From 0f76e090f18605286352ee92020efcb3556d4d69 Mon Sep 17 00:00:00 2001
From: Andrii Grynenko <andrii@fb.com>
Date: Fri, 20 May 2016 15:55:24 -0700
Subject: [PATCH] Make outstanding LoopKeepAlive hold EventBase destructor

Summary:
LoopKeepAlive handle can be grabbed to signal that some external event will later be scheduled on the EventBase via runInEventBaseThread. Usually the code which will be calling runInEventBaseThread only has a raw pointer to an EventBase, so it doesn't have any way to know it was destroyed.

This change ensures that EventBase destructor will keep running the event loop until all such LoopKeepAlive handles are released.

Reviewed By: yfeldblum

Differential Revision: D3323835

fbshipit-source-id: 4071dae691a61dfebe2f1759cf99f661b161fa4a
---
 folly/io/async/EventBase.cpp          |  8 ++++++++
 folly/io/async/test/EventBaseTest.cpp | 28 +++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/folly/io/async/EventBase.cpp b/folly/io/async/EventBase.cpp
index 5c0b7812..0987f1fa 100644
--- a/folly/io/async/EventBase.cpp
+++ b/folly/io/async/EventBase.cpp
@@ -195,6 +195,14 @@ EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
 }
 
 EventBase::~EventBase() {
+  // Keep looping until all keep-alive handles are released. Each keep-alive
+  // handle signals that some external code will still schedule some work on
+  // this EventBase (so it's not safe to destroy it).
+  while (!loopKeepAlive_.unique()) {
+    applyLoopKeepAlive();
+    loopOnce();
+  }
+
   // Call all destruction callbacks, before we start cleaning up our state.
   while (!onDestructionCallbacks_.empty()) {
     LoopCallback* callback = &onDestructionCallbacks_.front();
diff --git a/folly/io/async/test/EventBaseTest.cpp b/folly/io/async/test/EventBaseTest.cpp
index 7cb49a4d..46840882 100644
--- a/folly/io/async/test/EventBaseTest.cpp
+++ b/folly/io/async/test/EventBaseTest.cpp
@@ -1736,7 +1736,8 @@ TEST(EventBaseTest, LoopKeepAlive) {
   std::thread t([&, loopKeepAlive = evb.loopKeepAlive() ] {
     /* sleep override */ std::this_thread::sleep_for(
         std::chrono::milliseconds(100));
-    evb.runInEventBaseThread([&] { done = true; });
+    evb.runInEventBaseThread(
+        [&done, loopKeepAlive = std::move(loopKeepAlive) ] { done = true; });
   });
 
   evb.loop();
@@ -1756,7 +1757,8 @@ TEST(EventBaseTest, LoopKeepAliveInLoop) {
     t = std::thread([&, loopKeepAlive = evb.loopKeepAlive() ] {
       /* sleep override */ std::this_thread::sleep_for(
           std::chrono::milliseconds(100));
-      evb.runInEventBaseThread([&] { done = true; });
+      evb.runInEventBaseThread(
+          [&done, loopKeepAlive = std::move(loopKeepAlive) ] { done = true; });
     });
   });
 
@@ -1766,3 +1768,25 @@ TEST(EventBaseTest, LoopKeepAliveInLoop) {
 
   t.join();
 }
+
+TEST(EventBaseTest, LoopKeepAliveShutdown) {
+  auto evb = folly::make_unique<EventBase>();
+
+  bool done = false;
+
+  std::thread t(
+      [&done, loopKeepAlive = evb->loopKeepAlive(), evbPtr = evb.get() ] {
+        /* sleep override */ std::this_thread::sleep_for(
+            std::chrono::milliseconds(100));
+        evbPtr->runInEventBaseThread(
+            [&done, loopKeepAlive = std::move(loopKeepAlive) ] {
+              done = true;
+            });
+      });
+
+  evb.reset();
+
+  ASSERT_TRUE(done);
+
+  t.join();
+}
-- 
2.34.1