Add ClearRegisteredBenchmark() function. (#402)

* Add ClearRegisteredBenchmark() function.

Since benchmarks can be registered at runtime using the RegisterBenchmark(...)
functions, it makes sense to have a ClearRegisteredBenchmarks() function too,
that can be used at runtime to clear the currently registered benchmark and
re-register an entirely new set.

This allows users to run a set of registered benchmarks, get the output using
a custom reporter, and then clear and re-register new benchmarks based on the
previous results.

This fixes issue #400, at least partially.

* Remove unused change

include/benchmark/benchmark_api.h

@@ -707,6 +707,10 @@ template <class Lambda>
 internal::Benchmark* RegisterBenchmark(const char* name, Lambda&& fn);
 #endif
 
+// Remove all registered benchmarks. All pointers to previously registered
+// benchmarks are invalidated.
+void ClearRegisteredBenchmarks();
+
 namespace internal {
 // The class used to hold all Benchmarks created from static function.
 // (ie those created using the BENCHMARK(...) macros.

src/benchmark_register.cc

@@ -70,6 +70,9 @@ class BenchmarkFamilies {
   // Registers a benchmark family and returns the index assigned to it.
   size_t AddBenchmark(std::unique_ptr<Benchmark> family);
 
+  // Clear all registered benchmark families.
+  void ClearBenchmarks();
+
   // Extract the list of benchmark instances that match the specified
   // regular expression.
   bool FindBenchmarks(const std::string& re,
@@ -95,6 +98,12 @@ size_t BenchmarkFamilies::AddBenchmark(std::unique_ptr<Benchmark> family) {
   return index;
 }
 
+void BenchmarkFamilies::ClearBenchmarks() {
+  MutexLock l(mutex_);
+  families_.clear();
+  families_.shrink_to_fit();
+}
+
 bool BenchmarkFamilies::FindBenchmarks(
     const std::string& spec, std::vector<Benchmark::Instance>* benchmarks,
     std::ostream* ErrStream) {
@@ -450,4 +459,9 @@ int Benchmark::ArgsCnt() const {
 void FunctionBenchmark::Run(State& st) { func_(st); }
 
 }  // end namespace internal
+
+void ClearRegisteredBenchmarks() {
+  internal::BenchmarkFamilies::GetInstance()->ClearBenchmarks();
+}
+
 }  // end namespace benchmark

test/register_benchmark_test.cc

@@ -126,11 +126,11 @@ void TestRegistrationAtRuntime() {
 #endif
 }
 
-int main(int argc, char* argv[]) {
+// Test that all benchmarks, registered at either during static init or runtime,
+// are run and the results are passed to the reported.
+void RunTestOne() {
   TestRegistrationAtRuntime();
 
-  benchmark::Initialize(&argc, argv);
-
   TestReporter test_reporter;
   benchmark::RunSpecifiedBenchmarks(&test_reporter);
 
@@ -143,6 +143,40 @@ int main(int argc, char* argv[]) {
     ++EB;
   }
   assert(EB == ExpectedResults.end());
-
+}
-  return 0;
+
+// Test that ClearRegisteredBenchmarks() clears all previously registered
+// benchmarks.
+// Also test that new benchmarks can be registered and ran afterwards.
+void RunTestTwo() {
+  assert(ExpectedResults.size() != 0 &&
+         "must have at least one registered benchmark");
+  ExpectedResults.clear();
+  benchmark::ClearRegisteredBenchmarks();
+
+  TestReporter test_reporter;
+  size_t num_ran = benchmark::RunSpecifiedBenchmarks(&test_reporter);
+  assert(num_ran == 0);
+  assert(test_reporter.all_runs_.begin() == test_reporter.all_runs_.end());
+
+  TestRegistrationAtRuntime();
+  num_ran = benchmark::RunSpecifiedBenchmarks(&test_reporter);
+  assert(num_ran == ExpectedResults.size());
+
+  typedef benchmark::BenchmarkReporter::Run Run;
+  auto EB = ExpectedResults.begin();
+
+  for (Run const& run : test_reporter.all_runs_) {
+    assert(EB != ExpectedResults.end());
+    EB->CheckRun(run);
+    ++EB;
+  }
+  assert(EB == ExpectedResults.end());
+}
+
+int main(int argc, char* argv[]) {
+  benchmark::Initialize(&argc, argv);
+
+  RunTestOne();
+  RunTestTwo();
 }