pull global tracer list from TraceFlag class

src/core/lib/debug/trace.cc

@@ -29,17 +29,19 @@ int grpc_tracer_set_enabled(const char* name, int enabled);
 
 namespace grpc_core {
 
-TraceFlag* TraceFlag::root_tracer_ = nullptr;
+// there is only ever one global list of tracers for the entire program.
+static TraceFlag* g_root_tracer = nullptr;
 
+// Flags register themselves on the list during construction
 TraceFlag::TraceFlag(bool default_enabled, const char* name)
-    : next_tracer_(root_tracer_), name_(name), value_(default_enabled) {
+    : next_tracer_(g_root_tracer), name_(name), value_(default_enabled) {
-  root_tracer_ = this;
+  g_root_tracer = this;
 }
 
 void TraceFlag::LogAllTracers() {
   gpr_log(GPR_DEBUG, "available tracers:");
   TraceFlag* t;
-  for (t = root_tracer_; t != nullptr; t = t->next_tracer_) {
+  for (t = g_root_tracer; t != nullptr; t = t->next_tracer_) {
     gpr_log(GPR_DEBUG, "\t%s", t->name_);
   }
 }
@@ -47,20 +49,20 @@ void TraceFlag::LogAllTracers() {
 bool TraceFlag::Set(const char* name, bool enabled) {
   TraceFlag* t;
   if (0 == strcmp(name, "all")) {
-    for (t = root_tracer_; t; t = t->next_tracer_) {
+    for (t = g_root_tracer; t; t = t->next_tracer_) {
       t->set_enabled(enabled);
     }
   } else if (0 == strcmp(name, "list_tracers")) {
     LogAllTracers();
   } else if (0 == strcmp(name, "refcount")) {
-    for (t = root_tracer_; t; t = t->next_tracer_) {
+    for (t = g_root_tracer; t; t = t->next_tracer_) {
       if (strstr(t->name_, "refcount") != nullptr) {
         t->set_enabled(enabled);
       }
     }
   } else {
     bool found = false;
-    for (t = root_tracer_; t; t = t->next_tracer_) {
+    for (t = g_root_tracer; t; t = t->next_tracer_) {
       if (0 == strcmp(name, t->name_)) {
         t->set_enabled(enabled);
         found = true;

src/core/lib/debug/trace.h

@@ -46,15 +46,16 @@ namespace grpc_core {
 
 class TraceFlag {
   friend class TraceFlagPeer;
+  friend class TracerList;
 
  public:
   TraceFlag(bool default_enabled, const char* name);
   ~TraceFlag() {}
 
-  static bool Set(const char* tracer, bool enabled);
-
   const char* name() const { return name_; }
 
+  static bool Set(const char* name, bool enabled);
+
   bool enabled() {
 #ifdef GRPC_THREADSAFE_TRACER
     return gpr_atm_no_barrier_load(&value_) != 0;
@@ -74,7 +75,6 @@ class TraceFlag {
 #endif
   }
 
-  static TraceFlag* root_tracer_;
   TraceFlag* next_tracer_;
   const char* const name_;
 #ifdef GRPC_THREADSAFE_TRACER