git.sesse.net Git - nageru/blob - metrics.h

   1 #ifndef _METRICS_H
   2 #define _METRICS_H 1
   3
   4 // A simple global class to keep track of metrics export in Prometheus format.
   5 // It would be better to use a more full-featured Prometheus client library for this,
   6 // but it would introduce a dependency that is not commonly packaged in distributions,
   7 // which makes it quite unwieldy. Thus, we'll package our own for the time being.
   8
   9 #include <atomic>
  10 #include <map>
  11 #include <memory>
  12 #include <mutex>
  13 #include <string>
  14 #include <vector>
  15
  16 class Histogram;
  17
  18 class Metrics {
  19 public:
  20         enum Type {
  21                 TYPE_COUNTER,
  22                 TYPE_GAUGE,
  23                 TYPE_HISTOGRAM,  // Internal use only.
  24         };
  25
  26         void add(const std::string &name, std::atomic<int64_t> *location, Type type = TYPE_COUNTER)
  27         {
  28                 add(name, {}, location, type);
  29         }
  30
  31         void add(const std::string &name, std::atomic<double> *location, Type type = TYPE_COUNTER)
  32         {
  33                 add(name, {}, location, type);
  34         }
  35
  36         void add(const std::string &name, Histogram *location)
  37         {
  38                 add(name, {}, location);
  39         }
  40
  41         void add(const std::string &name, const std::vector<std::pair<std::string, std::string>> &labels, std::atomic<int64_t> *location, Type type = TYPE_COUNTER);
  42         void add(const std::string &name, const std::vector<std::pair<std::string, std::string>> &labels, std::atomic<double> *location, Type type = TYPE_COUNTER);
  43         void add(const std::string &name, const std::vector<std::pair<std::string, std::string>> &labels, Histogram *location);
  44
  45         std::string serialize() const;
  46
  47 private:
  48         enum DataType {
  49                 DATA_TYPE_INT64,
  50                 DATA_TYPE_DOUBLE,
  51                 DATA_TYPE_HISTOGRAM,
  52         };
  53
  54         struct Metric {
  55                 DataType data_type;
  56                 std::string name;
  57                 std::vector<std::pair<std::string, std::string>> labels;
  58                 union {
  59                         std::atomic<int64_t> *location_int64;
  60                         std::atomic<double> *location_double;
  61                         Histogram *location_histogram;
  62                 };
  63         };
  64
  65         mutable std::mutex mu;
  66         std::map<std::string, Type> types;
  67         std::vector<Metric> metrics;
  68         std::vector<Histogram> histograms;
  69 };
  70
  71 class Histogram {
  72 public:
  73         void init(const std::vector<double> &bucket_vals);
  74         void init_uniform(size_t num_buckets);  // Sets up buckets 0..(N-1).
  75         void count_event(double val);
  76         std::string serialize(const std::string &name, const std::vector<std::pair<std::string, std::string>> &labels) const;
  77
  78 private:
  79         // Bucket <i> counts number of events where val[i - 1] < x <= val[i].
  80         // The end histogram ends up being made into a cumulative one,
  81         // but that's not how we store it here.
  82         struct Bucket {
  83                 double val;
  84                 std::atomic<int64_t> count{0};
  85         };
  86         std::unique_ptr<Bucket[]> buckets;
  87         size_t num_buckets;
  88         std::atomic<double> sum{0.0};
  89         std::atomic<int64_t> count_after_last_bucket{0};
  90 };
  91
  92 extern Metrics global_metrics;
  93
  94 #endif  // !defined(_METRICS_H)