Rewrite channelz registry in terms of inlined vector

src/core/lib/channel/channelz_registry.cc

@@ -26,27 +26,14 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
+#include <cstring>
+
 namespace grpc_core {
 namespace {
 
 // singleton instance of the registry.
 ChannelzRegistry* g_channelz_registry = nullptr;
 
-// avl vtable for uuid (intptr_t) -> channelz_obj (void*)
-// this table is only looking, it does not own anything.
-void destroy_intptr(void* not_used, void* user_data) {}
-void* copy_intptr(void* key, void* user_data) { return key; }
-long compare_intptr(void* key1, void* key2, void* user_data) {
-  return GPR_ICMP(key1, key2);
-}
-
-void destroy_channelz_obj(void* channelz_obj, void* user_data) {}
-void* copy_channelz_obj(void* channelz_obj, void* user_data) {
-  return channelz_obj;
-}
-const grpc_avl_vtable avl_vtable = {destroy_intptr, copy_intptr, compare_intptr,
-                                    destroy_channelz_obj, copy_channelz_obj};
-
 }  // anonymous namespace
 
 void ChannelzRegistry::Init() { g_channelz_registry = New<ChannelzRegistry>(); }
@@ -58,19 +45,24 @@ ChannelzRegistry* ChannelzRegistry::Default() {
   return g_channelz_registry;
 }
 
-ChannelzRegistry::ChannelzRegistry() : uuid_(1) {
+ChannelzRegistry::ChannelzRegistry() {
   gpr_mu_init(&mu_);
-  avl_ = grpc_avl_create(&avl_vtable);
+  // init elements to nullptr
+  memset(entities_.data(), 0, sizeof(void*) * entities_.capacity());
 }
 
 ChannelzRegistry::~ChannelzRegistry() {
-  grpc_avl_unref(avl_, nullptr);
+  // null out all elements so that the destructors don't try to run.
+  // this is a "view only" object.
+  memset(entities_.data(), 0, sizeof(void*) * entities_.capacity());
   gpr_mu_destroy(&mu_);
 }
 
 void ChannelzRegistry::InternalUnregister(intptr_t uuid) {
+  GPR_ASSERT(uuid >= 1);
   gpr_mu_lock(&mu_);
-  avl_ = grpc_avl_remove(avl_, (void*)uuid, nullptr);
+  GPR_ASSERT((size_t)uuid <= entities_.size());
+  entities_[uuid - 1] = nullptr;
   gpr_mu_unlock(&mu_);
 }
 

src/core/lib/channel/channelz_registry.h

@@ -23,6 +23,7 @@
 
 #include "src/core/lib/avl/avl.h"
 #include "src/core/lib/channel/channel_trace.h"
+#include "src/core/lib/gprpp/inlined_vector.h"
 
 #include <stdint.h>
 
@@ -67,11 +68,11 @@ class ChannelzRegistry {
   // globally registers a channelz Object. Returns its unique uuid
   template <typename Object>
   intptr_t InternalRegister(Object* object) {
-    intptr_t prior = gpr_atm_no_barrier_fetch_add(&uuid_, 1);
     gpr_mu_lock(&mu_);
-    avl_ = grpc_avl_add(avl_, (void*)prior, object, nullptr);
+    entities_.push_back(static_cast<void*>(object));
+    intptr_t uuid = entities_.size();
     gpr_mu_unlock(&mu_);
-    return prior;
+    return uuid;
   }
 
   // globally unregisters the object that is associated to uuid.
@@ -82,16 +83,20 @@ class ChannelzRegistry {
   template <typename Object>
   Object* InternalGet(intptr_t uuid) {
     gpr_mu_lock(&mu_);
-    Object* ret =
-        static_cast<Object*>(grpc_avl_get(avl_, (void*)uuid, nullptr));
+    if (uuid < 1 || uuid > static_cast<intptr_t>(entities_.size())) {
+      gpr_mu_unlock(&mu_);
+      return nullptr;
+    }
+    Object* ret = static_cast<Object*>(entities_[uuid - 1]);
     gpr_mu_unlock(&mu_);
     return ret;
   }
 
   // private members
+
+  // protects entities_ and uuid_
   gpr_mu mu_;
-  grpc_avl avl_;
-  gpr_atm uuid_;
+  InlinedVector<void*, 20> entities_;
 };
 
 }  // namespace grpc_core

test/core/channel/channelz_registry_test.cc

@@ -82,6 +82,15 @@ TEST(ChannelzRegistryTest, MultipleTypeTest) {
   EXPECT_EQ(&str_to_register, retrieved_str);
 }
 
+TEST(ChannelzRegistryTest, RegisterManyItems) {
+  int object_to_register = 42;
+  for (int i = 0; i < 100; i++) {
+    intptr_t uuid = ChannelzRegistry::Register(&object_to_register);
+    int* retrieved = ChannelzRegistry::Get<int>(uuid);
+    EXPECT_EQ(&object_to_register, retrieved);
+  }
+}
+
 namespace {
 class Foo {
  public: