Print benchmark results as they complete

Summary:
Print benchmark results as and when they complete instead of outputting the
whole thing once at the end

Reviewed By: djwatson, ot

Differential Revision: D9177038

fbshipit-source-id: 54898b303771f214c21163cd87b11f8e2083cdf4

folly/Benchmark.cpp

@@ -244,33 +244,25 @@ static string metricReadable(double n, unsigned int decimals) {
   return humanReadable(n, decimals, kMetricSuffixes);
 }
 
-static void printBenchmarkResultsAsTable(
-    const vector<detail::BenchmarkResult>& data) {
-  // Width available
-  static const unsigned int columns = 76;
-
-  // Compute the longest benchmark name
-  size_t longestName = 0;
-  for (auto& bm : benchmarks()) {
-    longestName = max(longestName, bm.name.size());
-  }
+namespace {
+class BenchmarkResultsPrinter {
+ public:
+  static constexpr unsigned int columns{76};
+  double baselineNsPerIter{numeric_limits<double>::max()};
+  string lastFile;
 
-  // Print a horizontal rule
-  auto separator = [&](char pad) {
+  void separator(char pad) {
     puts(string(columns, pad).c_str());
-  };
+  }
 
-  // Print header for a file
-  auto header = [&](const string& file) {
+  void header(const string& file) {
     separator('=');
     printf("%-*srelative  time/iter  iters/s\n",
            columns - 28, file.c_str());
     separator('=');
-  };
-
-  double baselineNsPerIter = numeric_limits<double>::max();
-  string lastFile;
+  }
 
+  void print(const vector<detail::BenchmarkResult>& data) {
     for (auto& datum : data) {
       auto file = datum.file;
       if (file != lastFile) {
@@ -300,22 +292,27 @@ static void printBenchmarkResultsAsTable(
           : (1 / secPerIter);
       if (!useBaseline) {
         // Print without baseline
-      printf("%*s           %9s  %7s\n",
-             static_cast<int>(s.size()), s.c_str(),
+        printf(
+            "%*s           %9s  %7s\n",
+            static_cast<int>(s.size()),
+            s.c_str(),
             readableTime(secPerIter, 2).c_str(),
             metricReadable(itersPerSec, 2).c_str());
       } else {
         // Print with baseline
         auto rel = baselineNsPerIter / nsPerIter * 100.0;
-      printf("%*s %7.2f%%  %9s  %7s\n",
-             static_cast<int>(s.size()), s.c_str(),
+        printf(
+            "%*s %7.2f%%  %9s  %7s\n",
+            static_cast<int>(s.size()),
+            s.c_str(),
             rel,
             readableTime(secPerIter, 2).c_str(),
             metricReadable(itersPerSec, 2).c_str());
       }
     }
-  separator('=');
-}
+  }
+};
+} // namespace
 
 static void printBenchmarkResultsAsJson(
     const vector<detail::BenchmarkResult>& data) {
@@ -337,11 +334,13 @@ static void printBenchmarkResultsAsVerboseJson(
 static void printBenchmarkResults(const vector<detail::BenchmarkResult>& data) {
   if (FLAGS_json_verbose) {
     printBenchmarkResultsAsVerboseJson(data);
+    return;
   } else if (FLAGS_json) {
     printBenchmarkResultsAsJson(data);
-  } else {
-    printBenchmarkResultsAsTable(data);
+    return;
   }
+
+  CHECK(FLAGS_json_verbose || FLAGS_json) << "Cannot print benchmark results";
 }
 
 void benchmarkResultsToDynamic(
@@ -461,6 +460,7 @@ void runBenchmarks() {
 
   auto const globalBaseline =
       runBenchmarkGetNSPerIteration(benchmarks()[baselineIndex].func, 0);
+  auto printer = BenchmarkResultsPrinter{};
   FOR_EACH_RANGE (i, 0, benchmarks().size()) {
     if (i == baselineIndex) {
       continue;
@@ -473,12 +473,21 @@ void runBenchmarks() {
       }
       elapsed = runBenchmarkGetNSPerIteration(bm.func, globalBaseline);
     }
+
+    if (!FLAGS_json_verbose && !FLAGS_json) {
+      printer.print({{bm.file, bm.name, elapsed}});
+    } else {
       results.push_back({bm.file, bm.name, elapsed});
     }
+  }
 
   // PLEASE MAKE NOISE. MEASUREMENTS DONE.
 
+  if (FLAGS_json_verbose || FLAGS_json) {
     printBenchmarkResults(results);
+  } else {
+    printer.separator('=');
+  }
 }
 
 } // namespace folly