Add utility for creating vector access histograms

include/util/timed_histogram.hpp

@@ -0,0 +1,94 @@
+#ifndef OSRM_UTIL_TIMED_HISTOGRAM_HPP
+#define OSRM_UTIL_TIMED_HISTOGRAM_HPP
+
+#include "util/integer_range.hpp"
+
+#include <algorithm>
+#include <atomic>
+#include <mutex>
+#include <sstream>
+#include <vector>
+
+namespace osrm
+{
+namespace util
+{
+namespace detail
+{
+extern std::atomic_uint operation;
+}
+
+/**
+ * Captures a histogram with a bin size of `IndexBinSize` every `TimeBinSize` count operations.
+ */
+template <std::size_t TimeBinSize = 1000, std::size_t IndexBinSize = 1000> class TimedHistogram
+{
+  public:
+    void Count(std::size_t pos)
+    {
+        std::lock_guard<std::mutex> guard(frames_lock);
+        auto frame_index = detail::operation++ / TimeBinSize;
+
+        while (frame_offsets.size() <= frame_index)
+        {
+            frame_offsets.push_back(frame_counters.size());
+        }
+        BOOST_ASSERT(frame_offsets.size() == frame_index+1);
+
+        auto frame_offset = frame_offsets.back();
+        auto counter_index = frame_offset + pos / IndexBinSize;
+
+        while (counter_index >= frame_counters.size())
+        {
+            frame_counters.push_back(0);
+        }
+
+        BOOST_ASSERT(frame_counters.size() > counter_index);
+        frame_counters[counter_index]++;
+    }
+
+    // Returns the measurments as a CSV file with the columns:
+    // frame_id,index_bin,count
+    std::string DumpCSV() const
+    {
+        std::stringstream out;
+
+        const auto print_bins = [&out](auto frame_index, auto begin, auto end) {
+            auto bin_index = 0;
+            std::for_each(begin, end, [&](const auto count) {
+                if (count > 0)
+                {
+                    out << (frame_index * TimeBinSize) << "," << (bin_index * IndexBinSize) << ","
+                        << count << std::endl;
+                }
+                bin_index++;
+            });
+        };
+
+        if (frame_offsets.size() == 0)
+        {
+            return "";
+        }
+
+        for (const auto frame_index : irange<std::size_t>(0, frame_offsets.size() - 1))
+        {
+            auto begin = frame_counters.begin() + frame_offsets[frame_index];
+            auto end = frame_counters.begin() + frame_offsets[frame_index + 1];
+            print_bins(frame_index, begin, end);
+        }
+        print_bins(frame_offsets.size() - 1,
+                   frame_counters.begin() + frame_offsets.back(),
+                   frame_counters.end());
+
+        return out.str();
+    }
+
+  private:
+    std::mutex frames_lock;
+    std::vector<std::uint32_t> frame_offsets;
+    std::vector<std::uint32_t> frame_counters;
+};
+}
+}
+
+#endif

src/util/timed_historgram.cpp

@@ -0,0 +1,12 @@
+#include "util/timed_histogram.hpp"
+
+namespace osrm
+{
+namespace util
+{
+namespace detail
+{
+std::atomic_uint operation = {0};
+}
+}
+}