Cache PerfCounters instance in PerfCountersMeasurement (#1308)

This patch fixes #1306, by reducing the pinned instances of
PerfCounters.

The issue is caused by creating multiple pinned events in the
same thread, doing so results in the Snapshot(PerfCounterValues* values)
failing, and that's now discoverable.
Creating multile pinned events is an unsupported behavior currently.
The error would be detected at read() time, not
perf_event_open() / iotcl() time.

The unsupported benavior above is confirmed by Stephane Eranian @seranian,
and he also pointed the dectection method.

Finished this patch under the guidance of Mircea Trofin @mtrofin.

1 files changed, 48 insertions, 0 deletions

diff --git a/test/perf_counters_gtest.cc b/test/perf_counters_gtest.cc
index 3eac624..f9e6a6f 100644
--- a/test/perf_counters_gtest.cc
+++ b/test/perf_counters_gtest.cc
@@ -11,6 +11,7 @@ struct MsgHandler {
 #endif
 
 using benchmark::internal::PerfCounters;
+using benchmark::internal::PerfCountersMeasurement;
 using benchmark::internal::PerfCounterValues;
 
 namespace {
@@ -95,6 +96,53 @@ TEST(PerfCountersTest, Read2Counters) {
   EXPECT_GT(values2[1], 0);
 }
 
+TEST(PerfCountersTest, ReopenExistingCounters) {
+  // The test works (i.e. causes read to fail) for the assumptions
+  // about hardware capabilities (i.e. small number (3-4) hardware
+  // counters) at this date.
+  if (!PerfCounters::kSupported) {
+    GTEST_SKIP() << "Test skipped because libpfm is not supported.\n";
+  }
+  EXPECT_TRUE(PerfCounters::Initialize());
+  std::vector<PerfCounters> counters;
+  counters.reserve(6);
+  for (int i = 0; i < 6; i++)
+    counters.push_back(PerfCounters::Create({kGenericPerfEvent1}));
+  PerfCounterValues values(1);
+  EXPECT_TRUE(counters[0].Snapshot(&values));
+  EXPECT_FALSE(counters[4].Snapshot(&values));
+  EXPECT_FALSE(counters[5].Snapshot(&values));
+}
+
+TEST(PerfCountersTest, CreateExistingMeasurements) {
+  // The test works (i.e. causes read to fail) for the assumptions
+  // about hardware capabilities (i.e. small number (3-4) hardware
+  // counters) at this date,
+  // the same as previous test ReopenExistingCounters.
+  if (!PerfCounters::kSupported) {
+    GTEST_SKIP() << "Test skipped because libpfm is not supported.\n";
+  }
+  EXPECT_TRUE(PerfCounters::Initialize());
+  std::vector<PerfCountersMeasurement> perf_counter_measurements;
+  std::vector<std::pair<std::string, double>> measurements;
+
+  perf_counter_measurements.reserve(10);
+  for (int i = 0; i < 10; i++)
+    perf_counter_measurements.emplace_back(
+        std::vector<std::string>{kGenericPerfEvent1});
+
+  perf_counter_measurements[0].Start();
+  EXPECT_TRUE(perf_counter_measurements[0].Stop(measurements));
+
+  measurements.clear();
+  perf_counter_measurements[8].Start();
+  EXPECT_FALSE(perf_counter_measurements[8].Stop(measurements));
+
+  measurements.clear();
+  perf_counter_measurements[9].Start();
+  EXPECT_FALSE(perf_counter_measurements[9].Stop(measurements));
+}
+
 size_t do_work() {
   size_t res = 0;
   for (size_t i = 0; i < 100000000; ++i) res += i * i;