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Constraint Programming Solver
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lib/solver/propagators/propagator_thread.ex
defmodule CPSolver.Propagator.Thread do
alias CPSolver.Variable
alias CPSolver.Common
alias CPSolver.Propagator
alias CPSolver.ConstraintStore
require Logger
@behaviour GenServer
@domain_events Common.domain_events()
@doc """
Create a propagator thread; 'propagator' is a tuple {propagator_mod, args} where propagator_mod
is an implementation of CPSolver.Propagator
Propagator thread is a process that handles life cycle of a propagator.
TODO: details to follow.
"""
def create_thread(space, propagator, opts \\ [id: make_ref()])
def create_thread(
space,
{propagator_mod, propagator_args} = _propagator,
opts
)
when is_atom(propagator_mod) do
{:ok, _thread} =
GenServer.start_link(__MODULE__, [space, propagator_mod, propagator_args, opts])
end
def create_thread(space, propagator, opts) do
[propagator_mod | args] = Tuple.to_list(propagator)
create_thread(space, {propagator_mod, args}, opts)
end
def propagate(thread_pid) when is_pid(thread_pid) do
GenServer.cast(thread_pid, :filter)
end
def dispose(%{thread: pid} = _thread) do
dispose(pid)
end
def dispose(pid) when is_pid(pid) do
(Process.alive?(pid) && GenServer.stop(pid)) || :not_found
end
## Subscribe propagator thread to variables' events
defp subscribe_to_variables(store, thread, variables, events) do
variables
|> Enum.map(fn var -> %{pid: thread, variable: var, events: events} end)
|> then(fn subscriptions -> ConstraintStore.subscribe(store, subscriptions) end)
end
## GenServer callbacks
@impl true
def init([space, propagator_mod, args, opts]) do
store = Keyword.get(opts, :store)
propagator_args =
Enum.map(args, fn
%Variable{} = arg ->
arg
|> Map.put(:store, store)
const ->
const
end)
propagator_vars = propagator_mod.variables(propagator_args)
domain_events =
Keyword.get(opts, :propagate_on, propagator_mod.events()) |> to_domain_events()
subscribe_to_variables(store, self(), propagator_vars, domain_events)
propagator_id = Keyword.get(opts, :id, make_ref())
{:ok,
%{
id: propagator_id,
space: space,
store: store,
stable: false,
propagator_impl: propagator_mod,
propagate_on: domain_events,
filter_on_startup: Keyword.get(opts, :filter_on_startup, true),
args: propagator_args,
unfixed_variables:
Enum.reduce(propagator_vars, MapSet.new(), fn var, acc ->
(Variable.fixed?(var) && acc) || MapSet.put(acc, var.id)
end),
propagator_opts: opts
}, {:continue, :filter}}
end
@impl true
def handle_continue(:filter, %{filter_on_startup: filter?} = data) do
(filter? && filter(data)) || noop(data)
end
@impl true
def handle_cast(:filter, data) do
filter(data)
end
@impl true
def handle_info({:fail, var}, data) do
handle_failure(var, data)
end
def handle_info({:fixed, _var} = fix, data) do
data
|> update_unfixed(fix)
|> filter()
end
def handle_info({domain_change, _var}, data) when domain_change in @domain_events do
if domain_change in data.propagate_on do
filter(data)
else
noop(data)
end
end
### end of GenServer callbacks
defp noop(data) do
{:noreply, data}
end
defp filter(%{propagator_impl: mod, args: args} = data) do
case Propagator.filter(mod, args) do
{:fail, var} ->
handle_failure(var, data)
:stable ->
handle_stable(data)
{:changed, variable_changes} ->
data
|> update_unfixed(variable_changes)
|> filter()
end
end
defp handle_stable(data) do
if entailed?(data) do
handle_entailed(data)
else
publish(data, :stable)
{:noreply, data}
end
end
defp handle_entailed(data) do
publish(data, :entailed)
stop(data)
end
def handle_failure(_var, data) do
stop(data)
end
defp entailed?(%{unfixed_variables: vars} = _data) do
entailed?(vars)
end
defp entailed?(vars) when is_map(vars) do
MapSet.size(vars) == 0
end
defp update_unfixed(data, {_change_type, _var} = change) do
update_unfixed(data, [change])
end
defp update_unfixed(%{unfixed_variables: unfixed} = data, variable_changes)
when is_list(variable_changes) do
## variable_changes is a list of {:change_type, variable_id}
fixed_vars =
Enum.flat_map(variable_changes, fn
{:fixed, var} -> [var]
_ -> []
end)
new_unfixed = MapSet.reject(unfixed, fn v -> v in fixed_vars end)
%{data | unfixed_variables: new_unfixed}
end
defp to_domain_events(propagator_events) do
propagator_events
|> Enum.reduce(
[:fixed],
fn p_event, acc ->
Propagator.to_domain_events(p_event) ++ acc
end
)
|> Enum.uniq()
end
defp publish(%{id: id, space: space} = _data, message) do
send(space, {message, id})
end
defp stop(data) do
{:stop, :normal, data}
end
end