julia server with asynchronous parts and shared memory - asynchronous

Question

I want to create a julia "server" that contains a cached value and serves that when requested and updates the value when an update arrives from other channels
My plan to do this is:
Use julia ZMQ (zeromq) which listens on a REP (reply) socket and delivers the value to any request coming to that REP socket.
Also, the program has a SUB (subscribe) socket that updates the value whenever the socket receives anything
The REP socket blocks using ZMQ.recv.
Maybe the SUB socket does as well, not sure
But basically, both parts need to run independently in a while loop, sharing some memory (variable)
So perhaps this needs to be done using SharedArrays, spawning processes
But I just can't figure out how to do this in code.
E.g. I can #spawn each such process, one has a REP, one has a SUB socket, but I don't know how to get their pid's to create a SharedArray
Can someone help please?
I am also open to different design solutions to solve the problem (basically data is being constantly updated from some source and other programs need to be able to get the most current copy of this data)
Thanks
Imran
EDIT:
I have kind of gotten a simple version to work as follows:
It has 2 independent REP/REQ sockets
The strange thing is that this sometimes works and sometimes after a few calls to readcache() and writecache(41) blocks in either the readcache or the writecache ... but I cannot reproduce, as it sometimes just works smoothly
Is this the correct way of solving this in julia?
using ZMQ
type CT
a::Int
b::String
end
ct = CT(1,"a")
readport = 5551
readproc = #spawn readcacheproc(ct,readport)
writeport = 5552
writeproc = #spawn writecacheproc(ct,writeport)
# test as follows
# readcache() # expect [1 a]
# writecache("test") # expect [4 test]
# readcache() # expect [4 test]
function readcache(port=readport)
ctx=Context()
s=Socket(ctx,REQ)
ZMQ.connect(s,"tcp://localhost:$port")
ZMQ.send(s,"")
println(bytestring(ZMQ.recv(s)))
ZMQ.close(s)
ZMQ.close(ctx)
end
function writecache(value,port=writeport)
ctx=Context()
s=Socket(ctx,REQ)
ZMQ.connect(s,"tcp://localhost:$port")
ZMQ.send(s,"$value")
println(bytestring(ZMQ.recv(s)))
ZMQ.close(s)
ZMQ.close(ctx)
end
function readcacheproc(cache,port=readport)
ctx=Context()
s=Socket(ctx,REP)
ZMQ.bind(s,"tcp://*:$port")
done = false
while !done
msg = bytestring(ZMQ.recv(s)) # actual msg is ignored
ZMQ.send(s,"$(cache.a) $(cache.b)")
end
ZMQ.close(s)
ZMQ.close(ctx)
end
function writecacheproc(cache,port=writeport)
ctx=Context()
s=Socket(ctx,REP)
ZMQ.bind(s,"tcp://*:$port")
done = false
while !done
msg = bytestring(ZMQ.recv(s))
cache.a = length(msg)
cache.b = msg
ZMQ.send(s,"new cache: $(cache.a) $(cache.b)")
end
ZMQ.close(s)
ZMQ.close(ctx)
end

Answer 1

The following seems to work, although I dont know whether this is the best way of solving it
using ZMQ
type CT
a::Int
b::String
end
ct = CT(1,"a")
readport = 5551
readproc = #spawn readcacheproc(ct,readport)
writeport = 5552
writeproc = #spawn writecacheproc(ct,writeport)
# test as follows
# readcache() # expect [1 a]
# writecache("test") # expect [4 test]
# readcache() # expect [4 test]
function readcache(port=readport)
ctx=Context()
s=Socket(ctx,REQ)
ZMQ.connect(s,"tcp://localhost:$port")
ZMQ.send(s,"")
println(bytestring(ZMQ.recv(s)))
ZMQ.close(s)
ZMQ.close(ctx)
end
function writecache(value,port=writeport)
ctx=Context()
s=Socket(ctx,REQ)
ZMQ.connect(s,"tcp://localhost:$port")
ZMQ.send(s,"$value")
println(bytestring(ZMQ.recv(s)))
ZMQ.close(s)
ZMQ.close(ctx)
end
function readcacheproc(cache,port=readport)
ctx=Context()
s=Socket(ctx,REP)
ZMQ.bind(s,"tcp://*:$port")
done = false
while !done
msg = bytestring(ZMQ.recv(s)) # actual msg is ignored
ZMQ.send(s,"$(cache.a) $(cache.b)")
end
ZMQ.close(s)
ZMQ.close(ctx)
end
function writecacheproc(cache,port=writeport)
ctx=Context()
s=Socket(ctx,REP)
ZMQ.bind(s,"tcp://*:$port")
done = false
while !done
msg = bytestring(ZMQ.recv(s))
cache.a = length(msg)
cache.b = msg
ZMQ.send(s,"new cache: $(cache.a) $(cache.b)")
end
ZMQ.close(s)
ZMQ.close(ctx)
end