Add api to send signal to worker nodes

This api will be used by exq_ui to implement unsubscibe all/quiet
feature in the Busy page

lib/exq/api.ex

@@ -541,4 +541,22 @@ defmodule Exq.Api do
   def retry_job(pid, jid) do
     GenServer.call(pid, {:retry_job, jid})
   end
+
+  @doc """
+  Send signal to the given node.
+
+  Expected args:
+    * `pid` - Exq.Api process
+    * `node_id` - node identifier
+    * `signal_name` - Name of the signal.
+
+  Supported Signals
+    * TSTP - unsubscibe from all queues
+
+  Returns:
+    * :ok
+  """
+  def send_signal(pid, node_id, signal_name) do
+    GenServer.call(pid, {:send_signal, node_id, signal_name})
+  end
 end

lib/exq/api/server.ex

@@ -236,6 +236,11 @@ defmodule Exq.Api.Server do
     {:reply, :ok, state}
   end
 
+  def handle_call({:send_signal, node_id, signal_name}, _from, state) do
+    result = JobStat.node_signal(state.redis, state.namespace, node_id, signal_name)
+    {:reply, result, state}
+  end
+
   def terminate(_reason, _state) do
     :ok
   end

lib/exq/redis/job_stat.ex

@@ -103,6 +103,21 @@ defmodule Exq.Redis.JobStat do
     end
   end
 
+  def node_signal(redis, namespace, node_id, signal_name) do
+    key = node_info_key(namespace, node_id)
+    signal_key = "#{key}-signals"
+
+    case Connection.qp(redis, [
+           ["MULTI"],
+           ["LPUSH", signal_key, signal_name],
+           ["EXPIRE", signal_key, 60],
+           ["EXEC"]
+         ]) do
+      {:ok, ["OK", "QUEUED", "QUEUED", [_, 1]]} -> :ok
+      error -> error
+    end
+  end
+
   def node_ids(redis, namespace) do
     Connection.smembers!(redis, nodes_key(namespace))
   end

test/api_test.exs

@@ -99,6 +99,12 @@ defmodule ApiTest do
     assert %Process{pid: ^my_pid_str} = processes
   end
 
+  test "send signal" do
+    assert nil == JobStat.node_ping(:testredis, "test", %Node{identity: "host1", busy: 1})
+    assert :ok = Exq.Api.send_signal(Exq.Api, "host1", "TSTP")
+    assert "TSTP" == JobStat.node_ping(:testredis, "test", %Node{identity: "host1", busy: 1})
+  end
+
   test "jobs when empty" do
     assert {:ok, []} = Exq.Api.jobs(Exq.Api)
   end