From 59408f12857c269b6a28ce863ac7086f8ce5b4a6 Mon Sep 17 00:00:00 2001
From: AJ Heller <hork@google.com>
Date: Wed, 15 Nov 2023 13:03:54 -0800
Subject: [PATCH] [EventEngine] Use EventEngine::Run for TimerManager's
 MainLoop (#34705)

Closes #34705

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/34705 from drfloob:timer-mgr-on-ee-alt 070118e3f1ae42e5ec9933d327ab170653f65594
PiperOrigin-RevId: 582778797
---
 .../posix_engine/timer_manager.cc             | 44 +++++++------------
 .../event_engine/posix_engine/timer_manager.h |  3 --
 2 files changed, 17 insertions(+), 30 deletions(-)

diff --git a/src/core/lib/event_engine/posix_engine/timer_manager.cc b/src/core/lib/event_engine/posix_engine/timer_manager.cc
index 2962f7a2eb9..4df2dc7ba28 100644
--- a/src/core/lib/event_engine/posix_engine/timer_manager.cc
+++ b/src/core/lib/event_engine/posix_engine/timer_manager.cc
@@ -30,7 +30,6 @@
 #include <grpc/support/time.h>
 
 #include "src/core/lib/debug/trace.h"
-#include "src/core/lib/gprpp/thd.h"
 
 static thread_local bool g_timer_thread;
 
@@ -67,41 +66,32 @@ bool TimerManager::WaitUntil(grpc_core::Timestamp next) {
 }
 
 void TimerManager::MainLoop() {
-  for (;;) {
-    grpc_core::Timestamp next = grpc_core::Timestamp::InfFuture();
-    absl::optional<std::vector<experimental::EventEngine::Closure*>>
-        check_result = timer_list_->TimerCheck(&next);
-    GPR_ASSERT(check_result.has_value() &&
-               "ERROR: More than one MainLoop is running.");
-    if (!check_result->empty()) {
-      RunSomeTimers(std::move(*check_result));
-      continue;
-    }
-    if (!WaitUntil(next)) break;
+  grpc_core::Timestamp next = grpc_core::Timestamp::InfFuture();
+  absl::optional<std::vector<experimental::EventEngine::Closure*>>
+      check_result = timer_list_->TimerCheck(&next);
+  GPR_ASSERT(check_result.has_value() &&
+             "ERROR: More than one MainLoop is running.");
+  bool timers_found = !check_result->empty();
+  if (timers_found) {
+    RunSomeTimers(std::move(*check_result));
   }
-  main_loop_exit_signal_->Notify();
+  thread_pool_->Run([this, next, timers_found]() {
+    if (!timers_found && !WaitUntil(next)) {
+      main_loop_exit_signal_->Notify();
+      return;
+    }
+    MainLoop();
+  });
 }
 
 bool TimerManager::IsTimerManagerThread() { return g_timer_thread; }
 
-void TimerManager::StartMainLoopThread() {
-  main_thread_ = grpc_core::Thread(
-      "timer_manager",
-      [](void* arg) {
-        auto self = static_cast<TimerManager*>(arg);
-        self->MainLoop();
-      },
-      this, nullptr,
-      grpc_core::Thread::Options().set_tracked(false).set_joinable(false));
-  main_thread_.Start();
-}
-
 TimerManager::TimerManager(
     std::shared_ptr<grpc_event_engine::experimental::ThreadPool> thread_pool)
     : host_(this), thread_pool_(std::move(thread_pool)) {
   timer_list_ = std::make_unique<TimerList>(&host_);
   main_loop_exit_signal_.emplace();
-  StartMainLoopThread();
+  thread_pool_->Run([this]() { MainLoop(); });
 }
 
 grpc_core::Timestamp TimerManager::Host::Now() {
@@ -162,7 +152,7 @@ void TimerManager::RestartPostFork() {
   }
   shutdown_ = false;
   main_loop_exit_signal_.emplace();
-  StartMainLoopThread();
+  thread_pool_->Run([this]() { MainLoop(); });
 }
 
 void TimerManager::PrepareFork() { Shutdown(); }
diff --git a/src/core/lib/event_engine/posix_engine/timer_manager.h b/src/core/lib/event_engine/posix_engine/timer_manager.h
index 89d547a5ce7..5cd634c51b0 100644
--- a/src/core/lib/event_engine/posix_engine/timer_manager.h
+++ b/src/core/lib/event_engine/posix_engine/timer_manager.h
@@ -36,7 +36,6 @@
 #include "src/core/lib/event_engine/thread_pool/thread_pool.h"
 #include "src/core/lib/gprpp/notification.h"
 #include "src/core/lib/gprpp/sync.h"
-#include "src/core/lib/gprpp/thd.h"
 #include "src/core/lib/gprpp/time.h"
 
 namespace grpc_event_engine {
@@ -80,7 +79,6 @@ class TimerManager final : public grpc_event_engine::experimental::Forkable {
     TimerManager* const timer_manager_;
   };
 
-  void StartMainLoopThread();
   void RestartPostFork();
   void MainLoop();
   void RunSomeTimers(std::vector<experimental::EventEngine::Closure*> timers);
@@ -103,7 +101,6 @@ class TimerManager final : public grpc_event_engine::experimental::Forkable {
   uint64_t wakeups_ ABSL_GUARDED_BY(mu_) = false;
   // actual timer implementation
   std::unique_ptr<TimerList> timer_list_;
-  grpc_core::Thread main_thread_;
   std::shared_ptr<grpc_event_engine::experimental::ThreadPool> thread_pool_;
   absl::optional<grpc_core::Notification> main_loop_exit_signal_;
 };