1 files changed, 136 insertions, 0 deletions
diff --git a/actioncable/lib/action_cable/connection/stream_event_loop.rb b/actioncable/lib/action_cable/connection/stream_event_loop.rb
new file mode 100644
index 0000000000..d95afc50ba
--- /dev/null
+++ b/actioncable/lib/action_cable/connection/stream_event_loop.rb
@@ -0,0 +1,136 @@
+# frozen_string_literal: true
+
+require "nio"
+require "thread"
+
+module ActionCable
+  module Connection
+    class StreamEventLoop
+      def initialize
+        @nio = @executor = @thread = nil
+        @map = {}
+        @stopping = false
+        @todo = Queue.new
+
+        @spawn_mutex = Mutex.new
+      end
+
+      def timer(interval, &block)
+        Concurrent::TimerTask.new(execution_interval: interval, &block).tap(&:execute)
+      end
+
+      def post(task = nil, &block)
+        task ||= block
+
+        spawn
+        @executor << task
+      end
+
+      def attach(io, stream)
+        @todo << lambda do
+          @map[io] = @nio.register(io, :r)
+          @map[io].value = stream
+        end
+        wakeup
+      end
+
+      def detach(io, stream)
+        @todo << lambda do
+          @nio.deregister io
+          @map.delete io
+          io.close
+        end
+        wakeup
+      end
+
+      def writes_pending(io)
+        @todo << lambda do
+          if monitor = @map[io]
+            monitor.interests = :rw
+          end
+        end
+        wakeup
+      end
+
+      def stop
+        @stopping = true
+        wakeup if @nio
+      end
+
+      private
+        def spawn
+          return if @thread && @thread.status
+
+          @spawn_mutex.synchronize do
+            return if @thread && @thread.status
+
+            @nio ||= NIO::Selector.new
+
+            @executor ||= Concurrent::ThreadPoolExecutor.new(
+              min_threads: 1,
+              max_threads: 10,
+              max_queue: 0,
+            )
+
+            @thread = Thread.new { run }
+
+            return true
+          end
+        end
+
+        def wakeup
+          spawn || @nio.wakeup
+        end
+
+        def run
+          loop do
+            if @stopping
+              @nio.close
+              break
+            end
+
+            until @todo.empty?
+              @todo.pop(true).call
+            end
+
+            next unless monitors = @nio.select
+
+            monitors.each do |monitor|
+              io = monitor.io
+              stream = monitor.value
+
+              begin
+                if monitor.writable?
+                  if stream.flush_write_buffer
+                    monitor.interests = :r
+                  end
+                  next unless monitor.readable?
+                end
+
+                incoming = io.read_nonblock(4096, exception: false)
+                case incoming
+                when :wait_readable
+                  next
+                when nil
+                  stream.close
+                else
+                  stream.receive incoming
+                end
+              rescue
+                # We expect one of EOFError or Errno::ECONNRESET in
+                # normal operation (when the client goes away). But if
+                # anything else goes wrong, this is still the best way
+                # to handle it.
+                begin
+                  stream.close
+                rescue
+                  @nio.deregister io
+                  @map.delete io
+                end
+              end
+            end
+          end
+        end
+    end
+  end
+end