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awormap.ex
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awormap.ex
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defmodule Loom.AWORMap do
@moduledoc """
An add-wins observed-remove map or CRDTs, based on optimized sets.
Compose any CRDT that implements the `Loom.CRDT` protocol. This is awkward by
itself because of the use of copious key-module pairs.
"""
alias Loom.AWORMap, as: M
alias Loom.Dots, as: Dots
alias Loom.CRDT
@type key :: term
@type actor :: term
@type crdt :: term
@type type :: atom | %{__struct__: atom}
@opaque t :: %M{
dots: Dots.t,
keep_delta: boolean,
delta: Dots.t
}
defstruct dots: Dots.new, keep_delta: true, delta: nil
@doc """
Returns a new AWORMap
The identity value of an empty AWORMap is `nil` because of the difficulties
of matching against `%{}`, which is not the equivalent of `[]`.
iex> Loom.AWORMap.new |> Loom.AWORMap.value
nil
"""
@spec new() :: t
def new, do: %M{delta: Dots.new}
@doc """
Returns the currently-running delta of an AWORMap
"""
@spec delta(t) :: t
def delta(%M{delta: delta}), do: %M{dots: delta}
@doc """
You can use this to clear the delta from an AWORMap. Clearing the delta can
help shrink the memory usage of this CRDT.
iex> alias Loom.AWORMap, as: Map
iex> alias Loom.PNCounter, as: Counter
iex> ctr = Counter.new |> Counter.inc(:a, 5) |> Counter.dec(:a, 3)
iex> Map.new |> Map.put(:a, "ctr", ctr) |> Map.clear_delta |> Map.delta == Map.new |> Map.delta
true
"""
@spec clear_delta(t) :: t
def clear_delta(%M{}=m), do: %M{m|delta: Dots.new}
@doc """
Insert a value, and merge it with any that exist already
"""
@spec put(t, actor, key, crdt) :: t
def put(%M{dots: d, delta: d_dots}=m, actor, key, crdt) do
%{__struct__: struct_name} = crdt
new_crdt = CRDT.join(crdt, get(m, key, crdt))
{new_dots, new_d_dots} = {d, d_dots}
|> Dots.remove(fn {dk, %{__struct__: ds}} ->
dk == key && ds == struct_name
end)
|> Dots.add(actor, {key, new_crdt})
%M{dots: new_dots, delta: new_d_dots}
end
@doc """
Delete an entry for a key-module pair
"""
# This really just empties the old CRDT. We'll figure out a way to prune these
# in future time. This might require trying to manage CRDT's via some kind of
# global context, but that breaks internal contiguity needed for delta-CRDT's.
@spec delete(t, key, type) :: t
def delete(set, key, %{__struct__: module}), do: delete(set, key, module)
def delete(%M{dots: d, delta: d_dots}, key, module) do
{new_dots, new_d_dots} = {d, d_dots}
|> Dots.remove(fn {dk, %{__struct__: ds}} ->
dk == key && ds == module
end)
%M{dots: new_dots, delta: new_d_dots}
end
@doc """
Join a map
"""
@spec join(t, t) :: t
def join(%M{dots: d1}=m, %M{dots: d2}) do
%M{m|dots: Dots.join(d1, d2)}
end
@doc """
Empties out an existing map.
iex> alias Loom.CRDT
iex> alias Loom.AWORMap, as: KVMap
iex> KVMap.new
iex> |> KVMap.put(:a, "key", Loom.LWWRegister.new("test"))
iex> |> KVMap.empty
iex> |> CRDT.value
nil
"""
@spec empty(t) :: t
def empty(%M{dots: d, delta: d_dots}=m) do
{new_d, new_d_dots} = Dots.empty({d, d_dots})
%M{m|dots: new_d, delta: new_d_dots}
end
@doc """
Get a value for a key-module pair
"""
@spec get(t, key, type) :: term
def get(map, key, module) when is_atom(module), do: get(map, key, struct(module))
def get(%M{dots: d}, key, %{__struct__: module}=old_crdt) do
(for {_,{k, crdt}} <- Dots.dots(d),
k == key,
module == get_structname(crdt),
do: crdt)
|> Enum.reduce(old_crdt, &CRDT.join(&1, &2))
end
defp get_structname(%{__struct__: module}), do: module
@doc """
Get a value's value for a key-module pair
"""
@spec get_value(t, key, type) :: term
def get_value(map, key, module), do: get(map, key, module) |> CRDT.value
@doc """
Returns the set of all key-module pairs
"""
@spec keys(t) :: [{key,type}]
def keys(%M{dots: d}) do
(for {_,{k, %{__struct__: module}}} <- Dots.dots(d), do: {k, module})
|> Enum.uniq
end
@doc """
Tests to see if the CRDT is empty.
This is used in compositing CRDT's because CRDT's with dots might actually be
full of empty CRDT's, because we have to remain robust against undead updates
that want to feast on our collective brains. Time is a flat circle.
iex> alias Loom.CRDT
iex> alias Loom.AWORMap, as: KVMap
iex> KVMap.new |> KVMap.empty?
true
"""
def empty?(%M{dots: d}) do
# (Dots.dots(d) |> Enum.filter(fn {_, {_,crdt}} -> CRDT.empty?(crdt) end) |> Enum.count) == 0
# TODO: implement empty:
(Dots.dots(d) |> Enum.count) == 0
end
@doc """
Checks if a key-module pair exists in the map already for the key.
"""
@spec has_key?(t, key, module) :: boolean
def has_key?(%M{dots: d}, key, module) do
Dots.dots(d) |> Enum.any?(fn
{_,{k, %{__struct__: m}}} when k == key and m == module -> true
_ -> false
end)
end
@doc """
Returns a map of values for key-module pairs
"""
@spec value(t) :: [{key,term}] | nil
def value(%M{dots: d}) do
res = Enum.reduce(Dots.dots(d), %{}, fn {_, {k, %{__struct__: module}=crdt}}, values ->
Dict.update(values, {k, module}, crdt, &CRDT.join(crdt,&1))
end)
|> Enum.map(fn {k,v} -> {k, CRDT.value(v)} end)
|> Enum.into %{}
case map_size(res) do
0 -> nil
_ -> res
end
end
end
defimpl Loom.CRDT, for: Loom.AWORMap do
alias Loom.AWORMap, as: KVSet
@doc """
Returns a description of the operations that this CRDT takes.
Updates return a new CRDT, reads can return any natural datatype. This register
returns a value.
"""
def ops(_crdt) do
[
update: [
delete: [:key, :value_type],
put: [:actor, :key, :value]
],
read: [
get: [:value],
keys: [],
has_key: [],
value: []
]
]
end
@doc """
Applies a CRDT to a counter in an abstract way.
This is for ops-based support.
iex> alias Loom.CRDT
iex> alias Loom.LWWRegister
iex> bar = LWWRegister.new("bar")
iex> wtf = LWWRegister.new("wtf")
iex> Loom.AWORMap.new
...> |> CRDT.apply({:put, :a, "foo", bar})
...> |> CRDT.apply({:put, :a, "omg", wtf})
...> |> CRDT.apply({:delete, "omg", LWWRegister})
...> |> CRDT.apply(:value)
%{{"foo", Loom.LWWRegister} => "bar"}
iex> alias Loom.CRDT
iex> Loom.AWORMap.new |> CRDT.apply({:has_key, :none, Loom.LWWRegister})
false
iex> alias Loom.CRDT
iex> Loom.AWORMap.new |> CRDT.apply({:get_value, :none, Loom.LWWRegister})
nil
iex> alias Loom.CRDT
iex> Loom.AWORMap.new |> CRDT.apply({:get, :none, Loom.LWWRegister})
%Loom.LWWRegister{}
iex> alias Loom.CRDT
iex> Loom.AWORMap.new |> CRDT.apply(:keys)
[]
"""
def apply(crdt, {:put, actor, key, value}) do
KVSet.put(crdt, actor, key, value)
end
def apply(crdt, {:delete, key, module}) do
KVSet.delete(crdt, key, module)
end
def apply(crdt, {:get, key, module}), do: KVSet.get(crdt, key, module)
def apply(crdt, {:get_value, key, module}), do: KVSet.get_value(crdt, key, module)
def apply(crdt, {:has_key, key, module}), do: KVSet.has_key?(crdt, key, module)
def apply(crdt, :keys), do: KVSet.keys(crdt)
def apply(crdt, :value), do: KVSet.value(crdt)
@doc """
Joins 2 CRDT's of the same type.
2 different types cannot mix (yet).
iex> alias Loom.CRDT
iex> alias Loom.MVRegister, as: Reg
iex> test_a = Reg.new |> Reg.set(:a, 1)
iex> test_b = Reg.new |> Reg.set(:b, 2)
iex> a = Loom.AWORMap.new |> CRDT.apply({:put, :a, :test, test_a})
iex> b = Loom.AWORMap.new |> CRDT.apply({:put, :b, :test, test_b})
iex> CRDT.join(a,b) |> CRDT.apply(:value)
%{{:test, Loom.MVRegister} => [1,2]}
"""
def join(a, b), do: KVSet.join(a, b)
@doc """
Returns the most natural primitive value for a set, a list.
iex> Loom.AWORMap.new |> Loom.CRDT.value
nil
"""
def value(crdt), do: KVSet.value(crdt)
end