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@mager
Last active Feb 14, 2017
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Consul backend for mutex library
defmodule ConsulMutEx.Backends.ConsulBackend do
@moduledoc """
Use Hashicorp's Consul KV store to acquire and release locks.
[Consul documentation](https://www.consul.io/docs/agent/http/kv.html)
"""
alias Consul.Session
@timeout 1000
@doc """
Initialize this backend.
"""
@spec init() :: :ok
def init() do
:ok
end
@doc """
Acquire a lock.
## Arguments:
* `key`: A key to identify the lock
* `opts`: Options
* `acquire`: The Consul session ID of the lock
* `max_retries`: Maximum number of retries, defaults to 0.
* `cooldown`: Milliseconds to sleep between retries, defaults to 1000.
"""
@spec acquire_lock(String.t, keyword()) :: {:ok, Lock.t} | :error
def acquire_lock(key, opts \\ []) do
do_acquire_lock(key, opts, 0)
end
defp do_acquire_lock(key, opts, retries) do
session = create_session()
if Consul.Kv.put(key, session, acquire: session) do
{:ok, new_lock(key, session)}
else
if retries < Keyword.get(opts, :max_retries, 0) do
:timer.sleep(Keyword.get(opts, :cooldown, @timeout))
do_acquire_lock(key, opts, retries + 1)
else
:error
end
end
end
@doc """
Release a lock.
"""
@spec release_lock(Lock.t) :: :ok
def release_lock(lock) do
if Consul.Kv.put(lock.key, lock.session, release: lock.session) do
:ok
else
:error
end
end
@doc """
Verify a lock.
"""
@spec verify_lock(Lock.t) :: :ok | {:error, any()}
def verify_lock(lock) do
{:ok, resp} = Consul.Kv.fetch(lock.key)
session_id = resp.body
|> List.first
|> Map.get("Session")
cond do
session_id == lock.session -> :ok
is_nil(session_id) -> {:error, nil}
true -> {:error, session_id}
end
end
defp new_lock(key, session) do
%ConsulMutEx.Lock{
key: key,
owner: self(),
session: session
}
end
def create_session() do
{:ok,
%HTTPoison.Response{body: %{"ID" => session_id}}
} = Session.create(%{})
session_id
end
end
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