sync_primitives for Elixir

Synchronization Primitives for Elixir, such as CyclicBarrier and CountDownLatch.

These primitives allow you to synchronize multiple Elixir processes using higher-level abstractions than messages. I have found them are very useful in testing agent-based and mutli-process Elixir apps.

Installation

sync_primitives is available on Hex. Add sync_primitives to your list of dependencies in mix.exs:

def deps do
  [{:sync_primitives, "~> 0.1.0"}]
end

Documentation can be found at https://hexdocs.pm/sync_primitives.

CyclicBarrier Usage

1. Start a CyclicBarrier

   barrier = SyncPrimitives.CyclicBarrier.start(2, fn -> IO.puts("barrier action") end)

2. Start the processes you wish to synchronize through a CyclicBarrier.

   1. The first process:

      spawn_link(fn ->
        IO.puts("process 1, before wait")
        SyncPrimitives.CyclicBarrier.await(barrier)
        IO.puts("process 1, after wait")
      end)

   2. Wait for a little bit to see that process 1 won't reach the "after wait" message.

   3. Start the second process:

      spawn_link(fn ->
        IO.puts("process 2, before wait")
        SyncPrimitives.CyclicBarrier.await(barrier)
        IO.puts("process 2, after wait")
      end)

3. All of above will output:

   process 1, before wait
   process 2, before wait
   barrier action
   process 1, after wait
   process 2, after wait
   

4. Remember to stop the barrier

   SyncPrimitives.CyclicBarrier.stop(barrier)

CountDownLatch Usage

1. Start a CountDownLatch

   latch = SyncPrimitives.CountDownLatch.start(2, fn -> IO.puts("latch done") end)

2. Start the process you wish to block until the CountDownLatch is released.

   spawn_link(fn ->
     IO.puts("before wait")
     SyncPrimitives.CountDownLatch.await(latch)
     IO.puts("after wait")
   end)

3. Wait for a little bit to see that the process won't reach the "after wait" message.

4. Countdown enough times for the latch to reach 0.

   SyncPrimitives.CountDownLatch.count_down(latch)
   SyncPrimitives.CountDownLatch.count_down(latch)

5. All of above will output:

   latch done
   after wait
   

6. Remember to stop the latch!

   SyncPrimitives.CountDownLatch.stop(latch)