Stabilize hci_layer_test

Currently this test fails around 1 every 10 runs, with null pointer
exception.

Bug: 177907117
Tag: #feature
Test: atest bluetooth_test_gd --gtest_filter=HciTest.receiveMultiple* --gtest_repeat=100
Change-Id: I58de30ae493dc1a2764e36a4451906218632fd47

system/gd/hci/hci_layer_test.cc

@@ -204,6 +204,7 @@ class DependsOnHci : public Module {
   }
 
   EventView GetReceivedEvent() {
+    std::lock_guard<std::mutex> lock(list_protector_);
     EventView packetview = incoming_events_.front();
     incoming_events_.pop_front();
     return packetview;
@@ -220,6 +221,7 @@ class DependsOnHci : public Module {
   }
 
   AclView GetReceivedAcl() {
+    std::lock_guard<std::mutex> lock(list_protector_);
     AclView packetview = incoming_acl_packets_.front();
     incoming_acl_packets_.pop_front();
     return packetview;
@@ -253,8 +255,11 @@ class DependsOnHci : public Module {
   std::list<AclView> incoming_acl_packets_;
   std::unique_ptr<std::promise<void>> event_promise_;
   std::unique_ptr<std::promise<void>> acl_promise_;
+  /* This mutex is protecting lists above from being pushed/popped from different threads at same time */
+  std::mutex list_protector_;
 
   void handle_acl() {
+    std::lock_guard<std::mutex> lock(list_protector_);
     auto acl_ptr = hci_->GetAclQueueEnd()->TryDequeue();
     incoming_acl_packets_.push_back(*acl_ptr);
     if (acl_promise_ != nullptr) {
@@ -266,6 +271,7 @@ class DependsOnHci : public Module {
 
   template <typename T>
   void handle_event(T event) {
+    std::lock_guard<std::mutex> lock(list_protector_);
     incoming_events_.push_back(event);
     if (event_promise_ != nullptr) {
       auto promise = std::move(event_promise_);
@@ -688,7 +694,7 @@ TEST_F(HciTest, receiveMultipleAclPackets) {
   Address bd_addr;
   ASSERT_TRUE(Address::FromString("A1:A2:A3:A4:A5:A6", bd_addr));
   uint16_t handle = 0x0001;
-  uint16_t num_packets = 100;
+  const uint16_t num_packets = 100;
   PacketBoundaryFlag packet_boundary_flag = PacketBoundaryFlag::FIRST_AUTOMATICALLY_FLUSHABLE;
   BroadcastFlag broadcast_flag = BroadcastFlag::POINT_TO_POINT;
   for (uint16_t i = 0; i < num_packets; i++) {
@@ -702,15 +708,15 @@ TEST_F(HciTest, receiveMultipleAclPackets) {
   auto incoming_acl_future = upper->GetReceivedAclFuture();
   uint16_t received_packets = 0;
   while (received_packets < num_packets - 1) {
-    size_t num_packets = upper->GetNumReceivedAclPackets();
-    if (num_packets == 0) {
+    size_t num_rcv_packets = upper->GetNumReceivedAclPackets();
+    if (num_rcv_packets == 0) {
       auto incoming_acl_status = incoming_acl_future.wait_for(kAclTimeout);
       // Get the next future.
       ASSERT_EQ(incoming_acl_status, std::future_status::ready);
       incoming_acl_future = upper->GetReceivedAclFuture();
-      num_packets = upper->GetNumReceivedAclPackets();
+      num_rcv_packets = upper->GetNumReceivedAclPackets();
     }
-    for (size_t i = 0; i < num_packets; i++) {
+    for (size_t i = 0; i < num_rcv_packets; i++) {
       auto acl_view = upper->GetReceivedAcl();
       ASSERT_TRUE(acl_view.IsValid());
       ASSERT_EQ(bd_addr.length() + sizeof(handle) + sizeof(received_packets), acl_view.GetPayload().size());