From 3fdcfef172ae3d2d73da0f3717deea7887164da6 Mon Sep 17 00:00:00 2001
From: st0012 <stan001212@gmail.com>
Date: Thu, 21 Jul 2022 22:30:27 +0100
Subject: [PATCH] Avoid setting @tc in thread_begin event

This event will be triggered before the new thread even has a
ThreadClient. So in this case, the @tc will be overridden to just nil,
which is wrong.

However, we also don't want to just set @tc to the new thread's
newly created ThreadClient. This is because a thread's creation can
happen during a subsession, and promptly switching @tc to another
thread's ThreadClient will misfire thread suspension.
---
 lib/debug/session.rb        | 14 ++++++++++----
 test/console/thread_test.rb | 24 ++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)
 create mode 100644 test/console/thread_test.rb

diff --git a/lib/debug/session.rb b/lib/debug/session.rb
index db287356c..303f3336d 100644
--- a/lib/debug/session.rb
+++ b/lib/debug/session.rb
@@ -213,18 +213,24 @@ def request_tc(req)
 
     def process_event evt
       # variable `@internal_info` is only used for test
-      @tc, output, ev, @internal_info, *ev_args = evt
+      tc, output, ev, @internal_info, *ev_args = evt
 
       output.each{|str| @ui.puts str} if ev != :suspend
 
-      case ev
-
-      when :thread_begin # special event, tc is nil
+      # special event, tc is nil
+      # and we don't want to set @tc to the newly created thread's ThreadClient
+      if ev == :thread_begin
         th = ev_args.shift
         q = ev_args.shift
         on_thread_begin th
         q << true
 
+        return
+      end
+
+      @tc = tc
+
+      case ev
       when :init
         enter_subsession
         wait_command_loop
diff --git a/test/console/thread_test.rb b/test/console/thread_test.rb
new file mode 100644
index 000000000..7ebb4bd31
--- /dev/null
+++ b/test/console/thread_test.rb
@@ -0,0 +1,24 @@
+require_relative '../support/console_test_case'
+
+module DEBUGGER__
+  class ThreadControlTest < ConsoleTestCase
+    def program
+      <<~RUBY
+       1| def foo
+       2|   Thread.new { sleep 5 }
+       3| end
+       4|
+       5| 5.times do
+       6|   foo
+       7|   binding.b(do: "1 == 2") # eval Ruby code in debugger
+       8| end
+      RUBY
+    end
+
+    def test_debugger_isnt_hung_by_new_threads
+      debug_code(program) do
+        type "c"
+      end
+    end
+  end
+end