A workaround for ring hash on channel id to randomize the channel id (#28986)

* A workaround for ring hash on channel id to randomize the channel id
(ref to xds_resolver) used.

* using absl random functions.

BUILD

@@ -3568,6 +3568,7 @@ grpc_cc_library(
     external_deps = [
         "xxhash",
         "re2",
+        "absl/random",
         "absl/strings",
     ],
     language = "c++",

src/core/ext/filters/client_channel/resolver/xds/xds_resolver.cc

@@ -18,6 +18,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include "absl/random/random.h"
 #include "absl/strings/match.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/str_replace.h"
@@ -81,7 +82,8 @@ class XdsResolver : public Resolver {
         args_(grpc_channel_args_copy(args.args)),
         interested_parties_(args.pollset_set),
         uri_(std::move(args.uri)),
-        data_plane_authority_(GetDataPlaneAuthority(*args.args, uri_)) {
+        data_plane_authority_(GetDataPlaneAuthority(*args.args, uri_)),
+        channel_id_(absl::Uniform<uint64_t>(absl::BitGen())) {
     if (GRPC_TRACE_FLAG_ENABLED(grpc_xds_resolver_trace)) {
       gpr_log(
           GPR_INFO,
@@ -309,6 +311,7 @@ class XdsResolver : public Resolver {
   absl::StatusOr<RefCountedPtr<ServiceConfig>> CreateServiceConfig();
   void GenerateResult();
   void MaybeRemoveUnusedClusters();
+  uint64_t channel_id() const { return channel_id_; }
 
   std::shared_ptr<WorkSerializer> work_serializer_;
   std::unique_ptr<ResultHandler> result_handler_;
@@ -318,6 +321,7 @@ class XdsResolver : public Resolver {
   RefCountedPtr<XdsClient> xds_client_;
   std::string lds_resource_name_;
   std::string data_plane_authority_;
+  uint64_t channel_id_;
 
   ListenerWatcher* listener_watcher_ = nullptr;
   // This will not contain the RouteConfiguration, even if it comes with the
@@ -652,8 +656,7 @@ ConfigSelector::CallConfig XdsResolver::XdsConfigSelector::GetCallConfig(
         new_hash = HeaderHashHelper(hash_policy, args.initial_metadata);
         break;
       case XdsRouteConfigResource::Route::RouteAction::HashPolicy::CHANNEL_ID:
-        new_hash =
-            static_cast<uint64_t>(reinterpret_cast<uintptr_t>(resolver_.get()));
+        new_hash = resolver_->channel_id();
         break;
       default:
         GPR_ASSERT(0);
@@ -672,13 +675,7 @@ ConfigSelector::CallConfig XdsResolver::XdsConfigSelector::GetCallConfig(
     }
   }
   if (!hash.has_value()) {
-    // If there is no hash, we just choose a random value as a default.
-    // We cannot directly use the result of rand() as the hash value,
-    // since it is a 32-bit number and not a 64-bit number and will
-    // therefore not be evenly distributed.
-    uint32_t upper = rand();
-    uint32_t lower = rand();
-    hash = (static_cast<uint64_t>(upper) << 32) | lower;
+    hash = absl::Uniform<uint64_t>(absl::BitGen());
   }
   CallConfig call_config;
   if (method_config != nullptr) {