Erlang and OTP in Action.pdf - Synrc

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Notice at annotation #1 that we have added resource discovery as a dependency.
With the boilerplate out of the way how do we go about getting a hold of the other cache
instances in the cloud of nodes. Not a problem, after going through chapter 8 and building
our resource discovery system this answer should come right to mind. We will simply add an
“I have” or more exactly we add a local resource where the resource_type() is ‘simple_cache’
and the resource_instance() is node(), our local node. We do that simply by calling:
resource_discovery:add_local_resource(simple_cache, node())
The next step is to tell the system about our “I want” or target resource type which is
simple_cache as well. We do this by adding the line:
resource_discovery:add_target_resource_type(simple_cache)
The third and final step to making us simple_cache aware is to add in the call to trade
resources with the rest of the cloud and then to wait a reasonable time for those resources to
be shared. Remember our resource discovery system is very asynchronous. I leave it to the
reader to improve on this timeout model and make the resource discovery system more
synchronous if need be.
resource_discovery:trade_resources(),
timer:sleep(WAIT_FOR_RESOURCES),
This code, predictably I am sure, goes into our sc_app file right after the call to join the
cloud of nodes. This is listed in listing 9.9:
listing 9.9 – sc_app With Resource Discovery
start(_StartType, _StartArgs) ->
ensure_contact(),
sc_resource_discovery:add_local_resource(simple_cache, node()),
sc_resource_discovery:add_target_resource_type(simple_cache),
sc_resource_discovery:trade_resources(),
timer:sleep(WAIT_FOR_RESOURCES),
sc_store:init(),
case sc_sup:start_link() of
{ok, Pid} ->
{ok, Pid};
Error ->
Error
end.
How simple was that! We now know about all the other simple cache instances in our
network and they know about us. Time to replicate.
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