Saturday, September 8, 2007

DBus for filesystem metadata... now working for some types.

And now the DBus magic is complete... getting metadata out of process is quite simple for all clients in an async manner. Clients are nicely isolated from metadata extractors deciding to segv and the API is non blocking... yes it is a little bit slower to do this over the wire (in fact over two wires bidirectionally because the broker actually talks to a worker to do the actual work). But with libferris and its automatic RDF caching the hit is only felt the first time you extract for many of the more expensive operations anyway. On a multicore machine it can actually be faster because you can have many workers attacking files for metadata at once.

I pass the URL back in the signals so that clients don't have to worry about mapping reqid -> url in their process. Such annoying things should be done by the broker for you at the slight cost of sending URLs across process boundaries in both directions.

<node name="/net/sf/witme/libferris/Metadata">
<interface name="net.sf.witme.Libferris.Metadata.Broker">

<method name="asyncGet">
<arg type="s" name="earl" direction="in"/>
<arg type="s" name="name" direction="in"/>
<arg type="i" name="reqid" direction="out"/>

<signal name="asyncGetResult">
<arg type="i" name="reqid" />
<arg type="s" name="earl" />
<arg type="s" name="name" />
<arg type="ay" name="value" />

<signal name="asyncGetFailed">
<arg type="i" name="reqid" />
<arg type="s" name="earl" />
<arg type="i" name="eno" />
<arg type="s" name="ename" />
<arg type="s" name="edesc" />

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