Implement an event-based simulator for QuicConnection

net/quic/core/congestion_control/simulation/simulator.cc

Index: net/quic/core/congestion_control/simulation/simulator.cc
diff --git a/net/quic/core/congestion_control/simulation/simulator.cc b/net/quic/core/congestion_control/simulation/simulator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4c91be1863be5b4c264a4673254f424eb567d317
--- /dev/null
+++ b/net/quic/core/congestion_control/simulation/simulator.cc
@@ -0,0 +1,112 @@
+#include "net/quic/core/congestion_control/simulation/simulator.h"
+#include "net/quic/core/crypto/quic_random.h"
+#include "util/gtl/ptr_util.h"
+
+namespace net {
+namespace simulation {
+
+Simulator::Simulator()
+    : random_generator_(nullptr),
+      alarm_factory_(this, "Default Alarm Manager") {}
+
+Simulator::Clock::Clock() : now_(kStartTime) {}
+
+QuicTime Simulator::Clock::ApproximateNow() const {
+  return now_;
+}
+
+QuicTime Simulator::Clock::Now() const {
+  return now_;
+}
+
+QuicWallTime Simulator::Clock::WallNow() const {
+  return QuicWallTime::FromUNIXMicroseconds(
+      (now_ - QuicTime::Zero()).ToMicroseconds());
+}
+
+void Simulator::AddActor(Actor* actor) {
+  auto emplace_times_result =
+      scheduled_times_.emplace(actor, QuicTime::Infinite());
+  auto emplace_names_result = actor_names_.emplace(actor->name());
+
+  // Ensure that the object was actually placed into the map.
+  DCHECK(emplace_times_result.second);
+  DCHECK(emplace_names_result.second);
+}
+
+void Simulator::Schedule(Actor* actor, QuicTime new_time) {
+  auto scheduled_time_it = scheduled_times_.find(actor);
+  DCHECK(scheduled_time_it != scheduled_times_.end());
+  QuicTime scheduled_time = scheduled_time_it->second;
+
+  if (scheduled_time <= new_time) {
+    return;
+  }
+
+  if (scheduled_time != QuicTime::Infinite()) {
+    Unschedule(actor);
+  }
+
+  scheduled_time_it->second = new_time;
+  schedule_.insert(std::make_pair(new_time, actor));
+}
+
+void Simulator::Unschedule(Actor* actor) {
+  auto scheduled_time_it = scheduled_times_.find(actor);
+  DCHECK(scheduled_time_it != scheduled_times_.end());
+  QuicTime scheduled_time = scheduled_time_it->second;
+
+  DCHECK(scheduled_time != QuicTime::Infinite());
+  auto range = schedule_.equal_range(scheduled_time);
+  for (auto it = range.first; it != range.second; ++it) {
+    if (it->second == actor) {
+      schedule_.erase(it);
+      scheduled_time_it->second = QuicTime::Infinite();
+      return;
+    }
+  }
+  DCHECK(false);
+}
+
+const QuicClock* Simulator::GetClock() const {
+  return &clock_;
+}
+
+QuicRandom* Simulator::GetRandomGenerator() {
+  if (random_generator_ == nullptr) {
+    random_generator_ = QuicRandom::GetInstance();
+  }
+
+  return random_generator_;
+}
+
+QuicBufferAllocator* Simulator::GetBufferAllocator() {
+  return &buffer_allocator_;
+}
+
+QuicAlarmFactory* Simulator::GetAlarmFactory() {
+  return &alarm_factory_;
+}
+
+void Simulator::HandleNextScheduledActor() {
+  const auto current_event_it = schedule_.begin();
+  QuicTime event_time = current_event_it->first;
+  Actor* actor = current_event_it->second;
+  DVLOG(3) << "At t = " << event_time.ToDebuggingValue() << ", calling "
+           << actor->name();
+
+  Unschedule(actor);
+
+  if (clock_.Now() > event_time) {
+    QUIC_BUG << "Error: event registered by [" << actor->name()
+             << "] requires travelling back in time.  Current time: "
+             << clock_.Now().ToDebuggingValue()
+             << ", scheduled time: " << event_time.ToDebuggingValue();
+  }
+  clock_.now_ = event_time;
+
+  actor->Act();
+}
+
+}  // namespace simulation
+}  // namespace net