Remove subchannel pool from global init (#28987)

* Remove subchannel pool from global init

This can be initialized independently, so let's do so.

* fix

* fix

* cleanup

src/core/ext/filters/client_channel/client_channel_plugin.cc

@@ -42,12 +42,10 @@ void grpc_client_channel_init(void) {
   grpc_core::LoadBalancingPolicyRegistry::Builder::InitRegistry();
   grpc_core::ProxyMapperRegistry::Init();
   grpc_core::RegisterHttpProxyMapper();
-  grpc_core::GlobalSubchannelPool::Init();
   grpc_client_channel_global_init_backup_polling();
 }
 
 void grpc_client_channel_shutdown(void) {
-  grpc_core::GlobalSubchannelPool::Shutdown();
   grpc_core::ProxyMapperRegistry::Shutdown();
   grpc_core::LoadBalancingPolicyRegistry::Builder::ShutdownRegistry();
 }

src/core/ext/filters/client_channel/global_subchannel_pool.cc

@@ -24,27 +24,9 @@
 
 namespace grpc_core {
 
-#define GRPC_REGISTER_SUBCHANNEL_CALM_DOWN_AFTER_ATTEMPTS 100
-#define GRPC_REGISTER_SUBCHANNEL_CALM_DOWN_MICROS 10
-
-void GlobalSubchannelPool::Init() {
-  instance_ = new RefCountedPtr<GlobalSubchannelPool>(
-      MakeRefCounted<GlobalSubchannelPool>());
-}
-
-void GlobalSubchannelPool::Shutdown() {
-  // To ensure Init() was called before.
-  GPR_ASSERT(instance_ != nullptr);
-  // To ensure Shutdown() was not called before.
-  GPR_ASSERT(*instance_ != nullptr);
-  instance_->reset();
-  delete instance_;
-}
-
 RefCountedPtr<GlobalSubchannelPool> GlobalSubchannelPool::instance() {
-  GPR_ASSERT(instance_ != nullptr);
-  GPR_ASSERT(*instance_ != nullptr);
-  return *instance_;
+  static GlobalSubchannelPool* p = new GlobalSubchannelPool();
+  return p->Ref();
 }
 
 RefCountedPtr<Subchannel> GlobalSubchannelPool::RegisterSubchannel(
@@ -59,8 +41,6 @@ RefCountedPtr<Subchannel> GlobalSubchannelPool::RegisterSubchannel(
   return constructed;
 }
 
-RefCountedPtr<GlobalSubchannelPool>* GlobalSubchannelPool::instance_ = nullptr;
-
 void GlobalSubchannelPool::UnregisterSubchannel(const SubchannelKey& key,
                                                 Subchannel* subchannel) {
   MutexLock lock(&mu_);

src/core/ext/filters/client_channel/global_subchannel_pool.h

@@ -29,20 +29,9 @@
 namespace grpc_core {
 
 // The global subchannel pool. It shares subchannels among channels. There
-// should be only one instance of this class. Init() should be called once at
-// the filter initialization time; Shutdown() should be called once at the
-// filter shutdown time.
+// should be only one instance of this class.
 class GlobalSubchannelPool final : public SubchannelPoolInterface {
  public:
-  // The ctor and dtor are not intended to use directly.
-  GlobalSubchannelPool() {}
-  ~GlobalSubchannelPool() override {}
-
-  // Should be called exactly once at filter initialization time.
-  static void Init();
-  // Should be called exactly once at filter shutdown time.
-  static void Shutdown();
-
   // Gets the singleton instance.
   static RefCountedPtr<GlobalSubchannelPool> instance();
 
@@ -57,9 +46,8 @@ class GlobalSubchannelPool final : public SubchannelPoolInterface {
       ABSL_LOCKS_EXCLUDED(mu_);
 
  private:
-  // The singleton instance. (It's a pointer to RefCountedPtr so that this
-  // non-local static object can be trivially destructible.)
-  static RefCountedPtr<GlobalSubchannelPool>* instance_;
+  GlobalSubchannelPool() {}
+  ~GlobalSubchannelPool() override {}
 
   // A map from subchannel key to subchannel.
   std::map<SubchannelKey, Subchannel*> subchannel_map_ ABSL_GUARDED_BY(mu_);