lokinet/llarp/util/metrics_core.hpp

#ifndef LLARP_METRICS_CORE_HPP
#define LLARP_METRICS_CORE_HPP

#include <util/metrics_types.hpp>
#include <util/scheduler.hpp>
#include <util/stopwatch.hpp>
#include <util/threading.hpp>

#include <map>
#include <memory>
#include <utility>
#include <vector>

namespace llarp
{
  namespace metrics
  {
    inline void
    packToTagsImpl(Tags &)
    {
    }

    template < typename K, typename V, typename... Args >
    inline void
    packToTagsImpl(Tags &tags, const K &k, const V &v, const Args &... args)
    {
      static_assert(std::is_convertible< K, Tag >::value, "");
      static_assert(std::is_convertible< V, TagValue >::value, "");

      tags.emplace(k, v);
      packToTagsImpl(tags, args...);
    }

    template < typename... Args >
    inline Tags
    packToTags(const Args &... args)
    {
      static_assert(sizeof...(args) % 2 == 0, "");
      Tags tags;
      packToTagsImpl(tags, args...);
      return tags;
    }

    template <>
    inline Tags
    packToTags< Tags >(const Tags &tags)
    {
      return tags;
    }

    template < typename Type >
    class Collector
    {
     public:
      using RecordType        = Record< Type >;
      using TaggedRecordsType = TaggedRecords< Type >;

     private:
      TaggedRecordsType m_records GUARDED_BY(m_mutex);
      mutable util::Mutex m_mutex;  // protects m_records

      Collector(const Collector &) = delete;
      Collector &
      operator=(const Collector &) = delete;

      template < typename... Args >
      RecordType &
      fetch(Args... args) EXCLUSIVE_LOCKS_REQUIRED(m_mutex)
      {
        return m_records.data[packToTags(args...)];
      }

     public:
      Collector(const Id &id) : m_records(id)
      {
      }

      void
      clear()
      {
        absl::MutexLock l(&m_mutex);
        m_records.data.clear();
      }

      TaggedRecordsType
      loadAndClear()
      {
        absl::MutexLock l(&m_mutex);
        auto result = m_records;
        m_records.data.clear();

        return result;
      }

      TaggedRecordsType
      load()
      {
        absl::MutexLock l(&m_mutex);
        return m_records;
      }

      template < typename... Args >
      void
      tick(Type value, Args... args)
      {
        absl::MutexLock l(&m_mutex);
        RecordType &rec = fetch(args...);
        rec.count()++;
        rec.total() += value;
        rec.min() = std::min(rec.min(), value);
        rec.max() = std::max(rec.max(), value);
      }

      template < typename... Args >
      void
      accumulate(size_t count, Type total, Type min, Type max, Args... args)
      {
        absl::MutexLock l(&m_mutex);
        RecordType &rec = fetch(args...);
        rec.count() += count;
        rec.total() += total;
        rec.min() = std::min(rec.min(), min);
        rec.max() = std::max(rec.max(), max);
      }

      template < typename... Args >
      void
      set(size_t count, Type total, Type min, Type max, Args... args)
      {
        absl::MutexLock l(&m_mutex);
        RecordType &rec = fetch(args...);
        rec.count()     = count;
        rec.total()     = total;
        rec.min()       = min;
        rec.max()       = max;
      }

      const Id &
      id() const
      {
        return m_records.id;
      }
    };

    using IntCollector    = Collector< int >;
    using DoubleCollector = Collector< double >;

    class Publisher
    {
     public:
      virtual ~Publisher() = default;

      virtual void
      publish(const Sample &sample) = 0;
    };

    template < typename Value >
    static inline void
    combine(TaggedRecords< Value > &records,
            const TaggedRecords< Value > &toAdd)
    {
      records.id = toAdd.id;
      for(auto &record : records.data)
      {
        auto it = toAdd.data.find(record.first);
        if(it == toAdd.data.end())
        {
          continue;
        }

        record.second.count() += it->second.count();
        record.second.total() += it->second.total();
        record.second.min() = std::min(record.second.min(), it->second.min());
        record.second.max() = std::max(record.second.max(), it->second.max());
      }

      for(const auto &record : toAdd.data)
      {
        auto it = records.data.find(record.first);
        if(it != records.data.end())
        {
          continue;
        }

        records.data[record.first] = record.second;
      }
    }

    template < typename Type >
    class Collectors
    {
      using CollectorType = Collector< Type >;
      using CollectorPtr  = std::shared_ptr< CollectorType >;
      using CollectorSet  = std::set< CollectorPtr >;

      CollectorType m_default;
      CollectorSet m_collectors;

      Collectors(const Collectors &) = delete;
      Collectors &
      operator=(const Collectors &) = delete;

     public:
      Collectors(const Id &id) : m_default(id)
      {
      }

      CollectorType *
      defaultCollector()
      {
        return &m_default;
      }

      std::shared_ptr< CollectorType >
      add()
      {
        auto ptr = std::make_shared< CollectorType >(m_default.id());
        m_collectors.insert(ptr);
        return ptr;
      }

      bool
      remove(CollectorType *collector)
      {
        std::shared_ptr< CollectorType > ptr(collector, [](CollectorType *) {});
        size_t count = m_collectors.erase(ptr);
        return count > 0;
      }

      TaggedRecords< Type >
      combineAndClear()
      {
        TaggedRecords< Type > rec = m_default.loadAndClear();

        for(auto &ptr : m_collectors)
        {
          metrics::combine(rec, ptr->loadAndClear());
        }

        return rec;
      }

      TaggedRecords< Type >
      combine()
      {
        TaggedRecords< Type > rec = m_default.load();

        for(auto &ptr : m_collectors)
        {
          metrics::combine(rec, ptr->load());
        }
        return rec;
      }

      std::vector< std::shared_ptr< CollectorType > >
      collectors() const
      {
        return std::vector< std::shared_ptr< CollectorType > >(
            m_collectors.begin(), m_collectors.end());
      }

      const Id &
      id() const
      {
        return m_default.id();
      }
    };

    using DoubleCollectors = Collectors< double >;
    using IntCollectors    = Collectors< int >;

    class Registry
    {
      using NamedCategory = std::tuple< string_view, string_view >;

      using MetricMap =
          std::map< NamedCategory, std::shared_ptr< Description > >;
      using CategoryMap = std::map< string_view, std::shared_ptr< Category > >;

      std::set< std::string > m_stringmem GUARDED_BY(m_mutex);
      CategoryMap m_categories GUARDED_BY(m_mutex);
      MetricMap m_metrics GUARDED_BY(m_mutex);
      bool m_defaultEnabled GUARDED_BY(m_mutex){true};
      mutable util::Mutex m_mutex;  // protects m_stringmem, m_categories,
                                    // m_metrics, m_defaultEnabled

      Registry(const Registry &) = delete;
      Registry &
      operator=(const Registry &) = delete;

      std::pair< Id, bool >
      insert(string_view category, string_view name)
          EXCLUSIVE_LOCKS_REQUIRED(m_mutex);

     public:
      Registry() = default;

      Id
      add(string_view category, string_view name) LOCKS_EXCLUDED(m_mutex);
      Id
      get(string_view category, string_view name) LOCKS_EXCLUDED(m_mutex);

      const Category *
      add(string_view category) LOCKS_EXCLUDED(m_mutex);
      const Category *
      get(string_view category);

      void
      enable(const Category *category, bool value);
      void
      enableAll(bool value);

      void
      registerContainer(const Category *category, CategoryContainer &container);
      void
      publicationType(const Id &id, Publication::Type type);
      void
      setFormat(const Id &id, const Format &format);

      size_t
      metricCount() const
      {
        absl::ReaderMutexLock l(&m_mutex);
        return m_metrics.size();
      }
      size_t
      categoryCount() const
      {
        absl::ReaderMutexLock l(&m_mutex);
        return m_categories.size();
      }

      const Category *
      findCategory(string_view category) const;
      Id
      findId(string_view category, string_view name) const;

      std::vector< const Category * >
      getAll() const;
    };

    using DoubleRecords = std::vector< TaggedRecords< double > >;
    using IntRecords    = std::vector< TaggedRecords< int > >;

    struct Records
    {
      DoubleRecords doubleRecords;
      IntRecords intRecords;

      Records() = default;

      Records(DoubleRecords d, IntRecords i)
          : doubleRecords(std::move(d)), intRecords(std::move(i))
      {
      }
    };

    inline bool
    operator==(const Records &lhs, const Records &rhs)
    {
      return std::tie(lhs.doubleRecords, lhs.intRecords)
          == std::tie(rhs.doubleRecords, rhs.intRecords);
    }

    template < typename Type >
    class CollectorRepo
    {
      using CollectorsPtr = std::shared_ptr< Collectors< Type > >;
      using IdCollectors  = std::map< Id, CollectorsPtr >;
      using CategoryCollectors =
          std::map< const Category *, std::vector< Collectors< Type > * > >;

      Registry *m_registry;
      IdCollectors m_collectors;
      CategoryCollectors m_categories GUARDED_BY(m_mutex);

      mutable util::Mutex m_mutex;  // protects m_categories

      CollectorRepo(const CollectorRepo &) = delete;
      CollectorRepo &
      operator=(const CollectorRepo &) = delete;

      Collectors< Type > &
      getCollectors(const Id &id) SHARED_LOCKS_REQUIRED(m_mutex)
      {
        auto it = m_collectors.find(id);

        if(it == m_collectors.end())
        {
          assert(id.valid());

          const Category *cat = id.category();

          auto ptr  = std::make_shared< Collectors< Type > >(id);
          auto &vec = m_categories[cat];
          vec.reserve(vec.size() + 1);

          it = m_collectors.emplace(id, ptr).first;
          vec.push_back(ptr.get());
        }

        return *it->second.get();
      }

      template < TaggedRecords< Type > (Collectors< Type >::*func)() >
      std::vector< TaggedRecords< Type > >
      collectOp(const Category *category) LOCKS_EXCLUDED(m_mutex)
      {
        absl::WriterMutexLock l(&m_mutex);

        auto it = m_categories.find(category);

        if(it == m_categories.end())
        {
          return {};
        }

        std::vector< TaggedRecords< Type > > result;
        auto &collectors = it->second;
        result.reserve(collectors.size());

        std::transform(collectors.begin(), collectors.end(),
                       std::back_inserter(result),
                       [](auto &collector) { return (collector->*func)(); });

        return result;
      }

     public:
      explicit CollectorRepo(Registry *registry) : m_registry(registry)
      {
      }

      std::vector< TaggedRecords< Type > >
      collectAndClear(const Category *category)
      {
        return collectOp< &Collectors< Type >::combineAndClear >(category);
      }

      std::vector< TaggedRecords< Type > >
      collect(const Category *category)
      {
        return collectOp< &Collectors< Type >::combine >(category);
      }

      Collector< Type > *
      defaultCollector(string_view category, string_view name)
      {
        return defaultCollector(m_registry->get(category, name));
      }

      Collector< Type > *
      defaultCollector(const Id &id) LOCKS_EXCLUDED(m_mutex)
      {
        {
          absl::ReaderMutexLock l(&m_mutex);
          auto it = m_collectors.find(id);
          if(it != m_collectors.end())
          {
            return it->second->defaultCollector();
          }
        }

        {
          absl::WriterMutexLock l(&m_mutex);
          return getCollectors(id).defaultCollector();
        }
      }

      std::shared_ptr< Collector< Type > >
      addCollector(string_view category, string_view name)
      {
        return addCollector(m_registry->get(category, name));
      }

      std::shared_ptr< Collector< Type > >
      addCollector(const Id &id) LOCKS_EXCLUDED(m_mutex)
      {
        absl::WriterMutexLock l(&m_mutex);
        return getCollectors(id).add();
      }

      std::vector< std::shared_ptr< Collector< Type > > >
      allCollectors(const Id &id) LOCKS_EXCLUDED(m_mutex)
      {
        absl::ReaderMutexLock l(&m_mutex);

        auto it = m_collectors.find(id);

        if(it == m_collectors.end())
        {
          return {};
        }

        return it->second->collectors();
      }

      Registry &
      registry()
      {
        return *m_registry;
      }

      const Registry &
      registry() const
      {
        return *m_registry;
      }
    };

    class Manager;

    class PublisherRegistry
    {
      using PubPtr        = std::shared_ptr< Publisher >;
      using CatPublishers = std::multimap< const Category *, PubPtr >;
      using PubSet        = std::set< PubPtr >;
      using PubReg  = std::map< const Category *, CatPublishers::iterator >;
      using RegInfo = std::map< PubPtr, PubReg >;

      CatPublishers m_categoryPublishers;
      RegInfo m_registry;
      PubSet m_publishers;

      PublisherRegistry(const PublisherRegistry &) = delete;
      PublisherRegistry &
      operator=(const PublisherRegistry &) = delete;

     public:
      using GlobalIterator = PubSet::iterator;
      using CatIterator    = CatPublishers::iterator;

      PublisherRegistry() = default;

      bool
      addGlobalPublisher(const std::shared_ptr< Publisher > &publisher)
      {
        if(m_publishers.find(publisher) != m_publishers.end())
        {
          return false;
        }
        if(m_registry.find(publisher) != m_registry.end())
        {
          return false;
        }

        m_publishers.insert(publisher);
        return true;
      }

      bool
      addPublisher(const Category *category,
                   const std::shared_ptr< Publisher > &publisher)
      {
        if(m_publishers.find(publisher) != m_publishers.end())
        {
          return false;
        }

        auto &reg = m_registry[publisher];
        if(reg.find(category) != reg.end())
        {
          return false;
        }

        auto it = m_categoryPublishers.emplace(category, publisher);
        reg.emplace(category, it);
        return true;
      }

      bool
      removePublisher(const Publisher *publisher)
      {
        std::shared_ptr< Publisher > ptr(const_cast< Publisher * >(publisher),
                                         [](Publisher *) {});

        auto allIt = m_publishers.find(ptr);

        if(allIt != m_publishers.end())
        {
          m_publishers.erase(allIt);
          return true;
        }

        auto regIt = m_registry.find(ptr);
        if(regIt == m_registry.end())
        {
          return false;
        }

        for(auto &spec : regIt->second)
        {
          m_categoryPublishers.erase(spec.second);
        }

        m_registry.erase(regIt);
        return true;
      }

      GlobalIterator
      globalBegin()
      {
        return m_publishers.begin();
      }
      GlobalIterator
      globalEnd()
      {
        return m_publishers.end();
      }

      CatIterator
      catBegin()
      {
        return m_categoryPublishers.begin();
      }
      CatIterator
      catEnd()
      {
        return m_categoryPublishers.end();
      }

      CatIterator
      lowerBound(const Category *category)
      {
        return m_categoryPublishers.lower_bound(category);
      }
      CatIterator
      upperBound(const Category *category)
      {
        return m_categoryPublishers.upper_bound(category);
      }

      std::vector< Publisher * >
      globalPublishers() const
      {
        std::vector< Publisher * > result;
        result.reserve(m_publishers.size());

        std::transform(m_publishers.begin(), m_publishers.end(),
                       std::back_inserter(result),
                       [](const auto &p) { return p.get(); });

        return result;
      }

      std::vector< Publisher * >
      catPublishers(const Category *category) const
      {
        std::vector< Publisher * > result;
        auto beg = m_categoryPublishers.lower_bound(category);
        auto end = m_categoryPublishers.upper_bound(category);
        result.reserve(std::distance(beg, end));

        std::transform(beg, end, std::back_inserter(result),
                       [](const auto &p) { return p.second.get(); });

        return result;
      }
    };

    struct PublisherHelper;

    /// The big dog.
    /// This class owns everything else, and is responsible for managing the
    /// gathering and publishing of metrics
    class Manager
    {
     public:
      // Public callback. If the bool flag is true, clear the metrics back to
      // their default state.
      using Handle = uint64_t;

     private:
      // Map categories to the times they were last reset
      using ResetTimes = std::map< const Category *, absl::Duration >;

      friend struct PublisherHelper;

      Registry m_registry;
      CollectorRepo< double > m_doubleRepo;
      CollectorRepo< int > m_intRepo;
      PublisherRegistry m_publishers GUARDED_BY(m_mutex);

      const absl::Duration m_createTime;
      ResetTimes m_resetTimes;

      util::Mutex m_publishLock ACQUIRED_BEFORE(m_mutex);
      mutable util::Mutex m_mutex ACQUIRED_AFTER(m_publishLock);

     public:
      static constexpr Handle INVALID_HANDLE =
          std::numeric_limits< Handle >::max();

      Manager()
          : m_doubleRepo(&m_registry)
          , m_intRepo(&m_registry)
          , m_createTime(absl::Now() - absl::UnixEpoch())
      {
      }

      /// Add a `publisher` which will receive all events
      bool
      addGlobalPublisher(const std::shared_ptr< Publisher > &publisher)
      {
        absl::WriterMutexLock l(&m_mutex);
        return m_publishers.addGlobalPublisher(publisher);
      }

      /// Add a `publisher` which will receive events for the given
      /// `categoryName` only
      bool
      addPublisher(string_view categoryName,
                   const std::shared_ptr< Publisher > &publisher)
      {
        return addPublisher(m_registry.get(categoryName), publisher);
      }
      /// Add a `publisher` which will receive events for the given
      /// `category` only
      bool
      addPublisher(const Category *category,
                   const std::shared_ptr< Publisher > &publisher)
      {
        absl::WriterMutexLock l(&m_mutex);
        return m_publishers.addPublisher(category, publisher);
      }

      bool
      removePublisher(const Publisher *publisher)
      {
        absl::WriterMutexLock l(&m_mutex);
        return m_publishers.removePublisher(publisher);
      }
      bool
      removePublisher(const std::shared_ptr< Publisher > &publisher)
      {
        absl::WriterMutexLock l(&m_mutex);
        return m_publishers.removePublisher(publisher.get());
      }

      // clang-format off
      CollectorRepo<double>&       doubleCollectorRepo()       { return m_doubleRepo; }
      CollectorRepo<int>&       intCollectorRepo()       { return m_intRepo; }
      Registry&            registry()            { return m_registry; }
      const Registry&      registry() const      { return m_registry; }
      // clang-format on

      /// Publish specific categories of metric matching the category/categories
      Sample
      collectSample(Records &records, bool clear = false)
      {
        std::vector< const Category * > allCategories = m_registry.getAll();
        return collectSample(
            records, absl::Span< const Category * >{allCategories}, clear);
      }

      Sample
      collectSample(Records &records, absl::Span< const Category * > categories,
                    bool clear = false);

      /// Publish specific categories of metric matching the category/categories
      void
      publish(const Category *category, bool clear = true)
      {
        publish(absl::Span< const Category * >(&category, 1), clear);
      }
      void
      publish(absl::Span< const Category * > categories, bool clear = true);
      void
      publish(const std::set< const Category * > &categories,
              bool clear = true);

      void
      publishAll(bool clear = true)
      {
        std::vector< const Category * > allCategories = m_registry.getAll();
        publish(absl::Span< const Category * >{allCategories}, clear);
      }

      void
      publishAllExcluding(const std::set< const Category * > &excludeCategories,
                          bool clear = true)
      {
        if(excludeCategories.empty())
        {
          publishAll(clear);
          return;
        }

        std::vector< const Category * > allCategories = m_registry.getAll();
        std::vector< const Category * > includedCategories;
        includedCategories.reserve(allCategories.size()
                                   - excludeCategories.size());

        std::copy_if(
            allCategories.begin(), allCategories.end(),
            std::back_inserter(includedCategories), [&](const Category *cat) {
              return excludeCategories.end() == excludeCategories.find(cat);
            });

        if(!includedCategories.empty())
        {
          publish(absl::Span< const Category * >{includedCategories}, clear);
        }
      }

      void
      enableCategory(string_view categoryName, bool enable = true)
      {
        m_registry.enable(m_registry.get(categoryName), enable);
      }
      void
      enableCategory(const Category *category, bool enable = true)
      {
        m_registry.enable(category, enable);
      }

      void
      enableAll(bool enable)
      {
        m_registry.enableAll(enable);
      }

      std::vector< Publisher * >
      globalPublishers() const
      {
        absl::ReaderMutexLock l(&m_mutex);
        return m_publishers.globalPublishers();
      }

      std::vector< Publisher * >
      publishersForCategory(string_view categoryName) const
      {
        const Category *category = m_registry.findCategory(categoryName);
        return category ? publishersForCategory(category)
                        : std::vector< Publisher * >();
      }
      std::vector< Publisher * >
      publishersForCategory(const Category *category) const
      {
        absl::ReaderMutexLock l(&m_mutex);
        return m_publishers.catPublishers(category);
      }
    };

    /// Provide a handy mechanism for retrieving the default manager, without
    /// a painful singleton mechanism
    class DefaultManager
    {
      static Manager *m_manager;

     public:
      static Manager *
      instance()
      {
        return m_manager;
      }

      static Manager *
      manager(Manager *value)
      {
        return value ? value : m_manager;
      }

      static Manager *
      create()
      {
        m_manager = new Manager;
        return m_manager;
      }

      static void
      destroy()
      {
        delete m_manager;
        m_manager = nullptr;
      }
    };

    /// Scoped guard to manage the default manager
    class DefaultManagerGuard
    {
      DefaultManagerGuard(const DefaultManagerGuard &) = delete;
      DefaultManagerGuard &
      operator=(const DefaultManagerGuard &) = delete;

     public:
      DefaultManagerGuard()
      {
        DefaultManager::create();
      }

      ~DefaultManagerGuard()
      {
        DefaultManager::destroy();
      }

      Manager *
      instance()
      {
        return DefaultManager::instance();
      }
    };

    template < typename Collector, typename Value,
               CollectorRepo< Value > &(Manager::*repoFunc)() >
    class Metric
    {
      Collector *m_collector;  // can be null
      const std::atomic_bool *m_enabled;

     public:
      static Collector *
      lookup(string_view category, string_view name, Manager *manager = nullptr)
      {
        manager = DefaultManager::manager(manager);
        return manager ? (manager->*repoFunc)().defaultCollector(category, name)
                       : nullptr;
      }

      static Collector *
      lookup(const Id &id, Manager *manager = nullptr)
      {
        manager = DefaultManager::manager(manager);
        return manager ? (manager->*repoFunc)().defaultCollector(id) : 0;
      }

      Metric(string_view category, string_view name, Manager *manager)
          : m_collector(lookup(category, name, manager))
          , m_enabled(m_collector ? &m_collector->id().category()->enabledRaw()
                                  : nullptr)
      {
      }

      Metric(const Id &id, Manager *manager)
          : m_collector(lookup(id, manager))
          , m_enabled(m_collector ? &m_collector->id().category()->enabledRaw()
                                  : nullptr)
      {
      }

      Metric(Collector *collector)
          : m_collector(collector)
          , m_enabled(m_collector ? &m_collector->id().category()->enabledRaw()
                                  : nullptr)
      {
      }

      bool
      active() const
      {
        return m_enabled ? m_enabled->load(std::memory_order_relaxed) : false;
      }

      void
      tick()
      {
        if(active())
        {
          m_collector->tick(static_cast< Value >(1));
        }
      }

      void
      update(Value val)
      {
        if(active())
        {
          m_collector->tick(val);
        }
      }

      void
      accumulate(size_t count, Value total, Value min, Value max)
      {
        if(active())
        {
          m_collector->accumulate(count, total, min, max);
        }
      }

      void
      set(size_t count, Value total, Value min, Value max)
      {
        if(active())
        {
          m_collector->set(count, total, min, max);
        }
      }

      Id
      id() const
      {
        return m_collector ? m_collector->id() : Id();
      }

      const Collector *
      collector() const
      {
        return m_collector;
      }

      Collector *
      collector()
      {
        return m_collector;
      }

      static void
      getCollector(Collector **collector, CategoryContainer *container,
                   string_view category, string_view metric)
      {
        Manager *manager = DefaultManager::instance();
        *collector = (manager->*repoFunc().defaultCollector)(category, metric);
        manager->registry().registerContainer((*collector)->id().category(),
                                              container);
      }

      static void
      getCollector(Collector **collector, CategoryContainer *container,
                   string_view category, string_view metric,
                   Publication::Type type)
      {
        Manager *manager = DefaultManager::instance();
        *collector = (manager->*repoFunc().defaultCollector)(category, metric);
        manager->registry().registerContainer((*collector)->id().category(),
                                              container);
        manager->registry().publicationType((*collector)->id(), type);
      }
    };

    using DoubleMetric =
        Metric< DoubleCollector, double, &Manager::doubleCollectorRepo >;

    using IntMetric = Metric< IntCollector, int, &Manager::intCollectorRepo >;

    class TimerGuard
    {
     private:
      Tags m_tags;
      util::Stopwatch m_stopwatch;
      DoubleCollector *m_collector;

      TimerGuard(const TimerGuard &) = delete;
      TimerGuard &
      operator=(const TimerGuard &) = delete;

     public:
      template < typename... TagVals >
      TimerGuard(DoubleMetric *metric, TagVals &&... tags)
          : m_tags(packToTags(tags...))
          , m_collector(metric->active() ? metric->collector() : nullptr)
      {
        if(m_collector)
        {
          m_stopwatch.start();
        }
      }

      template < typename... TagVals >
      TimerGuard(DoubleCollector *collector, TagVals &&... tags)
          : m_tags(packToTags(tags...))
          , m_collector(collector && collector->id().category()->enabled()
                            ? collector
                            : nullptr)
      {
        if(m_collector)
        {
          m_stopwatch.start();
        }
      }

      template < typename... TagVals >
      TimerGuard(string_view category, string_view name,
                 Manager *manager = nullptr, TagVals &&... tags)
          : m_tags(packToTags(tags...)), m_collector(nullptr)
      {
        DoubleCollector *collector =
            DoubleMetric::lookup(category, name, manager);
        m_collector = (collector && collector->id().category()->enabled())
            ? collector
            : nullptr;
        if(m_collector)
        {
          m_stopwatch.start();
        }
      }

      template < typename... TagVals >
      TimerGuard(const Id &id, Manager *manager = nullptr, TagVals &&... tags)
          : m_tags(packToTags(tags...)), m_collector(nullptr)
      {
        DoubleCollector *collector = DoubleMetric::lookup(id, manager);
        m_collector = (collector && collector->id().category()->enabled())
            ? collector
            : nullptr;
        if(m_collector)
        {
          m_stopwatch.start();
        }
      }

      ~TimerGuard()
      {
        if(active())
        {
          m_stopwatch.stop();
          m_collector->tick(absl::ToDoubleSeconds(m_stopwatch.time()), m_tags);
        }
      }

      bool
      active() const
      {
        return m_collector ? m_collector->id().category()->enabled() : false;
      }
    };

    struct PublisherSchedulerData;

    class PublisherScheduler
    {
      friend class PublisherSchedulerGuard;

      using Categories = std::map< const Category *, absl::Duration >;
      using Repeaters =
          std::map< absl::Duration, std::shared_ptr< PublisherSchedulerData > >;

      thread::Scheduler &m_scheduler;
      Manager *m_manager;

      Categories m_categories GUARDED_BY(m_mutex);
      Repeaters m_repeaters GUARDED_BY(m_mutex);
      absl::Duration m_defaultInterval GUARDED_BY(m_mutex);

      mutable util::Mutex
          m_mutex;  // protected m_categories, m_repeaters, m_defaultInterval

      void
      publish(const std::shared_ptr< PublisherSchedulerData > &data) const;

      void
      cancel(Categories::iterator it) EXCLUSIVE_LOCKS_REQUIRED(m_mutex);

      bool
      cancelDefault() EXCLUSIVE_LOCKS_REQUIRED(m_mutex);

     public:
      PublisherScheduler(thread::Scheduler &scheduler, Manager *manager)
          : m_scheduler(scheduler), m_manager(manager), m_defaultInterval()
      {
      }

      ~PublisherScheduler()
      {
        cancelAll();
      }

      void
      schedule(string_view categoryName, absl::Duration interval)
      {
        return schedule(m_manager->registry().get(categoryName), interval);
      }

      void
      schedule(const Category *category, absl::Duration interval);

      void
      setDefault(absl::Duration interval);

      bool
      cancel(string_view categoryName)
      {
        return cancel(m_manager->registry().get(categoryName));
      }

      bool
      cancel(const Category *category);

      bool
      clearDefault();

      void
      cancelAll();

      Manager *
      manager()
      {
        return m_manager;
      }
      const Manager *
      manager() const
      {
        return m_manager;
      }

      absl::optional< absl::Duration >
      find(string_view categoryName) const
      {
        return find(m_manager->registry().get(categoryName));
      }

      absl::optional< absl::Duration >
      find(const Category *category) const;

      absl::optional< absl::Duration >
      getDefault() const;

      std::vector< std::pair< const Category *, absl::Duration > >
      getAll() const;
    };

  }  // namespace metrics
}  // namespace llarp

#endif