diff --git a/src/benchmark_runner.cc b/src/benchmark_runner.cc
new file mode 100644
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--- /dev/null
+++ b/src/benchmark_runner.cc
@@ -0,0 +1,350 @@
+// Copyright 2015 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "benchmark_runner.h"
+#include "benchmark/benchmark.h"
+#include "benchmark_api_internal.h"
+#include "internal_macros.h"
+
+#ifndef BENCHMARK_OS_WINDOWS
+#ifndef BENCHMARK_OS_FUCHSIA
+#include <sys/resource.h>
+#endif
+#include <sys/time.h>
+#include <unistd.h>
+#endif
+
+#include <algorithm>
+#include <atomic>
+#include <condition_variable>
+#include <cstdio>
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+#include <memory>
+#include <string>
+#include <thread>
+#include <utility>
+
+#include "check.h"
+#include "colorprint.h"
+#include "commandlineflags.h"
+#include "complexity.h"
+#include "counter.h"
+#include "internal_macros.h"
+#include "log.h"
+#include "mutex.h"
+#include "re.h"
+#include "statistics.h"
+#include "string_util.h"
+#include "thread_manager.h"
+#include "thread_timer.h"
+
+namespace benchmark {
+
+namespace internal {
+
+MemoryManager* memory_manager = nullptr;
+
+namespace {
+
+static const size_t kMaxIterations = 1000000000;
+
+BenchmarkReporter::Run CreateRunReport(
+    const benchmark::internal::BenchmarkInstance& b,
+    const internal::ThreadManager::Result& results, size_t memory_iterations,
+    const MemoryManager::Result& memory_result, double seconds) {
+  // Create report about this benchmark run.
+  BenchmarkReporter::Run report;
+
+  report.run_name = b.name;
+  report.error_occurred = results.has_error_;
+  report.error_message = results.error_message_;
+  report.report_label = results.report_label_;
+  // This is the total iterations across all threads.
+  report.iterations = results.iterations;
+  report.time_unit = b.time_unit;
+
+  if (!report.error_occurred) {
+    if (b.use_manual_time) {
+      report.real_accumulated_time = results.manual_time_used;
+    } else {
+      report.real_accumulated_time = results.real_time_used;
+    }
+    report.cpu_accumulated_time = results.cpu_time_used;
+    report.complexity_n = results.complexity_n;
+    report.complexity = b.complexity;
+    report.complexity_lambda = b.complexity_lambda;
+    report.statistics = b.statistics;
+    report.counters = results.counters;
+
+    if (memory_iterations > 0) {
+      report.has_memory_result = true;
+      report.allocs_per_iter =
+          memory_iterations ? static_cast<double>(memory_result.num_allocs) /
+                                  memory_iterations
+                            : 0;
+      report.max_bytes_used = memory_result.max_bytes_used;
+    }
+
+    internal::Finish(&report.counters, results.iterations, seconds, b.threads);
+  }
+  return report;
+}
+
+// Execute one thread of benchmark b for the specified number of iterations.
+// Adds the stats collected for the thread into *total.
+void RunInThread(const BenchmarkInstance* b, size_t iters, int thread_id,
+                 ThreadManager* manager) {
+  internal::ThreadTimer timer;
+  State st = b->Run(iters, thread_id, &timer, manager);
+  CHECK(st.iterations() >= st.max_iterations)
+      << "Benchmark returned before State::KeepRunning() returned false!";
+  {
+    MutexLock l(manager->GetBenchmarkMutex());
+    internal::ThreadManager::Result& results = manager->results;
+    results.iterations += st.iterations();
+    results.cpu_time_used += timer.cpu_time_used();
+    results.real_time_used += timer.real_time_used();
+    results.manual_time_used += timer.manual_time_used();
+    results.complexity_n += st.complexity_length_n();
+    internal::Increment(&results.counters, st.counters);
+  }
+  manager->NotifyThreadComplete();
+}
+
+class BenchmarkRunner {
+ public:
+  BenchmarkRunner(const benchmark::internal::BenchmarkInstance& b_,
+                  std::vector<BenchmarkReporter::Run>* complexity_reports_)
+      : b(b_),
+        complexity_reports(*complexity_reports_),
+        min_time(!IsZero(b.min_time) ? b.min_time : FLAGS_benchmark_min_time),
+        repeats(b.repetitions != 0 ? b.repetitions
+                                   : FLAGS_benchmark_repetitions),
+        has_explicit_iteration_count(b.iterations != 0),
+        pool(b.threads - 1),
+        iters(has_explicit_iteration_count ? b.iterations : 1) {
+    run_results.display_report_aggregates_only =
+        (FLAGS_benchmark_report_aggregates_only ||
+         FLAGS_benchmark_display_aggregates_only);
+    run_results.file_report_aggregates_only =
+        FLAGS_benchmark_report_aggregates_only;
+    if (b.aggregation_report_mode != internal::ARM_Unspecified) {
+      run_results.display_report_aggregates_only =
+          (b.aggregation_report_mode &
+           internal::ARM_DisplayReportAggregatesOnly);
+      run_results.file_report_aggregates_only =
+          (b.aggregation_report_mode & internal::ARM_FileReportAggregatesOnly);
+    }
+
+    for (int repetition_num = 0; repetition_num < repeats; repetition_num++) {
+      const bool is_the_first_repetition = repetition_num == 0;
+      DoOneRepetition(is_the_first_repetition);
+    }
+
+    // Calculate additional statistics
+    run_results.aggregates_only = ComputeStats(run_results.non_aggregates);
+
+    // Maybe calculate complexity report
+    if ((b.complexity != oNone) && b.last_benchmark_instance) {
+      auto additional_run_stats = ComputeBigO(complexity_reports);
+      run_results.aggregates_only.insert(run_results.aggregates_only.end(),
+                                         additional_run_stats.begin(),
+                                         additional_run_stats.end());
+      complexity_reports.clear();
+    }
+  }
+
+  RunResults&& get_results() { return std::move(run_results); }
+
+ private:
+  RunResults run_results;
+
+  const benchmark::internal::BenchmarkInstance& b;
+  std::vector<BenchmarkReporter::Run>& complexity_reports;
+
+  const double min_time;
+  const int repeats;
+  const bool has_explicit_iteration_count;
+
+  std::vector<std::thread> pool;
+
+  size_t iters;  // preserved between repetitions!
+  // So only the first repetition has to find/calculate it,
+  // the other repetitions will just use that precomputed iteration count.
+
+  struct IterationResults {
+    internal::ThreadManager::Result results;
+    size_t iters;
+    double seconds;
+  };
+  IterationResults DoNIterations() {
+    VLOG(2) << "Running " << b.name << " for " << iters << "\n";
+
+    std::unique_ptr<internal::ThreadManager> manager;
+    manager.reset(new internal::ThreadManager(b.threads));
+
+    // Run all but one thread in separate threads
+    for (std::size_t ti = 0; ti < pool.size(); ++ti) {
+      pool[ti] = std::thread(&RunInThread, &b, iters, static_cast<int>(ti + 1),
+                             manager.get());
+    }
+    // And run one thread here directly.
+    // (If we were asked to run just one thread, we don't create new threads.)
+    // Yes, we need to do this here *after* we start the separate threads.
+    RunInThread(&b, iters, 0, manager.get());
+
+    // The main thread has finished. Now let's wait for the other threads.
+    manager->WaitForAllThreads();
+    for (std::thread& thread : pool) thread.join();
+
+    IterationResults i;
+    // Acquire the measurements/counters from the manager, UNDER THE LOCK!
+    {
+      MutexLock l(manager->GetBenchmarkMutex());
+      i.results = manager->results;
+    }
+
+    // And get rid of the manager.
+    manager.reset();
+
+    // Adjust real/manual time stats since they were reported per thread.
+    i.results.real_time_used /= b.threads;
+    i.results.manual_time_used /= b.threads;
+
+    VLOG(2) << "Ran in " << i.results.cpu_time_used << "/"
+            << i.results.real_time_used << "\n";
+
+    // So for how long were we running?
+    i.iters = iters;
+    // Base decisions off of real time if requested by this benchmark.
+    i.seconds = i.results.cpu_time_used;
+    if (b.use_manual_time) {
+      i.seconds = i.results.manual_time_used;
+    } else if (b.use_real_time) {
+      i.seconds = i.results.real_time_used;
+    }
+
+    return i;
+  }
+
+  size_t PredictNumItersNeeded(const IterationResults& i) const {
+    // See how much iterations should be increased by.
+    // Note: Avoid division by zero with max(seconds, 1ns).
+    double multiplier = min_time * 1.4 / std::max(i.seconds, 1e-9);
+    // If our last run was at least 10% of FLAGS_benchmark_min_time then we
+    // use the multiplier directly.
+    // Otherwise we use at most 10 times expansion.
+    // NOTE: When the last run was at least 10% of the min time the max
+    // expansion should be 14x.
+    bool is_significant = (i.seconds / min_time) > 0.1;
+    multiplier = is_significant ? multiplier : std::min(10.0, multiplier);
+    if (multiplier <= 1.0) multiplier = 2.0;
+
+    // So what seems to be the sufficiently-large iteration count? Round up.
+    const size_t max_next_iters =
+        0.5 + std::max(multiplier * i.iters, i.iters + 1.0);
+    // But we do have *some* sanity limits though..
+    const size_t next_iters = std::min(max_next_iters, kMaxIterations);
+
+    VLOG(3) << "Next iters: " << next_iters << ", " << multiplier << "\n";
+    return next_iters;  // round up before conversion to integer.
+  }
+
+  bool ShouldReportIterationResults(const IterationResults& i) const {
+    // Determine if this run should be reported;
+    // Either it has run for a sufficient amount of time
+    // or because an error was reported.
+    return i.results.has_error_ ||
+           i.iters >= kMaxIterations ||  // Too many iterations already.
+           i.seconds >= min_time ||      // The elapsed time is large enough.
+           // CPU time is specified but the elapsed real time greatly exceeds
+           // the minimum time.
+           // Note that user provided timers are except from this sanity check.
+           ((i.results.real_time_used >= 5 * min_time) && !b.use_manual_time);
+  }
+
+  void DoOneRepetition(bool is_the_first_repetition) {
+    IterationResults i;
+
+    // We *may* be gradually increasing the length (iteration count)
+    // of the benchmark until we decide the results are significant.
+    // And once we do, we report those last results and exit.
+    // Please do note that the if there are repetitions, the iteration count
+    // is *only* calculated for the *first* repetition, and other repetitions
+    // simply use that precomputed iteration count.
+    for (;;) {
+      i = DoNIterations();
+
+      // Do we consider the results to be significant?
+      // If we are doing repetitions, and the first repetition was already done,
+      // it has calculated the correct iteration time, so we have run that very
+      // iteration count just now. No need to calculate anything. Just report.
+      // Else, the normal rules apply.
+      const bool results_are_significant = !is_the_first_repetition ||
+                                           has_explicit_iteration_count ||
+                                           ShouldReportIterationResults(i);
+
+      if (results_are_significant) break;  // Good, let's report them!
+
+      // Nope, bad iteration. Let's re-estimate the hopefully-sufficient
+      // iteration count, and run the benchmark again...
+
+      iters = PredictNumItersNeeded(i);
+      assert(iters > i.iters &&
+             "if we did more iterations than we want to do the next time, "
+             "then we should have accepted the current iteration run.");
+    }
+
+    // Oh, one last thing, we need to also produce the 'memory measurements'..
+    MemoryManager::Result memory_result;
+    size_t memory_iterations = 0;
+    if (memory_manager != nullptr) {
+      // Only run a few iterations to reduce the impact of one-time
+      // allocations in benchmarks that are not properly managed.
+      memory_iterations = std::min<size_t>(16, iters);
+      memory_manager->Start();
+      std::unique_ptr<internal::ThreadManager> manager;
+      manager.reset(new internal::ThreadManager(1));
+      RunInThread(&b, memory_iterations, 0, manager.get());
+      manager->WaitForAllThreads();
+      manager.reset();
+
+      memory_manager->Stop(&memory_result);
+    }
+
+    // Ok, now actualy report.
+    BenchmarkReporter::Run report = CreateRunReport(
+        b, i.results, memory_iterations, memory_result, i.seconds);
+
+    if (!report.error_occurred && b.complexity != oNone)
+      complexity_reports.push_back(report);
+
+    run_results.non_aggregates.push_back(report);
+  }
+};
+
+}  // end namespace
+
+RunResults RunBenchmark(
+    const benchmark::internal::BenchmarkInstance& b,
+    std::vector<BenchmarkReporter::Run>* complexity_reports) {
+  internal::BenchmarkRunner r(b, complexity_reports);
+  return r.get_results();
+}
+
+}  // end namespace internal
+
+}  // end namespace benchmark