Add Ractor#monitor and Ractor#unmonitor

Author: soutaro

core/ractor.rbs

@@ -453,6 +453,25 @@ class Ractor
   #
   def name: () -> String?
 
+  # <!--
+  #   rdoc-file=ractor.rb
+  #   - ractor.monitor(port) -> self
+  # -->
+  # Register port as a monitoring port. If the ractor terminated, the port
+  # received a Symbol object. :exited will be sent if the ractor terminated
+  # without an exception. :aborted will be sent if the ractor terminated with a
+  # exception.
+  #
+  #     r = Ractor.new{ some_task() }
+  #     r.monitor(port = Ractor::Port.new)
+  #     port.receive #=> :exited and r is terminated
+  #
+  #     r = Ractor.new{ raise "foo" }
+  #     r.monitor(port = Ractor::Port.new)
+  #     port.receive #=> :terminated and r is terminated with an exception "foo"
+  #
+  def monitor: [T < Symbol] (Port[T]) -> untyped
+
   # <!--
   #   rdoc-file=ractor.rb
   #   - ractor.send(msg) -> self
@@ -468,6 +487,14 @@ class Ractor
   #
   alias to_s inspect
 
+  # <!--
+  #   rdoc-file=ractor.rb
+  #   - ractor.unmonitor(port) -> self
+  # -->
+  # Unregister port from the monitoring ports.
+  #
+  def unmonitor: (Port[untyped]) -> self
+
   # <!--
   #   rdoc-file=ractor.rb
   #   - ractor.value -> obj

test/stdlib/Ractor_test.rb

@@ -116,6 +116,15 @@ def test_name
                      named, :name
   end
 
+  def test_monitor
+    ractor = Ractor.new { sleep(0.1) }
+
+    assert_send_type(
+      "(::Ractor::Port[untyped]) -> untyped",
+      ractor, :monitor, Ractor::Port.new
+    )
+  end
+
   def test_send
     r = Ractor.new { sleep }
 
@@ -132,6 +141,19 @@ def test_to_s
                      Ractor.current, :to_s
   end
 
+  def test_unmonitor
+    ractor = Ractor.new { sleep(0.1) }
+
+    port = Ractor::Port.new
+
+    ractor.monitor(port)
+
+    assert_send_type(
+      "(::Ractor::Port[untyped]) -> ::Ractor",
+      ractor, :unmonitor, port
+    )
+  end
+
   def test_value
     ractor = Ractor.new { 123 }