use erlang's queue data-structure for mantaining pending jobs, instea…

…d of a list

lib/toniq/job_concurrency_limiter.ex

@@ -64,15 +64,16 @@ defmodule Toniq.JobConcurrencyLimiter do
   end
 
   defp run_next_pending_job(state, job),      do: run_next_pending_job(state, job, pending_jobs(state, job))
-  defp run_next_pending_job(state, _job, []), do: state
   defp run_next_pending_job(state, job, pending_jobs) do
-    [ first_pending_job | pending_jobs ] = pending_jobs
-
-    state = run_now(state, first_pending_job)
-
-    update_worker_state(state, job,
-      %{ worker_state(state, job) | pending_jobs: pending_jobs }
-    )
+    case :queue.out(pending_jobs) do
+      {:empty, _pending_jobs} ->
+        state
+      {{:value, first_pending_job}, pending_jobs} ->
+        state = run_now(state, first_pending_job)
+        update_worker_state(state, job,
+          %{ worker_state(state, job) | pending_jobs: pending_jobs }
+        )
+    end
   end
 
   defp run_now(state, {job, caller}) do
@@ -83,7 +84,7 @@ defmodule Toniq.JobConcurrencyLimiter do
   defp run_later(state, {job, caller}) do
     worker_state = worker_state(state, job)
     update_worker_state(state, job,
-      %{ worker_state | pending_jobs: worker_state.pending_jobs ++ [ {job, caller} ] }
+      %{ worker_state | pending_jobs: :queue.in({job, caller}, worker_state.pending_jobs) }
     )
   end
 
@@ -109,5 +110,5 @@ defmodule Toniq.JobConcurrencyLimiter do
   defp update_worker_state(state, job, worker_state), do: Map.put(state, job.worker, worker_state)
   defp running_count(state, job),                     do: worker_state(state, job).running_count
   defp pending_jobs(state, job),                      do: worker_state(state, job).pending_jobs
-  defp worker_state(state, job),                      do: Map.get(state, job.worker, %{ pending_jobs: [], running_count: 0 })
+  defp worker_state(state, job),                      do: Map.get(state, job.worker, %{ pending_jobs: :queue.new(), running_count: 0 })
 end