Benchmark json_document

benchmarks_view.cpp adds ViewParse, ViewRead (a reused document),
ViewParseIndented, ViewAccept, and ViewMaterialize on the files of
ParseString, so that each row can be read against the json::parse row of
the same file; benchmarks.cpp gains Accept (json::accept) as the
counterpart of ViewAccept. The view benchmarks are built only if the
header directory has json_view.hpp, so that older versions can still be
benchmarked.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/benchmarks/src/benchmarks_view.cpp

@@ -0,0 +1,146 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+// Benchmarks of json_document (nlohmann/json_view.hpp). They use the inputs of
+// ParseString and ParseIndented in benchmarks.cpp, so that each ViewParse row
+// can be read against the json::parse row of the same file.
+
+#include <benchmark/benchmark.h>
+#include <nlohmann/json_view.hpp>
+#include <fstream>
+#include <iterator>
+#include <string>
+#include <test_data.hpp>
+
+using json = nlohmann::json;
+using json_document = nlohmann::json_document;
+
+static std::string read_file(const char* filename)
+{
+    std::ifstream f(filename, std::ios::binary);
+    return std::string((std::istreambuf_iterator<char>(f)), std::istreambuf_iterator<char>());
+}
+
+#define JSON_VIEW_BENCHMARK_FILES(fn) \
+    BENCHMARK_CAPTURE(fn, jeopardy,          TEST_DATA_DIRECTORY "/jeopardy/jeopardy.json"); \
+    BENCHMARK_CAPTURE(fn, canada,            TEST_DATA_DIRECTORY "/nativejson-benchmark/canada.json"); \
+    BENCHMARK_CAPTURE(fn, citm_catalog,      TEST_DATA_DIRECTORY "/nativejson-benchmark/citm_catalog.json"); \
+    BENCHMARK_CAPTURE(fn, twitter,           TEST_DATA_DIRECTORY "/nativejson-benchmark/twitter.json"); \
+    BENCHMARK_CAPTURE(fn, floats,            TEST_DATA_DIRECTORY "/regression/floats.json"); \
+    BENCHMARK_CAPTURE(fn, signed_ints,       TEST_DATA_DIRECTORY "/regression/signed_ints.json"); \
+    BENCHMARK_CAPTURE(fn, unsigned_ints,     TEST_DATA_DIRECTORY "/regression/unsigned_ints.json"); \
+    BENCHMARK_CAPTURE(fn, small_signed_ints, TEST_DATA_DIRECTORY "/regression/small_signed_ints.json")
+
+//////////////////////////////////////////////////////////////////////////////
+// parse into a new document (compare with ParseString)
+//////////////////////////////////////////////////////////////////////////////
+
+static void ViewParse(benchmark::State& state, const char* filename)
+{
+    const std::string str = read_file(filename);
+
+    while (state.KeepRunning())
+    {
+        state.PauseTiming();
+        auto* d = new json_document();
+        state.ResumeTiming();
+
+        *d = json_document::parse(str);
+
+        state.PauseTiming();
+        delete d;
+        state.ResumeTiming();
+    }
+
+    state.SetBytesProcessed(state.iterations() * str.size());
+}
+JSON_VIEW_BENCHMARK_FILES(ViewParse);
+
+//////////////////////////////////////////////////////////////////////////////
+// parse into a document that is reused (its memory stays allocated)
+//////////////////////////////////////////////////////////////////////////////
+
+static void ViewRead(benchmark::State& state, const char* filename)
+{
+    const std::string str = read_file(filename);
+    json_document d;
+
+    while (state.KeepRunning())
+    {
+        d.read(str);
+        benchmark::DoNotOptimize(d);
+    }
+
+    state.SetBytesProcessed(state.iterations() * str.size());
+}
+JSON_VIEW_BENCHMARK_FILES(ViewRead);
+
+//////////////////////////////////////////////////////////////////////////////
+// parse pretty-printed JSON (compare with ParseIndented)
+//////////////////////////////////////////////////////////////////////////////
+
+static void ViewParseIndented(benchmark::State& state, const char* filename, int indent)
+{
+    const std::string indented = json::parse(read_file(filename)).dump(indent);
+    json_document d;
+
+    while (state.KeepRunning())
+    {
+        d.read(indented);
+        benchmark::DoNotOptimize(d);
+    }
+
+    state.SetBytesProcessed(state.iterations() * indented.size());
+}
+BENCHMARK_CAPTURE(ViewParseIndented, jeopardy / 4,     TEST_DATA_DIRECTORY "/jeopardy/jeopardy.json",                 4);
+BENCHMARK_CAPTURE(ViewParseIndented, canada / 4,       TEST_DATA_DIRECTORY "/nativejson-benchmark/canada.json",       4);
+BENCHMARK_CAPTURE(ViewParseIndented, citm_catalog / 4, TEST_DATA_DIRECTORY "/nativejson-benchmark/citm_catalog.json", 4);
+BENCHMARK_CAPTURE(ViewParseIndented, twitter / 4,      TEST_DATA_DIRECTORY "/nativejson-benchmark/twitter.json",      4);
+
+//////////////////////////////////////////////////////////////////////////////
+// validate only (compare with Accept)
+//////////////////////////////////////////////////////////////////////////////
+
+static void ViewAccept(benchmark::State& state, const char* filename)
+{
+    const std::string str = read_file(filename);
+
+    while (state.KeepRunning())
+    {
+        benchmark::DoNotOptimize(json_document::accept(str));
+    }
+
+    state.SetBytesProcessed(state.iterations() * str.size());
+}
+JSON_VIEW_BENCHMARK_FILES(ViewAccept);
+
+//////////////////////////////////////////////////////////////////////////////
+// convert a parsed document into a json value
+//////////////////////////////////////////////////////////////////////////////
+
+static void ViewMaterialize(benchmark::State& state, const char* filename)
+{
+    const std::string str = read_file(filename);
+    const json_document d = json_document::parse(str);
+
+    while (state.KeepRunning())
+    {
+        state.PauseTiming();
+        auto* j = new json();
+        state.ResumeTiming();
+
+        *j = d.root().materialize();
+
+        state.PauseTiming();
+        delete j;
+        state.ResumeTiming();
+    }
+
+    state.SetBytesProcessed(state.iterations() * str.size());
+}
+JSON_VIEW_BENCHMARK_FILES(ViewMaterialize);