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From "Steve Loughran" <stev...@iseran.com>
Subject Re: MP & the <parallel> task (Was Re: Win2K vs Sun)
Date Thu, 28 Feb 2002 18:36:00 GMT

----- Original Message -----
From: "Kyle Adams" <kadams@gfs.com>
To: <ant-user@jakarta.apache.org>
Sent: Thursday, February 28, 2002 05:22
Subject: MP & the <parallel> task (Was Re: Win2K vs Sun)

>I'm still puzzled as to why both Sun boxes ran slower than our baseline
WinNT4 workstation - they had >more physical RAM (1 GB and 2GB versus 512
MB), and a 450 MHz UltraSPARC should be faster in >general than a 750 MHz
Pentium III.

Actually, that final point is not clear, certainly risc cores kick IA to
pieces on FPU stuff, but modern x86 parts are pretty good at integer stuff.
other things like memory access, cache sizes, disk IO and OS all complicate
the picture.

> The ant scripts we use are roughly based on the antgump proposal; a master
build scripts creates a >java process that runs the ant buildfile for each
project.  This java process is forked, so I'm guessing it >would be safe to
run these builds in parallel.  Two pitfalls:

>Problem #1: Projects are dependent upon each other; building two projects
in parallel with one referring >to the other in it's classpath would be bad.

>Solution #1: We can set  up a lib directory ${lib.dir} that contains the
JARs produced in the previous >build, and put these in the classpath for the
current build, thus solving most project dependency >problems.

I'd build a real dependency graph and only run those bits in parallel that
have no dependencies.


>Problem #2: Our various java process (theoretically running in parallel)
won't be writing to the exact >same destination directory (because of
packaging differences), but they will all have the same destdir >for their
respective <javac> tasks (ie, ${classes.dir}).  My understanding is that Ant
automatically adds >this directory to the classpath.  Would this directory
be added before, or after any explicitly added >paths?  If project
dependencies were solved by using files from ${classes.dir} instead of the
stable JARs >in ${lib.dir}, then we could run into problems.

I dont build that way: each project builds to its own dest,a separate
'bundle' project can take these and put them in a central place.


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