[Bug #21127] Thread deadlock does not display backtraces (#12721)

Previously, Ruby displayed backtraces for each thread on deadlock. However, it has not been shown since Ruby 3.0.
It should display the backtrace for debugging.

Co-authored-by: Jeremy Evans <code@jeremyevans.net>

eval_intern.h

@@ -300,6 +300,8 @@ void rb_vm_set_progname(VALUE filename);
 VALUE rb_vm_cbase(void);
 
 /* vm_backtrace.c */
+#define RUBY_BACKTRACE_START 0
+#define RUBY_ALL_BACKTRACE_LINES -1
 VALUE rb_ec_backtrace_object(const rb_execution_context_t *ec);
 VALUE rb_ec_backtrace_str_ary(const rb_execution_context_t *ec, long lev, long n);
 VALUE rb_ec_backtrace_location_ary(const rb_execution_context_t *ec, long lev, long n, bool skip_internal);

test/ruby/test_thread.rb

@@ -1553,4 +1553,36 @@ q.pop
     assert_equal(true, t.pending_interrupt?(Exception))
     assert_equal(false, t.pending_interrupt?(ArgumentError))
   end
+
+  def test_deadlock_backtrace
+    bug21127 = '[ruby-core:120930] [Bug #21127]'
+
+    expected_stderr = [
+      /-:12:in 'Thread#join': No live threads left. Deadlock\? \(fatal\)\n/,
+      /2 threads, 2 sleeps current:\w+ main thread:\w+\n/,
+      /\* #<Thread:\w+ sleep_forever>\n/,
+      :*,
+      /^\s*-:6:in 'Object#frame_for_deadlock_test_2'/,
+      :*,
+      /\* #<Thread:\w+ -:10 sleep_forever>\n/,
+      :*,
+      /^\s*-:2:in 'Object#frame_for_deadlock_test_1'/,
+      :*,
+    ]
+
+    assert_in_out_err([], <<-INPUT, [], expected_stderr, bug21127)
+      def frame_for_deadlock_test_1
+        yield
+      end
+
+      def frame_for_deadlock_test_2
+        yield
+      end
+
+      q = Thread::Queue.new
+      t = Thread.new { frame_for_deadlock_test_1 { q.pop } }
+
+      frame_for_deadlock_test_2 { t.join }
+    INPUT
+  end
 end

thread.c

@@ -5588,7 +5588,7 @@ debug_deadlock_check(rb_ractor_t *r, VALUE msg)
             }
         }
         rb_str_catf(msg, "\n   ");
-        rb_str_concat(msg, rb_ary_join(rb_ec_backtrace_str_ary(th->ec, 0, 0), sep));
+        rb_str_concat(msg, rb_ary_join(rb_ec_backtrace_str_ary(th->ec, RUBY_BACKTRACE_START, RUBY_ALL_BACKTRACE_LINES), sep));
         rb_str_catf(msg, "\n");
     }
 }

vm_backtrace.c

@@ -31,9 +31,6 @@ id2str(ID id)
 }
 #define rb_id2str(id) id2str(id)
 
-#define BACKTRACE_START 0
-#define ALL_BACKTRACE_LINES -1
-
 inline static int
 calc_pos(const rb_iseq_t *iseq, const VALUE *pc, int *lineno, int *node_id)
 {
@@ -758,7 +755,7 @@ rb_ec_partial_backtrace_object(const rb_execution_context_t *ec, long start_fram
 VALUE
 rb_ec_backtrace_object(const rb_execution_context_t *ec)
 {
-    return rb_ec_partial_backtrace_object(ec, BACKTRACE_START, ALL_BACKTRACE_LINES, NULL, FALSE, FALSE);
+    return rb_ec_partial_backtrace_object(ec, RUBY_BACKTRACE_START, RUBY_ALL_BACKTRACE_LINES, NULL, FALSE, FALSE);
 }
 
 static VALUE
@@ -1191,7 +1188,7 @@ rb_backtrace_each(VALUE (*iter)(VALUE recv, VALUE str), VALUE output)
 VALUE
 rb_make_backtrace(void)
 {
-    return rb_ec_backtrace_str_ary(GET_EC(), BACKTRACE_START, ALL_BACKTRACE_LINES);
+    return rb_ec_backtrace_str_ary(GET_EC(), RUBY_BACKTRACE_START, RUBY_ALL_BACKTRACE_LINES);
 }
 
 static long
@@ -1210,7 +1207,7 @@ ec_backtrace_range(const rb_execution_context_t *ec, int argc, const VALUE *argv
     switch (argc) {
       case 0:
         lev = lev_default + lev_plus;
-        n = ALL_BACKTRACE_LINES;
+        n = RUBY_ALL_BACKTRACE_LINES;
         break;
       case 1:
         {
@@ -1222,7 +1219,7 @@ ec_backtrace_range(const rb_execution_context_t *ec, int argc, const VALUE *argv
                     rb_raise(rb_eArgError, "negative level (%ld)", lev);
                 }
                 lev += lev_plus;
-                n = ALL_BACKTRACE_LINES;
+                n = RUBY_ALL_BACKTRACE_LINES;
                 break;
               case Qnil:
                 return -1;
@@ -1626,7 +1623,7 @@ rb_debug_inspector_open(rb_debug_inspector_func_t func, void *data)
 
     dbg_context.ec = ec;
     dbg_context.cfp = dbg_context.ec->cfp;
-    dbg_context.backtrace = rb_ec_backtrace_location_ary(ec, BACKTRACE_START, ALL_BACKTRACE_LINES, FALSE);
+    dbg_context.backtrace = rb_ec_backtrace_location_ary(ec, RUBY_BACKTRACE_START, RUBY_ALL_BACKTRACE_LINES, FALSE);
     dbg_context.backtrace_size = RARRAY_LEN(dbg_context.backtrace);
     dbg_context.contexts = collect_caller_bindings(ec);