fix(timer): ensure channel is closed once timer fires

src/tasker/timer.cr

@@ -7,25 +7,39 @@ class Timer
 
   def start_timer : Nil
     Log.trace { "timer start called, id: #{self.object_id}" }
-    spawn(same_thread: true) do
-      Log.trace { "timer waiting for #{@sleep_for} seconds, id: #{self.object_id}" }
-      select
-      when @cancel.receive
-        Log.trace { "timer cancelled, id: #{self.object_id}" }
-      when timeout(@sleep_for.seconds)
-        Log.trace { "timer fired, id: #{self.object_id}" }
-        @cancelled = true
-        @callback.call
-      end
-    end
+    spawn(same_thread: true) { schedule_wait }
     Fiber.yield
   end
 
   def cancel : Nil
     return if @cancelled
     Log.trace { "timer cancel requested, id: #{self.object_id}" }
     @cancelled = true
-    @cancel.send(true)
-    Fiber.yield
+    begin
+      @cancel.send(true)
+    rescue
+    end
+  end
+
+  private def schedule_wait
+    Log.trace { "timer waiting for #{@sleep_for} seconds, id: #{self.object_id}" }
+
+    select
+    when @cancel.receive
+      Log.trace { "timer cancelled, id: #{self.object_id}" }
+    when timeout(@sleep_for.seconds)
+      if !@cancelled
+        Log.trace { "timer fired, id: #{self.object_id}" }
+        @cancelled = true
+        @callback.call
+      else
+        Log.trace { "timer fired but ignored as cancelled, id: #{self.object_id}" }
+      end
+    end
+  rescue error
+    Log.warn(exception: error) { "error in tasker scheduler" }
+  ensure
+    @cancelled = true
+    @cancel.close
   end
 end