
do this because they know the area and know which make files that
re-build the files that they have changed. Incremental builds are
generally not very reliable but seem to be "good enough" for most
people needs, at least those that aren't doing significant
refactoring. The main motive of course is to be able to re-build in a
few seconds and the #1 goal of any new build system has to be fast
incremental builds.
In the new build system, fast incremental builds of Java code is
dependent on the new "smart javac", which unfortunately has still not
proven stable enough to be enabled by default, even in the experimental
build-infra forest. It is still our hope that it will turn out to be
good enough to be used as default, but I don't want to trust hope alone.
As an interim solution, I have just created the following two shortcuts.
Both of these bypass the proper dependency detection. This means that
make will cut to the chase and recompile faster, but it also means that
you need to take over the responsibility of making sure dependencies are
correct. This is very similar to the "*-only" (e.g. hotspot-only)
targets that are current available in the new build system.
First shortcut is to skip parts of the JDK makefile. By typing e.g.
"make jdk JDK_TARGET=classes", the JDK build will stop after building
the "classes" target (which compiles the majority of the JDK java
files). An even faster, but less safe, version is "make jdk-only
JDK_TARGET=classes-only", which will jump directly to the JDK Makefile,
and only execute the "classes" target. In this way, absolutely no time
is spent before starting to compile Java classes.
Second shortcut is to limit the classes that are recompiled by the JDK
"classes" target. Currently, *all* (more or less) Java classes in the
JDK is recompiled at once. While this speeds up things considerably at a
first time compilation, it makes all subsequent builds take the same
time. By specifying e.g. JDK_FILTER=java/nio, only files in the java/nio
package will get compiled. This is, I think, similar (but not strictly
not identical) to the effect of "sub-directory builds". It is possible
to use an even more fine-grained filter, separated by comma, e.g.
JDK_FILTER=java/nio/channels,java/nio/charset -- the smaller number of
Java files your filter includes, the faster the build will go (more or
less).
These two can of course be combined.
I would like to point out that this is hopefully a temporary solution --
if proper dependency checking and incremental builds get fast enough,
this kind of trickery should not be needed. If this happens, we will
remove the support for these shortcuts since they do carry a risk of
improper builds.
/Magnus
