Throttle: add BackoffThrottle unit tests

Signed-off-by: Samuel Just <sjust@redhat.com>

src/test/common/Throttle.cc

@@ -28,6 +28,13 @@
 #include "global/global_init.h"
 #include <gtest/gtest.h>
 
+#include <thread>
+#include <atomic>
+#include <chrono>
+#include <mutex>
+#include <list>
+#include <random>
+
 class ThrottleTest : public ::testing::Test {
 protected:
 
@@ -252,6 +259,159 @@ TEST_F(ThrottleTest, destructor) {
   }
 }
 
+std::pair<double, std::chrono::duration<double> > test_backoff(
+  double low_threshhold,
+  double high_threshhold,
+  double expected_throughput,
+  double high_multiple,
+  double max_multiple,
+  uint64_t max,
+  double put_delay_per_count,
+  unsigned getters,
+  unsigned putters)
+{
+  std::mutex l;
+  std::condition_variable c;
+  uint64_t total = 0;
+  std::list<uint64_t> in_queue;
+  bool stop = false;
+
+  auto wait_time = std::chrono::duration<double>(0);
+  uint64_t waits = 0;
+
+  uint64_t total_observed_total = 0;
+  uint64_t total_observations = 0;
+
+  BackoffThrottle throttle(5);
+  bool valid = throttle.set_params(
+    low_threshhold,
+    high_threshhold,
+    expected_throughput,
+    high_multiple,
+    max_multiple,
+    max,
+    0);
+  assert(valid);
+
+  auto getter = [&]() {
+    std::random_device rd;
+    std::mt19937 gen(rd());
+    std::uniform_int_distribution<> dis(0, 10);
+
+    std::unique_lock<std::mutex> g(l);
+    while (!stop) {
+      g.unlock();
+
+      uint64_t to_get = dis(gen);
+      auto waited = throttle.get(to_get);
+
+      g.lock();
+      wait_time += waited;
+      waits += to_get;
+      total += to_get;
+      in_queue.push_back(to_get);
+      c.notify_one();
+    }
+  };
+
+  auto putter = [&]() {
+    std::unique_lock<std::mutex> g(l);
+    while (!stop) {
+      while (in_queue.empty())
+	c.wait(g);
+
+      uint64_t c = in_queue.front();
+
+      total_observed_total += total;
+      total_observations++;
+      in_queue.pop_front();
+      assert(total <= max);
+
+      g.unlock();
+      std::this_thread::sleep_for(
+	c * std::chrono::duration<double>(put_delay_per_count*putters));
+      g.lock();
+
+      total -= c;
+      throttle.put(c);
+    }
+  };
+
+  vector<std::thread> gts(getters);
+  for (auto &&i: gts) i = std::thread(getter);
+
+  vector<std::thread> pts(putters);
+  for (auto &&i: pts) i = std::thread(putter);
+
+  std::this_thread::sleep_for(std::chrono::duration<double>(5));
+  {
+    std::unique_lock<std::mutex> g(l);
+    stop = true;
+  }
+  for (auto &&i: gts) i.join();
+  gts.clear();
+  for (auto &&i: pts) i.join();
+  pts.clear();
+
+  return make_pair(
+    ((double)total_observed_total)/((double)total_observations),
+    wait_time / waits);
+}
+
+TEST(BackoffThrottle, undersaturated)
+{
+  auto results = test_backoff(
+    0.4,
+    0.6,
+    1000,
+    2,
+    10,
+    100,
+    0.0001,
+    3,
+    6);
+  ASSERT_LT(results.first, 45);
+  ASSERT_GT(results.first, 35);
+  ASSERT_LT(results.second.count(), 0.0002);
+  ASSERT_GT(results.second.count(), 0.00005);
+}
+
+TEST(BackoffThrottle, balanced)
+{
+  auto results = test_backoff(
+    0.4,
+    0.6,
+    1000,
+    2,
+    10,
+    100,
+    0.001,
+    7,
+    2);
+  ASSERT_LT(results.first, 60);
+  ASSERT_GT(results.first, 40);
+  ASSERT_LT(results.second.count(), 0.002);
+  ASSERT_GT(results.second.count(), 0.0005);
+}
+
+TEST(BackoffThrottle, oversaturated)
+{
+  auto results = test_backoff(
+    0.4,
+    0.6,
+    10000000,
+    2,
+    10,
+    100,
+    0.001,
+    1,
+    3);
+  ASSERT_LT(results.first, 101);
+  ASSERT_GT(results.first, 85);
+  ASSERT_LT(results.second.count(), 0.002);
+  ASSERT_GT(results.second.count(), 0.0005);
+}
+
 int main(int argc, char **argv) {
   vector<const char*> args;
   argv_to_vec(argc, (const char **)argv, args);