Erlang and OTP in Action.pdf - Synrc

324
lookup(Key) ->
sc_event:lookup(Key),
case sc_store:lookup(Key) of
{ok, Pid} ->
decompress(sc_element:fetch(Pid)); #1
{error, Reason} ->
{error, Reason}
end.
decompress(Data = {compressed, _, _, _}) -> #2
lzjb:decompress(Data); #3
decompress(Data) ->
Data. #4
Fortunately, we know what compressed data looks like, so we can actually dispatch on that
pattern. You can see that we do this in the head of the decompress function, (annotation #2)
if it looks like compressed data we call lzjb:decompress on it (annotation #3), if it doesn’t we
pass the data back unchanged (annotation #4). To actually use the decompress function,
we call it on every piece of data returned from the cache (annotation #1).
With that our long journey through the world of Drivers, both Port and Linked in, is complete.
We have a fully functioning compression and decompression system integrated into the cache
in a way that is very performant. We can have both uncompressed and compressed data
mixed into the cache without any problem and we have a compression OTP app that we can
use whenever and wherever we need it.
12.4 Summary
In this chapter we looked at the two methods of communication with foreign code that is
available to erlang. We also discussed the caveats of using each of these methods. The use
of the Port Driver is, by far, the preferred solution from a safety standpoint. However, in
some cases speed may be of the essence. In those cases it may be necessary to use a linked
in driver. In either case, you now have the tools you need to create either style of interface.
©Manning Publications Co. Please post comments or corrections to the Author Online forum:
http://www.manning-sandbox.com/forum.jspaforumID=454