tls: Typesafe tls slots

include/envoy/thread_local/thread_local.h

@@ -89,6 +89,81 @@ class Slot {
 
 using SlotPtr = std::unique_ptr<Slot>;
 
+// Provides a typesafe API for slots.
+//
+// TODO(jmarantz): Rename the Slot class to something like RawSlot, where the
+// only reference is from TypedSlot, which we can then rename to Slot.
+template <class T> class TypedSlot {
+public:
+  /**
+   * @return true if the TypedSlot object has been allocated a slot.
+   */
+  bool hasSlot() const { return slot_ != nullptr; }
+
+  /**
+   * @param slot The allocated slot object. Ownership transferred into the TypedSlot.
+   */
+  void setSlot(SlotPtr&& slot) { slot_ = std::move(slot); }
+
+  /**
+   * Returns if there is thread local data for this thread.
+   *
+   * This should return true for Envoy worker threads and false for threads which do not have thread
+   * local storage allocated.
+   *
+   * @return true if registerThread has been called for this thread, false otherwise.
+   */
+  bool currentThreadRegistered() { return slot_->currentThreadRegistered(); }
+
+  /**
+   * Set thread local data on all threads previously registered via registerThread().
+   * @param initializeCb supplies the functor that will be called *on each thread*. The functor
+   *                     returns the thread local object which is then stored. The storage is via
+   *                     a shared_ptr. Thus, this is a flexible mechanism that can be used to share
+   *                     the same data across all threads or to share different data on each thread.
+   *
+   * NOTE: The initialize callback is not supposed to capture the Slot, or its owner. As the owner
+   * may be destructed in main thread before the update_cb gets called in a worker thread.
+   */
+  using SharedT = std::shared_ptr<T>;
+  using InitializeCb = std::function<SharedT(Event::Dispatcher& dispatcher)>;
+  void set(InitializeCb cb) { slot_->set(cb); }
+
+  /**
+   * @return a reference to the thread local object.
+   */
+  T& get() { return slot_->getTyped<T>(); }
+
+  /**
+   * @return a pointer to the thread local object.
+   */
+  T* operator->() { return &get(); }
+
+  /**
+   * UpdateCb is passed a mutable reference to the current stored data.
+   *
+   * NOTE: The update callback is not supposed to capture the TypedSlot, or its owner. As the owner
+   * may be destructed in main thread before the update_cb gets called in a worker thread.
+   */
+  using UpdateCb = std::function<void(T& obj)>;
+  void runOnAllThreads(const UpdateCb& cb) { slot_->runOnAllThreads(makeSlotUpdateCb(cb)); }
+  void runOnAllThreads(const UpdateCb& cb, Event::PostCb complete_cb) {
+    slot_->runOnAllThreads(makeSlotUpdateCb(cb), complete_cb);
+  }
+
+private:
+  Slot::UpdateCb makeSlotUpdateCb(UpdateCb cb) {
+    return [cb](ThreadLocalObjectSharedPtr obj) -> ThreadLocalObjectSharedPtr {
+      T& typed_obj = obj->asType<T>();
+      cb(typed_obj);
+      // Note: Better have a test for mutating the object.
+      return obj;
+    };
+  }
+
+  SlotPtr slot_;
+};
+
 /**
  * Interface used to allocate thread local slots.
  */

source/common/stats/thread_local_store.cc

@@ -185,10 +185,9 @@ void ThreadLocalStoreImpl::initializeThreading(Event::Dispatcher& main_thread_di
                                                ThreadLocal::Instance& tls) {
   threading_ever_initialized_ = true;
   main_thread_dispatcher_ = &main_thread_dispatcher;
-  tls_ = tls.allocateSlot();
-  tls_->set([](Event::Dispatcher&) -> ThreadLocal::ThreadLocalObjectSharedPtr {
-    return std::make_shared<TlsCache>();
-  });
+  tls_cache_.setSlot(tls.allocateSlot());
+  tls_cache_.set(
+      [](Event::Dispatcher&) -> std::shared_ptr<TlsCache> { return std::make_shared<TlsCache>(); });
 }
 
 void ThreadLocalStoreImpl::shutdownThreading() {
@@ -205,14 +204,12 @@ void ThreadLocalStoreImpl::mergeHistograms(PostMergeCb merge_complete_cb) {
   if (!shutting_down_) {
     ASSERT(!merge_in_progress_);
     merge_in_progress_ = true;
-    tls_->runOnAllThreads(
-        [](ThreadLocal::ThreadLocalObjectSharedPtr object)
-            -> ThreadLocal::ThreadLocalObjectSharedPtr {
-          for (const auto& id_hist : object->asType<TlsCache>().tls_histogram_cache_) {
+    tls_cache_.runOnAllThreads(
+        [](TlsCache& tls_cache) {
+          for (const auto& id_hist : tls_cache.tls_histogram_cache_) {
             const TlsHistogramSharedPtr& tls_hist = id_hist.second;
             tls_hist->beginMerge();
           }
-          return object;
         },
         [this, merge_complete_cb]() -> void { mergeInternal(merge_complete_cb); });
   } else {
@@ -305,12 +302,8 @@ void ThreadLocalStoreImpl::clearScopeFromCaches(uint64_t scope_id,
   // at the same time.
   if (!shutting_down_) {
     // Perform a cache flush on all threads.
-    tls_->runOnAllThreads(
-        [scope_id](ThreadLocal::ThreadLocalObjectSharedPtr object)
-            -> ThreadLocal::ThreadLocalObjectSharedPtr {
-          object->asType<TlsCache>().eraseScope(scope_id);
-          return object;
-        },
+    tls_cache_.runOnAllThreads(
+        [scope_id](TlsCache& tls_cache) { tls_cache.eraseScope(scope_id); },
         [central_cache]() { /* Holds onto central_cache until all tls caches are clear */ });
   }
 }
@@ -326,11 +319,8 @@ void ThreadLocalStoreImpl::clearHistogramFromCaches(uint64_t histogram_id) {
     // https://gist.github.com/jmarantz/838cb6de7e74c0970ea6b63eded0139a
     // contains a patch that will implement batching together to clear multiple
     // histograms.
-    tls_->runOnAllThreads([histogram_id](ThreadLocal::ThreadLocalObjectSharedPtr object)
-                              -> ThreadLocal::ThreadLocalObjectSharedPtr {
-      object->asType<TlsCache>().eraseHistogram(histogram_id);
-      return object;
-    });
+    tls_cache_.runOnAllThreads(
+        [histogram_id](TlsCache& tls_cache) { tls_cache.eraseHistogram(histogram_id); });
   }
 }
 
@@ -498,8 +488,8 @@ Counter& ThreadLocalStoreImpl::ScopeImpl::counterFromStatNameWithTags(
   // initialized currently.
   StatRefMap<Counter>* tls_cache = nullptr;
   StatNameHashSet* tls_rejected_stats = nullptr;
-  if (!parent_.shutting_down_ && parent_.tls_) {
-    TlsCacheEntry& entry = parent_.tls_->getTyped<TlsCache>().insertScope(this->scope_id_);
+  if (!parent_.shutting_down_ && parent_.tls_cache_.hasSlot()) {
+    TlsCacheEntry& entry = parent_.tls_cache_->insertScope(this->scope_id_);
     tls_cache = &entry.counters_;
     tls_rejected_stats = &entry.rejected_stats_;
   }
@@ -550,8 +540,8 @@ Gauge& ThreadLocalStoreImpl::ScopeImpl::gaugeFromStatNameWithTags(
 
   StatRefMap<Gauge>* tls_cache = nullptr;
   StatNameHashSet* tls_rejected_stats = nullptr;
-  if (!parent_.shutting_down_ && parent_.tls_) {
-    TlsCacheEntry& entry = parent_.tls_->getTyped<TlsCache>().scope_cache_[this->scope_id_];
+  if (!parent_.shutting_down_ && parent_.tls_cache_.hasSlot()) {
+    TlsCacheEntry& entry = parent_.tls_cache_->scope_cache_[this->scope_id_];
     tls_cache = &entry.gauges_;
     tls_rejected_stats = &entry.rejected_stats_;
   }
@@ -588,8 +578,8 @@ Histogram& ThreadLocalStoreImpl::ScopeImpl::histogramFromStatNameWithTags(
 
   StatNameHashMap<ParentHistogramSharedPtr>* tls_cache = nullptr;
   StatNameHashSet* tls_rejected_stats = nullptr;
-  if (!parent_.shutting_down_ && parent_.tls_) {
-    TlsCacheEntry& entry = parent_.tls_->getTyped<TlsCache>().scope_cache_[this->scope_id_];
+  if (!parent_.shutting_down_ && parent_.tls_cache_.hasSlot()) {
+    TlsCacheEntry& entry = parent_.tls_cache_->scope_cache_[this->scope_id_];
     tls_cache = &entry.parent_histograms_;
     auto iter = tls_cache->find(final_stat_name);
     if (iter != tls_cache->end()) {
@@ -666,8 +656,8 @@ TextReadout& ThreadLocalStoreImpl::ScopeImpl::textReadoutFromStatNameWithTags(
   // initialized currently.
   StatRefMap<TextReadout>* tls_cache = nullptr;
   StatNameHashSet* tls_rejected_stats = nullptr;
-  if (!parent_.shutting_down_ && parent_.tls_) {
-    TlsCacheEntry& entry = parent_.tls_->getTyped<TlsCache>().insertScope(this->scope_id_);
+  if (!parent_.shutting_down_ && parent_.tls_cache_.hasSlot()) {
+    TlsCacheEntry& entry = parent_.tls_cache_->insertScope(this->scope_id_);
     tls_cache = &entry.text_readouts_;
     tls_rejected_stats = &entry.rejected_stats_;
   }
@@ -712,8 +702,8 @@ Histogram& ThreadLocalStoreImpl::tlsHistogram(ParentHistogramImpl& parent, uint6
   // See comments in counterFromStatName() which explains the logic here.
 
   TlsHistogramSharedPtr* tls_histogram = nullptr;
-  if (!shutting_down_ && tls_ != nullptr) {
-    TlsCache& tls_cache = tls_->getTyped<TlsCache>();
+  if (!shutting_down_ && tls_cache_.hasSlot()) {
+    TlsCache& tls_cache = tls_cache_.get();
     tls_histogram = &tls_cache.tls_histogram_cache_[id];
     if (*tls_histogram != nullptr) {
       return **tls_histogram;

source/common/stats/thread_local_store.h

@@ -480,7 +480,7 @@ class ThreadLocalStoreImpl : Logger::Loggable<Logger::Id::stats>, public StoreRo
 
   Allocator& alloc_;
   Event::Dispatcher* main_thread_dispatcher_{};
-  ThreadLocal::SlotPtr tls_;
+  ThreadLocal::TypedSlot<TlsCache> tls_cache_;
   mutable Thread::MutexBasicLockable lock_;
   absl::flat_hash_set<ScopeImpl*> scopes_ ABSL_GUARDED_BY(lock_);
   ScopePtr default_scope_;

test/common/stats/thread_local_store_test.cc

@@ -54,12 +54,9 @@ class ThreadLocalStoreTestingPeer {
   static void numTlsHistograms(ThreadLocalStoreImpl& thread_local_store_impl,
                                const std::function<void(uint32_t)>& num_tls_hist_cb) {
     auto num_tls_histograms = std::make_shared<std::atomic<uint32_t>>(0);
-    thread_local_store_impl.tls_->runOnAllThreads(
-        [num_tls_histograms](ThreadLocal::ThreadLocalObjectSharedPtr object)
-            -> ThreadLocal::ThreadLocalObjectSharedPtr {
-          auto& tls_cache = object->asType<ThreadLocalStoreImpl::TlsCache>();
+    thread_local_store_impl.tls_cache_.runOnAllThreads(
+        [num_tls_histograms](ThreadLocalStoreImpl::TlsCache& tls_cache) {
           *num_tls_histograms += tls_cache.tls_histogram_cache_.size();
-          return object;
         },
         [num_tls_hist_cb, num_tls_histograms]() { num_tls_hist_cb(*num_tls_histograms); });
   }