nanobench: flush after recording every Nth data point.

Got to keep our precious data in event of a crash.

With --flushEvery 10 I'm not seeing this cost any wall time.

BUG=skia:

Review URL: https://codereview.chromium.org/653083003

2 files changed, 16 insertions, 3 deletions

diff --git a/bench/ResultsWriter.h b/bench/ResultsWriter.h
index f17bce3d93..b8d97075a1 100644
--- a/bench/ResultsWriter.h
+++ b/bench/ResultsWriter.h
@@ -45,6 +45,9 @@ public:
 
     // Record a single test metric.
     virtual void timer(const char name[], double ms) {}
+
+    // Flush to storage now please.
+    virtual void flush() {}
 };
 
 /**
@@ -79,9 +82,7 @@ public:
         , fConfig(NULL) {}
 
     ~NanoJSONResultsWriter() {
-        SkFILEWStream stream(fFilename.c_str());
-        stream.writeText(Json::StyledWriter().write(fRoot).c_str());
-        stream.flush();
+        this->flush();
     }
 
     // Added under "key".
@@ -113,6 +114,13 @@ public:
         (*fConfig)[name] = ms;
     }
 
+    // Flush to storage now please.
+    virtual void flush() {
+        SkFILEWStream stream(fFilename.c_str());
+        stream.writeText(Json::StyledWriter().write(fRoot).c_str());
+        stream.flush();
+    }
+
 private:
     SkString fFilename;
     Json::Value fRoot;
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index d06d75358d..250f438d6a 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -70,6 +70,7 @@ DEFINE_int32(maxLoops, 1000000, "Never run a bench more times than this.");
 DEFINE_string(clip, "0,0,1000,1000", "Clip for SKPs.");
 DEFINE_string(scales, "1.0", "Space-separated scales for SKPs.");
 DEFINE_bool(bbh, true, "Build a BBH for SKPs?");
+DEFINE_int32(flushEvery, 10, "Flush --outResultsFile every Nth run.");
 
 static SkString humanize(double ms) {
     if (FLAGS_verbose) return SkStringPrintf("%llu", (uint64_t)(ms*1e6));
@@ -628,6 +629,7 @@ int nanobench_main() {
     SkTDArray<Config> configs;
     create_configs(&configs);
 
+    int runs = 0;
     BenchmarkStream benchStream;
     while (Benchmark* b = benchStream.next()) {
         SkAutoTDelete<Benchmark> bench(b);
@@ -680,6 +682,9 @@ int nanobench_main() {
             log->timer("mean_ms",   stats.mean);
             log->timer("max_ms",    stats.max);
             log->timer("stddev_ms", sqrt(stats.var));
+            if (runs++ % FLAGS_flushEvery == 0) {
+                log->flush();
+            }
 
             if (kAutoTuneLoops != FLAGS_loops) {
                 if (targets.count() == 1) {