From a991cfd6bdc4f1666ea321be132899aae3c9b8e0 Mon Sep 17 00:00:00 2001
From: Walt Karas <wkaras@yahooinc.com>
Date: Tue, 5 Sep 2023 23:37:49 +0000
Subject: [PATCH] Allow DbgCtl tag to be set after instance construction.

---
 include/ts/DbgCtl.h  | 34 ++++++++++++++++++++++++++++------
 src/tscore/DbgCtl.cc | 20 ++++++++++++++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/include/ts/DbgCtl.h b/include/ts/DbgCtl.h
index 1bd08988e9f..1aac8644614 100644
--- a/include/ts/DbgCtl.h
+++ b/include/ts/DbgCtl.h
@@ -38,7 +38,31 @@ class DbgCtl
   //
   DbgCtl(char const *tag) : _ptr{_new_reference(tag)} {}
 
-  ~DbgCtl() { _rm_reference(); }
+  // As instance with no tag will always be off.
+  //
+  DbgCtl() : _ptr{&_No_tag_dummy} {}
+
+  ~DbgCtl()
+  {
+    if (_ptr != &_No_tag_dummy) {
+      _rm_reference();
+    }
+  }
+
+  // No copying. Only moving from a tagged to a tagless instance allowed.
+  //
+  DbgCtl(DbgCtl const &)            = delete;
+  DbgCtl &operator=(DbgCtl const &) = delete;
+  DbgCtl(DbgCtl &&);
+  DbgCtl &operator=(DbgCtl &&);
+
+  // A shorthand.
+  //
+  void
+  set(char const *tag)
+  {
+    *this = DbgCtl{tag};
+  }
 
   bool
   tag_on() const
@@ -90,14 +114,12 @@ class DbgCtl
   static void print(char const *tag, char const *file, char const *function, int line, char const *fmt_str, ...)
     TS_PRINTFLIKE(5, 6);
 
-  // No copying/moving.
-  DbgCtl(DbgCtl const &)            = delete;
-  DbgCtl &operator=(DbgCtl const &) = delete;
-
 private:
   using _TagData = std::pair<char const *const, bool>;
 
-  _TagData const *const _ptr;
+  _TagData const *_ptr;
+
+  static const _TagData _No_tag_dummy;
 
   static const _TagData *_new_reference(char const *tag);
 
diff --git a/src/tscore/DbgCtl.cc b/src/tscore/DbgCtl.cc
index 8ae652eb20b..0c5cad85fd6 100644
--- a/src/tscore/DbgCtl.cc
+++ b/src/tscore/DbgCtl.cc
@@ -30,6 +30,24 @@
 #include <tscore/ink_assert.h>
 #include <tscore/Diags.h>
 
+DbgCtl::DbgCtl(DbgCtl &&src)
+{
+  ink_release_assert(src._ptr != &_No_tag_dummy);
+
+  _ptr     = src._ptr;
+  src._ptr = &_No_tag_dummy;
+}
+
+DbgCtl &
+DbgCtl::operator=(DbgCtl &&src)
+{
+  ink_release_assert(&_No_tag_dummy == _ptr);
+
+  new (this) DbgCtl{std::move(src)};
+
+  return *this;
+}
+
 // The resistry of fast debug controllers has a ugly implementation to handle the whole-program initialization
 // and destruction order problem with C++.
 //
@@ -205,3 +223,5 @@ DbgCtl::_override_global_on()
 {
   return diags()->get_override();
 }
+
+DbgCtl::_TagData const DbgCtl::_No_tag_dummy{nullptr, false};