Julia TCP select - sockets

Question

I have one problem with TCP connection.
I have made server like:
server = listen(5000)
sock = accept(server)
while isopen(sock)
yes=read(sock,Float64,2)
println(yes)
end
I want that it will continually print [0.0,0.0] when there is nothing to read, otherwise it will print what it reads from server.
This will go to loop(trying to read something), if there is nothing to read or it crashes.
I try to do this with task like:
begin
server = listen(5000)
while true
sock = accept(server)
while isopen(sock)
yes=read(sock,Float64,2)
println(yes)
end
println([0.0,0.0])
end
end
but this will only print what it reads. I'm making connection with other console and ride through consol:
clientside=connect(5000)
write(clientside,[2.0,2.0])
So I'm trying to make server that prints [0.0,0.0], if there is nothing to read and it will print what it reads when there is something to read.
Any good ideas?

Answer 1

Maybe, one strategy to make the server is to run the accept / print block asynchronously (since the accept call blocks the main thread).
Following the tutorial "Using TCP Sockets in Julia", one way to make the server is:
notwaiting = true
server = listen(5000)
while true
if notwaiting
notwaiting = false
# Runs accept async (does not block the main thread)
#async begin
sock = accept(server)
ret = read(sock, Float64, 2)
println(ret)
global notwaiting = true
end
end
println([0.0, 0.0])
sleep(1) # slow down the loop
end
The variable notwaiting makes the async block runs only once per connection (without it, the server runs a kind of "race condition").
Testing it with two calls to the client program, produces the following output:
C:\research\stackoverflow\EN-US>julia s.jl
[0.0,0.0]
[0.0,0.0]
[0.0,0.0]
[0.0,0.0]
[2.0,2.0]
[0.0,0.0]
[0.0,0.0]
[0.0,0.0]
[2.0,2.0]
[0.0,0.0]
[0.0,0.0]
[0.0,0.0]
tested with Julia Version 0.5.0-rc3+0