Restart threads on DAP evaluation

This makes sure DAP evaluation request also doesn't hang.

See ruby#947 for the original console implementation.

lib/debug/server_dap.rb

@@ -625,6 +625,7 @@ def process_protocol_request req
           expr = req.dig('arguments', 'expression')
 
           if find_waiting_tc(tid)
+            restart_all_threads
             request_tc [:dap, :evaluate, req, fid, expr, context]
           else
             fail_response req
@@ -701,6 +702,7 @@ def process_protocol_result args
         register_vars result[:variables], tid
         @ui.respond req, result
       when :evaluate
+        stop_all_threads
         message = result.delete :message
         if message
           @ui.respond req, success: false, message: message

test/protocol/eval_test.rb

@@ -57,4 +57,27 @@ def test_eval_evaluates_arithmetic_expressions
       end
     end
   end
+
+  class EvaluateThreadTest < ProtocolTestCase
+    PROGRAM = <<~RUBY
+      1| th0 = Thread.new{sleep}
+      2| m = Mutex.new; q = Queue.new
+      3| th1 = Thread.new do
+      4|   m.lock; q << true
+      5|   sleep 1
+      6|   m.unlock
+      7| end
+      8| q.pop # wait for locking
+      9| p :ok
+    RUBY
+
+    def test_eval_with_threads
+      run_protocol_scenario PROGRAM, cdp: false do
+        req_add_breakpoint 9
+        req_continue
+        assert_repl_result({value: 'false', type: 'FalseClass'}, 'm.lock.nil?', frame_idx: 0)
+        req_continue
+      end
+    end
+  end
 end