A generic server Actors protocol
GenServers allows users to write servers by following three steps:
- Choose a name for your callback module.
- Write your interface functions, e.g.
start(),stop()... - Write the required callback functions:
init,oncall,oncastandterminate.
GenServers provides a generic template for that.
Lets assume you write a small module examples/stack.jl:
module Stack
using GenServers
export start, push, pop, info
# Client (interface)
start(default) = genserver(@__MODULE__, default)
start(name, default) = genserver(@__MODULE__, default, name=name)
push(srv, element) = cast(srv, Val(:push), element)
pop(srv) = call(srv, Val(:pop))
info(srv) = first(query(srv))
reset(srv) = cast(srv, Val(:empty))
stop(srv) = exit!(srv)
# Server (callbacks)
init(stack) = stack
oncast(stack, ::Val{:push}, element) = push!(stack, element)
oncast(stack, ::Val{:empty}) = empty!(stack)
oncall(stack, ::Val{:pop}) = pop!(stack)
endYour module contains only purely sequential code. Now you can do:
julia> include("examples/stack.jl")
Main.Stack
julia> using .Stack
julia> st = start([1,2,3]) # create a stack genserver
Actors.Link{Channel{Any}}(Channel{Any}(sz_max:32,sz_curr:0), 1, :genserver)
julia> info(st)
3-element Array{Int64,1}:
1
2
3
julia> push(st, 4)
Actors.Cast((Val{:push}(), 4))
julia> info(st)
4-element Array{Int64,1}:
1
2
3
4
julia> pop(st)
4This may not look like much, but you may be interested to learn that you just wrote concurrent, thread-safe and distributed code:
julia> Stack.reset(st)
Actors.Cast((Val{:empty}(),))
julia> info(st)
Int64[]
julia> using .Threads
julia> for _ in 1:1000 # push asynchronously
Threads.@spawn begin
push(st, threadid())
end
end
julia> length(info(st))
1000
julia> c = zeros(Int, nthreads());
julia> for i in info(st) # compute the scheduled threads
c[i] += 1
end
julia> c # show them
8-element Array{Int64,1}:
34
49
120
65
146
201
84
301Or with Distributed:
julia> using Distributed
julia> addprocs();
julia> nworkers()
16
julia> @everywhere include("examples/stack.jl")
julia> @everywhere using .Stack
julia> start(:stack, Int[]) # now we register the stack
:stack
julia> info(:stack)
Int64[]
julia> fetch(@spawnat 2 info(:stack))
Int64[]
julia> @everywhere push(:stack, myid())
julia> info(:stack)
17-element Array{Int64,1}:
1
2
7
10
5
⋮
12
17
4
15
14GenServers is part of JuliaActors.
- Paul Bayer
MIT