refactor(stats): re-implement RotatingScope with thread local storage

Author: 王健

source/extensions/filters/http/istio_stats/istio_stats.cc

@@ -20,6 +20,7 @@
 #include "envoy/registry/registry.h"
 #include "envoy/server/factory_context.h"
 #include "envoy/singleton/manager.h"
+#include "envoy/thread_local/thread_local.h"
 #include "extensions/common/metadata_object.h"
 #include "parser/parser.h"
 #include "source/common/grpc/common.h"
@@ -313,7 +314,7 @@ struct Context : public Singleton::Instance {
 
 using ContextSharedPtr = std::shared_ptr<Context>;
 
-SINGLETON_MANAGER_REGISTRATION(Context)
+SINGLETON_MANAGER_REGISTRATION(istio_stats_filter_context)
 
 using google::api::expr::runtime::CelValue;
 
@@ -418,21 +419,21 @@ struct MetricOverrides : public Logger::Loggable<Logger::Id::filter> {
 // periodically to replace the current scope.
 //
 // The replaced stats scope is deleted gracefully after a minimum of 1s delay
-// for two reasons:
-//
-// 1. Stats flushing is asynchronous and the data may be lost if not flushed
-// before the deletion (see stats_flush_interval).
-//
-// 2. The implementation avoids locking by releasing a raw pointer to workers.
-// When the rotation happens on the main, the raw pointer may still be in-use
-// by workers for a short duration.
+// because of stats flushing is asynchronous and the data may be lost if not
+// flushed before the deletion (see stats_flush_interval).
 class RotatingScope : public Logger::Loggable<Logger::Id::filter> {
 public:
   RotatingScope(Server::Configuration::FactoryContext& factory_context, uint64_t rotate_interval_ms,
                 uint64_t delete_interval_ms)
       : parent_scope_(factory_context.scope()), active_scope_(parent_scope_.createScope("")),
-        raw_scope_(active_scope_.get()), rotate_interval_ms_(rotate_interval_ms),
+        tls_scope_(factory_context.serverFactoryContext().threadLocal()),
+        rotate_interval_ms_(rotate_interval_ms),
         delete_interval_ms_(delete_interval_ms) {
+
+    tls_scope_.set([&scope = *active_scope_](Event::Dispatcher&){
+        return std::make_shared<TlsCachedScope>(scope);
+    });
+
     if (rotate_interval_ms_ > 0) {
       ASSERT(delete_interval_ms_ < rotate_interval_ms_);
       ASSERT(delete_interval_ms_ >= 1000);
@@ -452,36 +453,58 @@ class RotatingScope : public Logger::Loggable<Logger::Id::filter> {
       delete_timer_.reset();
     }
   }
-  Stats::Scope* scope() { return raw_scope_.load(); }
+  Stats::Scope& scope() { return tls_scope_->_scope; }
 
 private:
+  struct TlsCachedScope:ThreadLocal::ThreadLocalObject{
+    TlsCachedScope(Stats::Scope& scope):_scope(scope) {};
+    std::reference_wrapper<Stats::Scope> _scope;
+  };
+
   void onRotate() {
     ENVOY_LOG(info, "Rotating active Istio stats scope after {}ms.", rotate_interval_ms_);
     draining_scope_ = active_scope_;
-    delete_timer_->enableTimer(std::chrono::milliseconds(delete_interval_ms_));
     active_scope_ = parent_scope_.createScope("");
-    raw_scope_.store(active_scope_.get());
-    rotate_timer_->enableTimer(std::chrono::milliseconds(rotate_interval_ms_));
+    tls_scope_.runOnAllThreads(
+        [&scope = *active_scope_](OptRef<TlsCachedScope> tls_cache) {
+            tls_cache->_scope = scope;
+         },
+         // Start the delete and rotate timer after the new scope has been propagated to all worker threads.
+         // The RotatingScope instance can go away before the dispatcher has a chance to execute the callback
+         // and the still_alive shared_ptr will be deallocated when the current instance is deallocated.
+         // We rely on a weak_ptr to still_alive flag to determine if the instance is still valid.
+        [this, maybe_still_alive = std::weak_ptr<bool>(still_alive_)]() -> void {
+          if(!maybe_still_alive.expired()){
+            delete_timer_->enableTimer(std::chrono::milliseconds(delete_interval_ms_));
+            rotate_timer_->enableTimer(std::chrono::milliseconds(rotate_interval_ms_));
+          }
+        });
   }
   void onDelete() {
     ENVOY_LOG(info, "Deleting draining Istio stats scope after {}ms.", delete_interval_ms_);
     draining_scope_.reset();
   }
+
   Stats::Scope& parent_scope_;
   Stats::ScopeSharedPtr active_scope_;
-  std::atomic<Stats::Scope*> raw_scope_;
   Stats::ScopeSharedPtr draining_scope_{nullptr};
+  ThreadLocal::TypedSlot<TlsCachedScope> tls_scope_;
   const uint64_t rotate_interval_ms_;
   const uint64_t delete_interval_ms_;
   Event::TimerPtr rotate_timer_{nullptr};
   Event::TimerPtr delete_timer_{nullptr};
+
+  // A sentinel shared_ptr used for keeping track of whether the RotatingContext is still alive.
+  // It is only held by a weak reference in the callback that will be invoked after the new active
+  // scope has been propagated to all worker threads.
+  std::shared_ptr<bool> still_alive_{std::make_shared<bool>(true)};
 };
 
 struct Config : public Logger::Loggable<Logger::Id::filter> {
   Config(const stats::PluginConfig& proto_config,
          Server::Configuration::FactoryContext& factory_context)
       : context_(factory_context.serverFactoryContext().singletonManager().getTyped<Context>(
-            SINGLETON_MANAGER_REGISTERED_NAME(Context),
+            SINGLETON_MANAGER_REGISTERED_NAME(istio_stats_filter_context),
             [&factory_context] {
               return std::make_shared<Context>(
                   factory_context.serverFactoryContext().scope().symbolTable(),
@@ -514,7 +537,7 @@ struct Config : public Logger::Loggable<Logger::Id::filter> {
       break;
     }
     if (proto_config.metrics_size() > 0 || proto_config.definitions_size() > 0) {
-      metric_overrides_ = std::make_unique<MetricOverrides>(context_, scope()->symbolTable());
+      metric_overrides_ = std::make_unique<MetricOverrides>(context_, scope().symbolTable());
       for (const auto& definition : proto_config.definitions()) {
         const auto& it = context_->all_metrics_.find(definition.name());
         if (it != context_->all_metrics_.end()) {
@@ -698,12 +721,12 @@ struct Config : public Logger::Loggable<Logger::Id::filter> {
           return;
         }
         auto new_tags = parent_.metric_overrides_->overrideTags(metric, tags, expr_values_);
-        Stats::Utility::counterFromStatNames(*parent_.scope(),
+        Stats::Utility::counterFromStatNames(parent_.scope(),
                                              {parent_.context_->stat_namespace_, metric}, new_tags)
             .add(amount);
         return;
       }
-      Stats::Utility::counterFromStatNames(*parent_.scope(),
+      Stats::Utility::counterFromStatNames(parent_.scope(),
                                            {parent_.context_->stat_namespace_, metric}, tags)
           .add(amount);
     }
@@ -717,12 +740,12 @@ struct Config : public Logger::Loggable<Logger::Id::filter> {
         }
         auto new_tags = parent_.metric_overrides_->overrideTags(metric, tags, expr_values_);
         Stats::Utility::histogramFromStatNames(
-            *parent_.scope(), {parent_.context_->stat_namespace_, metric}, unit, new_tags)
+            parent_.scope(), {parent_.context_->stat_namespace_, metric}, unit, new_tags)
             .recordValue(value);
         return;
       }
       Stats::Utility::histogramFromStatNames(
-          *parent_.scope(), {parent_.context_->stat_namespace_, metric}, unit, tags)
+          parent_.scope(), {parent_.context_->stat_namespace_, metric}, unit, tags)
           .recordValue(value);
     }
 
@@ -735,17 +758,17 @@ struct Config : public Logger::Loggable<Logger::Id::filter> {
           switch (metric.type_) {
           case MetricOverrides::MetricType::Counter:
             Stats::Utility::counterFromStatNames(
-                *parent_.scope(), {parent_.context_->stat_namespace_, metric.name_}, tags)
+                parent_.scope(), {parent_.context_->stat_namespace_, metric.name_}, tags)
                 .add(amount);
             break;
           case MetricOverrides::MetricType::Histogram:
             Stats::Utility::histogramFromStatNames(
-                *parent_.scope(), {parent_.context_->stat_namespace_, metric.name_},
+                parent_.scope(), {parent_.context_->stat_namespace_, metric.name_},
                 Stats::Histogram::Unit::Bytes, tags)
                 .recordValue(amount);
             break;
           case MetricOverrides::MetricType::Gauge:
-            Stats::Utility::gaugeFromStatNames(*parent_.scope(),
+            Stats::Utility::gaugeFromStatNames(parent_.scope(),
                                                {parent_.context_->stat_namespace_, metric.name_},
                                                Stats::Gauge::ImportMode::Accumulate, tags)
                 .set(amount);
@@ -769,14 +792,14 @@ struct Config : public Logger::Loggable<Logger::Id::filter> {
     tags.push_back({context_->tag_, context_->istio_version_.empty() ? context_->unknown_
                                                                      : context_->istio_version_});
 
-    Stats::Utility::gaugeFromStatNames(*scope(),
+    Stats::Utility::gaugeFromStatNames(scope(),
                                        {context_->stat_namespace_, context_->istio_build_},
                                        Stats::Gauge::ImportMode::Accumulate, tags)
         .set(1);
   }
 
   Reporter reporter() const { return reporter_; }
-  Stats::Scope* scope() { return scope_.scope(); }
+  Stats::Scope& scope() { return scope_.scope(); }
 
   ContextSharedPtr context_;
   RotatingScope scope_;
@@ -795,7 +818,7 @@ class IstioStatsFilter : public Http::PassThroughFilter,
                          public Network::ConnectionCallbacks {
 public:
   IstioStatsFilter(ConfigSharedPtr config)
-      : config_(config), context_(*config->context_), pool_(config->scope()->symbolTable()),
+      : config_(config), context_(*config->context_), pool_(config->scope().symbolTable()),
         stream_(*config_, pool_) {
     tags_.reserve(25);
     switch (config_->reporter()) {