Flush reporters' output streams after writing a benchmark run (#288)

If a reporter's output stream isn't line-buffered (e.g. it's not writing to a terminal) then it can be some time before a write to it becomes visible. This is problematic if, say, you're wanting to use tail -f to view the file written to via --benchmark_out. Or if the application crashes, leaving you with no results. Addressed by flushing the reporters' output streams whenever we invoke methods that may write to them.

Flush reporters' output streams after writing a benchmark run (#288)
b826143a · Nicholas Hutchinson · Eric · c6f3f0eb · b826143a
Commit b826143a authored Sep 11, 2016 by Nicholas Hutchinson Committed by Eric Sep 11, 2016
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benchmark.cc src/benchmark.cc +14 -0

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--- a/src/benchmark.cc
+++ b/src/benchmark.cc
@@ -480,17 +480,31 @@ void RunMatchingBenchmarks(const std::vector<Benchmark::Instance>& benchmarks,
  // Keep track of runing times of all instances of current benchmark
  std::vector<BenchmarkReporter::Run> complexity_reports;
+  // We flush streams after invoking reporter methods that write to them. This
+  // ensures users get timely updates even when streams are not line-buffered.
+  auto flushStreams = [](BenchmarkReporter* reporter) {
+    if (!reporter) return;
+    std::flush(reporter->GetOutputStream());
+    std::flush(reporter->GetErrorStream());
+  };
  if (console_reporter->ReportContext(context)
      && (!file_reporter || file_reporter->ReportContext(context))) {
+    flushStreams(console_reporter);
+    flushStreams(file_reporter);
    for (const auto& benchmark : benchmarks) {
      std::vector<BenchmarkReporter::Run> reports =
          RunBenchmark(benchmark, &complexity_reports);
      console_reporter->ReportRuns(reports);
      if (file_reporter) file_reporter->ReportRuns(reports);
+      flushStreams(console_reporter);
+      flushStreams(file_reporter);
    }
  }
  console_reporter->Finalize();
  if (file_reporter) file_reporter->Finalize();
+  flushStreams(console_reporter);
+  flushStreams(file_reporter);
 }
 std::unique_ptr<BenchmarkReporter>