upstream: avoid quadratic time complexity in server initialization (#15237)

Currently ClusterManagerInitHelper.secondary_init_clusters_ is a list.
Upon every insert the list gets searched for an already added cluster
with the same name. Since in normal circumstances all new clusters
have unique names the worst case scenario is triggered and all elements
of the list are checked sequentially upon every cluster added.

Replace the list with a hash map.

Signed-off-by: Dmitry Rozhkov <dmitry.rozhkov@intel.com>

Author: rojkov

source/common/upstream/cluster_manager_impl.cc

@@ -3,7 +3,6 @@
 #include <chrono>
 #include <cstdint>
 #include <functional>
-#include <list>
 #include <memory>
 #include <string>
 #include <vector>
@@ -66,20 +65,12 @@ void ClusterManagerInitHelper::addCluster(ClusterManagerCluster& cm_cluster) {
   Cluster& cluster = cm_cluster.cluster();
   if (cluster.initializePhase() == Cluster::InitializePhase::Primary) {
     // Remove the previous cluster before the cluster object is destroyed.
-    primary_init_clusters_.remove_if(
-        [name_to_remove = cluster.info()->name()](ClusterManagerCluster* cluster_iter) {
-          return cluster_iter->cluster().info()->name() == name_to_remove;
-        });
-    primary_init_clusters_.push_back(&cm_cluster);
+    primary_init_clusters_.insert_or_assign(cm_cluster.cluster().info()->name(), &cm_cluster);
     cluster.initialize(initialize_cb);
   } else {
     ASSERT(cluster.initializePhase() == Cluster::InitializePhase::Secondary);
     // Remove the previous cluster before the cluster object is destroyed.
-    secondary_init_clusters_.remove_if(
-        [name_to_remove = cluster.info()->name()](ClusterManagerCluster* cluster_iter) {
-          return cluster_iter->cluster().info()->name() == name_to_remove;
-        });
-    secondary_init_clusters_.push_back(&cm_cluster);
+    secondary_init_clusters_.insert_or_assign(cm_cluster.cluster().info()->name(), &cm_cluster);
     if (started_secondary_initialize_) {
       // This can happen if we get a second CDS update that adds new clusters after we have
       // already started secondary init. In this case, just immediately initialize.
@@ -104,17 +95,20 @@ void ClusterManagerInitHelper::removeCluster(ClusterManagerCluster& cluster) {
 
   // There is a remote edge case where we can remove a cluster via CDS that has not yet been
   // initialized. When called via the remove cluster API this code catches that case.
-  std::list<ClusterManagerCluster*>* cluster_list;
+  absl::flat_hash_map<std::string, ClusterManagerCluster*>* cluster_map;
   if (cluster.cluster().initializePhase() == Cluster::InitializePhase::Primary) {
-    cluster_list = &primary_init_clusters_;
+    cluster_map = &primary_init_clusters_;
   } else {
     ASSERT(cluster.cluster().initializePhase() == Cluster::InitializePhase::Secondary);
-    cluster_list = &secondary_init_clusters_;
+    cluster_map = &secondary_init_clusters_;
   }
 
   // It is possible that the cluster we are removing has already been initialized, and is not
-  // present in the initializer list. If so, this is fine.
-  cluster_list->remove(&cluster);
+  // present in the initializer map. If so, this is fine.
+  absl::string_view cluster_name = cluster.cluster().info()->name();
+  if (cluster_map->at(cluster_name) == &cluster) {
+    cluster_map->erase(cluster_name);
+  }
   ENVOY_LOG(debug, "cm init: init complete: cluster={} primary={} secondary={}",
             cluster.cluster().info()->name(), primary_init_clusters_.size(),
             secondary_init_clusters_.size());
@@ -123,13 +117,13 @@ void ClusterManagerInitHelper::removeCluster(ClusterManagerCluster& cluster) {
 
 void ClusterManagerInitHelper::initializeSecondaryClusters() {
   started_secondary_initialize_ = true;
-  // Cluster::initialize() method can modify the list of secondary_init_clusters_ to remove
+  // Cluster::initialize() method can modify the map of secondary_init_clusters_ to remove
   // the item currently being initialized, so we eschew range-based-for and do this complicated
   // dance to increment the iterator before calling initialize.
   for (auto iter = secondary_init_clusters_.begin(); iter != secondary_init_clusters_.end();) {
-    ClusterManagerCluster* cluster = *iter;
+    ClusterManagerCluster* cluster = iter->second;
+    ENVOY_LOG(debug, "initializing secondary cluster {}", iter->first);
     ++iter;
-    ENVOY_LOG(debug, "initializing secondary cluster {}", cluster->cluster().info()->name());
     cluster->cluster().initialize([cluster, this] { onClusterInit(*cluster); });
   }
 }

source/common/upstream/cluster_manager_impl.h

@@ -188,8 +188,8 @@ class ClusterManagerInitHelper : Logger::Loggable<Logger::Id::upstream> {
   CdsApi* cds_{};
   ClusterManager::PrimaryClustersReadyCallback primary_clusters_initialized_callback_;
   ClusterManager::InitializationCompleteCallback initialized_callback_;
-  std::list<ClusterManagerCluster*> primary_init_clusters_;
-  std::list<ClusterManagerCluster*> secondary_init_clusters_;
+  absl::flat_hash_map<std::string, ClusterManagerCluster*> primary_init_clusters_;
+  absl::flat_hash_map<std::string, ClusterManagerCluster*> secondary_init_clusters_;
   State state_{State::Loading};
   bool started_secondary_initialize_{};
 };