[xDS] avoid creating duplicate hierarchical path attribute values (gr…

…pc#34106)

BUILD

@@ -1585,6 +1585,7 @@ grpc_cc_library(
         "//src/core:promise_status",
         "//src/core:race",
         "//src/core:ref_counted",
+        "//src/core:ref_counted_string",
         "//src/core:resolved_address",
         "//src/core:resource_quota",
         "//src/core:resource_quota_trace",

src/core/BUILD

@@ -960,6 +960,23 @@ grpc_cc_library(
     ],
 )
 
+grpc_cc_library(
+    name = "ref_counted_string",
+    srcs = [
+        "lib/gprpp/ref_counted_string.cc",
+    ],
+    hdrs = [
+        "lib/gprpp/ref_counted_string.h",
+    ],
+    external_deps = ["absl/strings"],
+    language = "c++",
+    deps = [
+        "ref_counted",
+        "//:gpr",
+        "//:ref_counted_ptr",
+    ],
+)
+
 grpc_cc_library(
     name = "uuid_v4",
     srcs = ["lib/gprpp/uuid_v4.cc"],
@@ -2680,6 +2697,7 @@ grpc_cc_library(
         "channel_stack_type",
         "dual_ref_counted",
         "ref_counted",
+        "ref_counted_string",
         "time",
         "useful",
         "//:channel_arg_names",
@@ -4499,6 +4517,7 @@ grpc_cc_library(
         "lb_policy_factory",
         "lb_policy_registry",
         "pollset_set",
+        "ref_counted_string",
         "validation_errors",
         "//:channel_arg_names",
         "//:config",
@@ -4653,6 +4672,7 @@ grpc_cc_library(
     deps = [
         "channel_args",
         "ref_counted",
+        "ref_counted_string",
         "//:gpr_platform",
         "//:ref_counted_ptr",
         "//:server_address",

src/core/ext/filters/client_channel/lb_policy/address_filtering.cc

@@ -36,7 +36,7 @@ int HierarchicalPathArg::ChannelArgsCompare(const HierarchicalPathArg* a,
                                             const HierarchicalPathArg* b) {
   for (size_t i = 0; i < a->path_.size(); ++i) {
     if (b->path_.size() == i) return 1;
-    int r = a->path_[i].compare(b->path_[i]);
+    int r = a->path_[i].as_string_view().compare(b->path_[i].as_string_view());
     if (r != 0) return r;
   }
   if (b->path_.size() > a->path_.size()) return -1;
@@ -47,19 +47,24 @@ absl::StatusOr<HierarchicalAddressMap> MakeHierarchicalAddressMap(
     const absl::StatusOr<ServerAddressList>& addresses) {
   if (!addresses.ok()) return addresses.status();
   HierarchicalAddressMap result;
+  RefCountedPtr<HierarchicalPathArg> remaining_path_attr;
   for (const ServerAddress& address : *addresses) {
     const auto* path_arg = address.args().GetObject<HierarchicalPathArg>();
     if (path_arg == nullptr) continue;
-    const std::vector<std::string>& path = path_arg->path();
+    const std::vector<RefCountedStringValue>& path = path_arg->path();
     auto it = path.begin();
     if (it == path.end()) continue;
     ServerAddressList& target_list = result[*it];
     ChannelArgs args = address.args();
     ++it;
     if (it != path.end()) {
-      std::vector<std::string> remaining_path(it, path.end());
-      args = args.SetObject(
-          MakeRefCounted<HierarchicalPathArg>(std::move(remaining_path)));
+      std::vector<RefCountedStringValue> remaining_path(it, path.end());
+      if (remaining_path_attr == nullptr ||
+          remaining_path_attr->path() != remaining_path) {
+        remaining_path_attr =
+            MakeRefCounted<HierarchicalPathArg>(std::move(remaining_path));
+      }
+      args = args.SetObject(remaining_path_attr);
     }
     target_list.emplace_back(address.address(), args);
   }

src/core/ext/filters/client_channel/lb_policy/address_filtering.h

@@ -20,14 +20,14 @@
 #include <grpc/support/port_platform.h>
 
 #include <map>
-#include <string>
 #include <utility>
 #include <vector>
 
 #include "absl/status/statusor.h"
 #include "absl/strings/string_view.h"
 
 #include "src/core/lib/gprpp/ref_counted.h"
+#include "src/core/lib/gprpp/ref_counted_string.h"
 #include "src/core/lib/resolver/server_address.h"
 
 // The resolver returns a flat list of addresses.  When a hierarchy of
@@ -88,23 +88,25 @@ namespace grpc_core {
 // to be associated with the address.
 class HierarchicalPathArg : public RefCounted<HierarchicalPathArg> {
  public:
-  explicit HierarchicalPathArg(std::vector<std::string> path)
+  explicit HierarchicalPathArg(std::vector<RefCountedStringValue> path)
       : path_(std::move(path)) {}
 
   // Channel arg traits methods.
   static absl::string_view ChannelArgName();
   static int ChannelArgsCompare(const HierarchicalPathArg* a,
                                 const HierarchicalPathArg* b);
 
-  const std::vector<std::string>& path() const { return path_; }
+  const std::vector<RefCountedStringValue>& path() const { return path_; }
 
  private:
-  std::vector<std::string> path_;
+  std::vector<RefCountedStringValue> path_;
 };
 
 // A map from the next path element to the addresses that fall under
 // that path element.
-using HierarchicalAddressMap = std::map<std::string, ServerAddressList>;
+using HierarchicalAddressMap =
+    std::map<RefCountedStringValue, ServerAddressList,
+             RefCountedStringValueLessThan>;
 
 // Splits up the addresses into a separate list for each child.
 absl::StatusOr<HierarchicalAddressMap> MakeHierarchicalAddressMap(

src/core/ext/filters/client_channel/lb_policy/priority/priority.cc

@@ -681,7 +681,12 @@ absl::Status PriorityLb::ChildPriority::UpdateLocked(
   UpdateArgs update_args;
   update_args.config = std::move(config);
   if (priority_policy_->addresses_.ok()) {
-    update_args.addresses = (*priority_policy_->addresses_)[name_];
+    auto it = priority_policy_->addresses_->find(name_);
+    if (it == priority_policy_->addresses_->end()) {
+      update_args.addresses.emplace();
+    } else {
+      update_args.addresses = it->second;
+    }
   } else {
     update_args.addresses = priority_policy_->addresses_.status();
   }