Add API to benchmark allowing for custom context to be added (#1137)

README.md

@@ -463,6 +463,15 @@ BM_memcpy/32          11 ns         11 ns   79545455
 BM_memcpy/32k       2181 ns       2185 ns     324074
 ```
 
+You can get the same effect with the API:
+
+```c++
+  benchmark::AddCustomContext("foo", "bar");
+```
+
+Note that attempts to add a second value with the same key will fail with an
+error message.
+
 <a name="runtime-and-reporting-considerations" />
 
 ### Runtime and Reporting Considerations

include/benchmark/benchmark.h

@@ -294,6 +294,9 @@ size_t RunSpecifiedBenchmarks(BenchmarkReporter* display_reporter,
 // allocation measurements for benchmark runs.
 void RegisterMemoryManager(MemoryManager* memory_manager);
 
+// Add a key-value pair to output as part of the context stanza in the report.
+void AddCustomContext(const std::string& key, const std::string& value);
+
 namespace internal {
 class Benchmark;
 class BenchmarkImp;

src/benchmark.cc

@@ -33,6 +33,7 @@
 #include <cstdlib>
 #include <fstream>
 #include <iostream>
+#include <map>
 #include <memory>
 #include <string>
 #include <thread>
@@ -105,10 +106,6 @@ DEFINE_string(benchmark_color, "auto");
 // Valid values: 'true'/'yes'/1, 'false'/'no'/0.  Defaults to false.
 DEFINE_bool(benchmark_counters_tabular, false);
 
-// Extra context to include in the output formatted as comma-separated key-value
-// pairs.
-DEFINE_kvpairs(benchmark_context, {});
-
 // The level of verbose logging to output
 DEFINE_int32(v, 0);
 
@@ -117,9 +114,14 @@ DEFINE_int32(v, 0);
 DEFINE_string(benchmark_perf_counters, "");
 
 namespace benchmark {
-
 namespace internal {
 
+// Extra context to include in the output formatted as comma-separated key-value
+// pairs. Kept internal as it's only used for parsing from env/command line.
+DEFINE_kvpairs(benchmark_context, {});
+
+std::map<std::string, std::string>* global_context = nullptr;
+
 // FIXME: wouldn't LTO mess this up?
 void UseCharPointer(char const volatile*) {}
 
@@ -435,6 +437,16 @@ void RegisterMemoryManager(MemoryManager* manager) {
   internal::memory_manager = manager;
 }
 
+void AddCustomContext(const std::string& key, const std::string& value) {
+  if (internal::global_context == nullptr) {
+    internal::global_context = new std::map<std::string, std::string>();
+  }
+  if (!internal::global_context->emplace(key, value).second) {
+    std::cerr << "Failed to add custom context \"" << key << "\" as it already "
+              << "exists with value \"" << value << "\"\n";
+  }
+}
+
 namespace internal {
 
 void PrintUsageAndExit() {
@@ -496,13 +508,17 @@ void ParseCommandLineFlags(int* argc, char** argv) {
     }
   }
   for (auto const* flag :
-       {&FLAGS_benchmark_format, &FLAGS_benchmark_out_format})
+       {&FLAGS_benchmark_format, &FLAGS_benchmark_out_format}) {
     if (*flag != "console" && *flag != "json" && *flag != "csv") {
       PrintUsageAndExit();
     }
+  }
   if (FLAGS_benchmark_color.empty()) {
     PrintUsageAndExit();
   }
+  for (const auto& kv : FLAGS_benchmark_context) {
+    AddCustomContext(kv.first, kv.second);
+  }
 }
 
 int InitializeStreams() {

src/json_reporter.cc

@@ -29,6 +29,9 @@
 #include "timers.h"
 
 namespace benchmark {
+namespace internal {
+extern std::map<std::string, std::string>* global_context;
+}
 
 namespace {
 
@@ -160,6 +163,13 @@ bool JSONReporter::ReportContext(const Context& context) {
   const char build_type[] = "debug";
 #endif
   out << indent << FormatKV("library_build_type", build_type) << "\n";
+
+  if (internal::global_context != nullptr) {
+    for (const auto& kv: *internal::global_context) {
+      out << indent << FormatKV(kv.first, kv.second) << "\n";
+    }
+  }
+
   // Close context block and open the list of benchmarks.
   out << inner_indent << "},\n";
   out << inner_indent << "\"benchmarks\": [\n";

src/reporter.cc

@@ -18,16 +18,18 @@
 #include <cstdlib>
 
 #include <iostream>
+#include <map>
+#include <string>
 #include <tuple>
 #include <vector>
 
 #include "check.h"
-#include "commandlineflags.h"
 #include "string_util.h"
 
-DECLARE_kvpairs(benchmark_context);
-
 namespace benchmark {
+namespace internal {
+extern std::map<std::string, std::string>* global_context;
+}
 
 BenchmarkReporter::BenchmarkReporter()
     : output_stream_(&std::cout), error_stream_(&std::cerr) {}
@@ -67,8 +69,10 @@ void BenchmarkReporter::PrintBasicContext(std::ostream *out,
     Out << "\n";
   }
 
-  for (const auto& kv: FLAGS_benchmark_context) {
-    Out << kv.first << ": " << kv.second << "\n";
+  if (internal::global_context != nullptr) {
+    for (const auto& kv: *internal::global_context) {
+      Out << kv.first << ": " << kv.second << "\n";
+    }
   }
 
   if (CPUInfo::Scaling::ENABLED == info.scaling) {

test/benchmark_gtest.cc

+#include <map>
+#include <string>
 #include <vector>
 
 #include "../src/benchmark_register.h"
@@ -6,6 +8,8 @@
 
 namespace benchmark {
 namespace internal {
+extern std::map<std::string, std::string>* global_context;
+
 namespace {
 
 TEST(AddRangeTest, Simple) {
@@ -129,6 +133,31 @@ TEST(AddRangeTest, Simple8) {
   EXPECT_THAT(dst, testing::ElementsAre(1, 2, 4, 8));
 }
 
+TEST(AddCustomContext, Simple) {
+  EXPECT_THAT(global_context, nullptr);
+
+  AddCustomContext("foo", "bar");
+  AddCustomContext("baz", "qux");
+
+  EXPECT_THAT(*global_context,
+              testing::UnorderedElementsAre(testing::Pair("foo", "bar"),
+                                            testing::Pair("baz", "qux")));
+
+  global_context = nullptr;
+}
+
+TEST(AddCustomContext, DuplicateKey) {
+  EXPECT_THAT(global_context, nullptr);
+
+  AddCustomContext("foo", "bar");
+  AddCustomContext("foo", "qux");
+
+  EXPECT_THAT(*global_context,
+              testing::UnorderedElementsAre(testing::Pair("foo", "bar")));
+
+  global_context = nullptr;
+}
+
 }  // namespace
 }  // namespace internal
 }  // namespace benchmark