From a0cbb80f581d691c02bd932169f39c7a876c11ee Mon Sep 17 00:00:00 2001
From: Hao Chen <chenhaosjtuacm@google.com>
Date: Mon, 8 Mar 2021 12:04:00 -0800
Subject: [PATCH] Gracefully stop the GeneratorHub worker thread in destructor

To unit test the virtualized VHAL, GeneratorHub needs to be destructable

Test: run unit tests in pa/1878260
Bug: 181371253
Change-Id: Icfd3007a194da7ade037e359858b3dd48f24a0d6
---
 .../2.0/default/impl/vhal_v2_0/GeneratorHub.cpp | 17 ++++++++++++++---
 .../2.0/default/impl/vhal_v2_0/GeneratorHub.h   |  3 ++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.cpp b/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.cpp
index 548285abfb..9be9ea7c8e 100644
--- a/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.cpp
+++ b/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.cpp
@@ -31,6 +31,14 @@ namespace impl {
 GeneratorHub::GeneratorHub(const OnHalEvent& onHalEvent)
     : mOnHalEvent(onHalEvent), mThread(&GeneratorHub::run, this) {}
 
+GeneratorHub::~GeneratorHub() {
+    mShuttingDownFlag.store(true);
+    mCond.notify_all();
+    if (mThread.joinable()) {
+        mThread.join();
+    }
+}
+
 void GeneratorHub::registerGenerator(int32_t cookie, FakeValueGeneratorPtr generator) {
     {
         std::lock_guard<std::mutex> g(mLock);
@@ -58,15 +66,18 @@ void GeneratorHub::unregisterGenerator(int32_t cookie) {
 }
 
 void GeneratorHub::run() {
-    while (true) {
+    while (!mShuttingDownFlag.load()) {
         std::unique_lock<std::mutex> g(mLock);
         // Pop events whose generator does not exist (may be already unregistered)
         while (!mEventQueue.empty()
                && mGenerators.find(mEventQueue.top().cookie) == mGenerators.end()) {
              mEventQueue.pop();
         }
-        // Wait until event queue is not empty
-        mCond.wait(g, [this] { return !mEventQueue.empty(); });
+        // Wait until event queue is not empty or shutting down flag is set
+        mCond.wait(g, [this] { return !mEventQueue.empty() || mShuttingDownFlag.load(); });
+        if (mShuttingDownFlag.load()) {
+            break;
+        }
 
         const VhalEvent& curEvent = mEventQueue.top();
 
diff --git a/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.h b/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.h
index dcf6a4f06e..b25dbf1c09 100644
--- a/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.h
+++ b/automotive/vehicle/2.0/default/impl/vhal_v2_0/GeneratorHub.h
@@ -58,7 +58,7 @@ private:
 
 public:
     GeneratorHub(const OnHalEvent& onHalEvent);
-    ~GeneratorHub() = default;
+    ~GeneratorHub();
 
     /**
      * Register a new generator. The generator will be discarded if it could not produce next event.
@@ -84,6 +84,7 @@ private:
     mutable std::mutex mLock;
     std::condition_variable mCond;
     std::thread mThread;
+    std::atomic<bool> mShuttingDownFlag{false};
 };
 
 }  // namespace impl