`rb_thread_t::serial` for debug

`rb_thread_t::serial` is auto-incremented serial number for
threads and it can overflow, it means the serial is not a ID
for each thread, it is only for debug print.

`RUBY_DEBUG_LOG` shows this information.

Also skip EC related information if EC is NULL. This patch
enable to use `RUBY_DEBUG_LOG` without setup EC.

1 files changed, 1 insertions, 0 deletions

diff --git a/vm_core.h b/vm_core.h
index f09dd8237e..f25b74dcdd 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -997,6 +997,7 @@ typedef struct rb_thread_struct {
     rb_execution_context_t *ec;
 
     struct rb_thread_sched_item sched;
+    rb_atomic_t serial; // only for RUBY_DEBUG_LOG()
 
     VALUE last_status; /* $? */