Support sampling histograms

conanfile.py

@@ -5,7 +5,7 @@
 
 class CxxmetricsConan(ConanFile):
     name = "cxxmetrics"
-    version = "0.0.7"
+    version = "0.0.8"
     license = "Apache 2.0"
     settings = "os"
     url = "https://github.com/kmaragon/cxxmetrics"

cxxmetrics/ewma.hpp

@@ -216,7 +216,7 @@ TValue ewma<TClockGet, TWindow, TInterval, TValue>::tick(const clock_point &at)
     if (missed_intervals > 0)
     {
         // we missed some intervals - we'll average in zeros
-        if ((at - last) > period(TWindow) && TWindow > TInterval)
+        if ((TWindow > TInterval) && (at - last) > period(TWindow))
         {
             constexpr auto intervals_per_window = TWindow / TInterval;
             period::value missed_windows = missed_intervals / intervals_per_window;

cxxmetrics/metric_value.hpp

@@ -863,9 +863,9 @@ class metric_value
     }
 
     template<typename TRep, typename TPer>
-    operator std::chrono::nanoseconds() const
+    operator std::chrono::duration<TRep, TPer>() const
     {
-        return value_.to_nanos();
+        return std::chrono::duration_cast<std::chrono::duration<TRep, TPer>>(value_.to_nanos());
     }
 };
 

cxxmetrics/snapshots.hpp

@@ -289,6 +289,50 @@ class reservoir_snapshot
         return values_[index - 1] + metric_value((pos - index) * static_cast<long double>(values_[index] - values_[index - 1]));
     }
 
+    /**
+     * \brief Sample n values from the snapshot, calling a function for each
+     * sampled value
+     *
+     * \tparam Handler The handler type
+     *
+     * The handler will receive a const metric_value and quantile
+     *
+     * \param max_to_visit The maximum number of values
+     * \param hnd The handler to call for each metric_value in the snapshot
+     */
+    template <typename Handler>
+    void sample(std::size_t max_to_visit, Handler hnd) const
+    {
+        long double q_proportion = 1.0L / std::min(
+            static_cast<long double>(max_to_visit + 1),
+            static_cast<long double>(values_.size() - 1));
+
+        for (std::size_t i = 0; i < max_to_visit; i++) {
+            long double q = q_proportion * (i + 1);
+
+            auto pos = q * (values_.size() + 1);
+            auto index = static_cast<std::size_t>(pos);
+            if (index >= values_.size())
+                return;
+
+            if (index < 1) {
+                hnd(min(), pos * 100 / static_cast<long double>(values_.size() + 1));
+                continue;
+            }
+
+            if (index >= values_.size()) {
+                hnd(max(), pos * 100 / static_cast<long double>(values_.size() + 1));
+                continue;
+            }
+
+            hnd(values_[index - 1] +
+                    metric_value(
+                        (pos - static_cast<double>(index)) *
+                        static_cast<long double>(values_[index] - values_[index - 1])),
+                pos * 100 / static_cast<long double>(values_.size() + 1));
+        }
+    }
+
     /**
      * \brief Get the mean value in the snapshot
      *

test/conanfile.py

@@ -6,7 +6,7 @@ class CxxmetricsTestConan(ConanFile):
     settings = "os", "compiler", "build_type", "arch"
     generators = "cmake"
     exports = "CMakeLists.txt", "../test*"
-    build_requires = "catch2/2.3.0@bincrafters/stable"
+    build_requires = "catch2/2.13.9"
 
     def source(self):
         tools.replace_in_file("CMakeLists.txt", "project(\"cxxmetrics_test\" CXX)", '''project("cxxmetrics_test" CXX)

test/publisher_tests.cpp

@@ -326,6 +326,10 @@ TEST_CASE("Publisher can get histogram options", "[publisher]")
             {
                 values.emplace(q, round(v));
             });
+
+            ss.sample(9, [&](const metric_value& v, quantile q) {
+                values.emplace(q, round(v));
+            });
         });
     };
 
@@ -337,7 +341,7 @@ TEST_CASE("Publisher can get histogram options", "[publisher]")
 
     subject.visit_registry(visitor);
     REQUIRE(value == metric_value(50));
-    REQUIRE(values.size() == 3); // defaults
+    REQUIRE(values.size() == 12); // defaults
     REQUIRE(count == 2);
 
     print_percentiles(values);
@@ -348,6 +352,6 @@ TEST_CASE("Publisher can get histogram options", "[publisher]")
 
     print_percentiles(values);
     REQUIRE(value == metric_value(0));
-    REQUIRE(values.size() == 1);
+    REQUIRE(values.size() == 10);
     REQUIRE(count == 4);
 }

test/reservoir_test.cpp

@@ -99,7 +99,7 @@ TEST_CASE("Simple Reservoir threaded updates with snapshots", "[reservoir]")
     for (int i = 0; i < 1000; i++)
     {
         auto s = r.snapshot();
-        CAPTURE(i)
+        CAPTURE(i);
         REQUIRE(s.size() >= minsize);
     }