From b2901a450fa33618583f0e6a24c67bd50d1a3b19 Mon Sep 17 00:00:00 2001
From: Matt Klein <mklein@lyft.com>
Date: Mon, 14 Nov 2016 14:23:06 -0800
Subject: [PATCH] perf: use lock free event base

The only place we need the lock is when we do post(). Just run a timer
every 100ms and check for posted items to avoid acquiring and releasing
the lock everywhere where we don't need it.
---
 source/common/event/dispatcher_impl.cc | 32 +++++++++++---------------
 source/common/event/dispatcher_impl.h  |  1 +
 2 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/source/common/event/dispatcher_impl.cc b/source/common/event/dispatcher_impl.cc
index b54897a4b131..9a544c8bf828 100644
--- a/source/common/event/dispatcher_impl.cc
+++ b/source/common/event/dispatcher_impl.cc
@@ -17,10 +17,16 @@
 
 namespace Event {
 
-DispatcherImpl::DispatcherImpl()
-    : base_(event_base_new()),
-      deferred_delete_timer_(createTimer([this]() -> void { clearDeferredDeleteList(); })),
-      current_to_delete_(&to_delete_1_) {}
+DispatcherImpl::DispatcherImpl() : current_to_delete_(&to_delete_1_) {
+
+  event_config* config = event_config_new();
+  event_config_set_flag(config, EVENT_BASE_FLAG_NOLOCK);
+  base_.reset(event_base_new_with_config(config));
+  event_config_free(config);
+
+  deferred_delete_timer_ = createTimer([this]() -> void { clearDeferredDeleteList(); });
+  post_timer_ = createTimer([this]() -> void { runPostCallbacks(); });
+}
 
 DispatcherImpl::~DispatcherImpl() {}
 
@@ -110,20 +116,8 @@ SignalEventPtr DispatcherImpl::listenForSignal(int signal_num, SignalCb cb) {
 }
 
 void DispatcherImpl::post(std::function<void()> callback) {
-  bool do_post;
-  {
-    std::unique_lock<std::mutex> lock(post_lock_);
-    do_post = post_callbacks_.empty();
-    post_callbacks_.push_back(callback);
-  }
-
-  if (do_post) {
-    // If the dispatcher shuts down before this runs, we will leak. This never happens during
-    // normal operation so its not a big deal.
-    event_base_once(base_.get(), -1, EV_TIMEOUT, [](evutil_socket_t, short, void* arg) -> void {
-      static_cast<DispatcherImpl*>(arg)->runPostCallbacks();
-    }, this, nullptr);
-  }
+  std::unique_lock<std::mutex> lock(post_lock_);
+  post_callbacks_.push_back(callback);
 }
 
 void DispatcherImpl::run(RunType type) {
@@ -146,6 +140,8 @@ void DispatcherImpl::runPostCallbacks() {
     callback();
     lock.lock();
   }
+
+  post_timer_->enableTimer(std::chrono::milliseconds(100));
 }
 
 } // Event
diff --git a/source/common/event/dispatcher_impl.h b/source/common/event/dispatcher_impl.h
index 396297275a24..4e53f3943eb4 100644
--- a/source/common/event/dispatcher_impl.h
+++ b/source/common/event/dispatcher_impl.h
@@ -47,6 +47,7 @@ class DispatcherImpl : Logger::Loggable<Logger::Id::main>, public Dispatcher {
 
   Libevent::BasePtr base_;
   TimerPtr deferred_delete_timer_;
+  TimerPtr post_timer_;
   std::vector<DeferredDeletablePtr> to_delete_1_;
   std::vector<DeferredDeletablePtr> to_delete_2_;
   std::vector<DeferredDeletablePtr>* current_to_delete_;