[OSM-dev] Question running osmosis (node-key-value and way-key-value at the same time)
brett at bretth.com
Wed Jun 24 02:11:24 BST 2009
Karl Newman wrote:
> What's happening there is that the node-key-value and way-key-value
> are ANDed together (which would leave you with only ways which match
> your tags and are composed of nodes tagged place=city), and you want
> an OR instead. You were sort of on the right track with the pipes, but
> what you need to do is use the "tee" function and apply the
> node-key-value filter to one leg of the tee, and apply the
> way-key-value filter to the other leg of the tee, then use the "merge"
> function to join the results. It would look something like this:
> ./osmosis-0.31/bin/osmosis --read-xml file="planet.bz2" --tee
> outputCount=2 outPipe.0="nodes" outPipe.1="ways" --node-key-value
> keyValueList="place.city" inPipe.0="nodes" --way-key-value
> inPipe.0="ways" --merge --write-xml file="basemap.osm"
> I'm not sure if that will work exactly as written. You may need to add
> outPipe arguments to the node-key-value and way-key-value filters and
> then reference them as inPipe.0 and inPipe.1 arguments to the merge task.
You may trigger a deadlock in this situation ... I've been waiting for
somebody to try this out for a long time :-)
While it's possible to construct a pipeline that tees a single dataset
into multiple streams before merging them back together again, it is
problematic from thread synchronisation point of view because the same
input thread is feeding two inputs of another thread. Using a --buffer
task within both paths of the branch may help because it de-couples the
threads somewhat with a buffer.
The --read-xml task creates a thread which passes data into the --tee
task. The --tee task doesn't create a thread, it just uses the existing
thread to pass incoming data to all consumers. The --node-key-value and
--way-key-value also use the existing thread to write to their
destination which in both cases is the --merge task. The --merge task
creates a new thread which reads the incoming data from both of its
inputs, but both inputs are coming from a single thread (ie. the
original --read-xml thread). The --merge thread may read from one
input, then start waiting for a specific value on the the other input
and never receive it.
But if it works let me know. I'm curious :-)
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