[Scons-users] Batch building includes unchanged targets

[Sean Houghton]

I guess "batch building" is an overloaded phrase.  In my experience batch
building means processing a set of independent items that all share a
common processing pipeline.  In my case I'm submitting the items to be
built to a distributed build system that does a better job scheduling if it
knows about all of the items up front rather than one at a time.

What's the purpose of the targets="$CHANGED_TARGETS" parameter?  There's no
documentation on the batch building so I'm trying to learn all I can by
following the MSVC builder in the source.

I'm looking at possibly using Node.changed() to skip processing
source/target pairs that haven't changed since the last build.  This looks
promising but I don't like bypassing the built in behavior if I don't have
to.


On 25.10.2013 04:40, Sean Houghton wrote:


> I discovered a bug in my batch builder caused by a missing file flush

> which resulted in constant rebuilds.  However, the problem is now that any

> time a single input changes the entire set of sources is passed to the

> batch builder, regardless of change state.

>

>  Thanks for the example...


You're using the batch functionality, which basically means that you give
SCons a black box and say: "Here is my batch builder. It gets N input
files, and has M outputs (=targets)."

With this, SCons will register an NxM dependency for the DAG where each of
the M targets depends on all N sources. This is what you're currently
seeing, and I don't think it's a bug...it's what batch building should do.

If you don't want this behaviour, don't use the batch build but process
your files in single calls (single_source=True). This will also give you
less implicit dependencies overall, so your build usually performs better
regarding speed and memory.

Regards,

Dirk

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