#3750: [docdb] Deregister callback for common mem trackers from root …

…mem tracker in destructor of vector

Summary:
Tree of `MemTrackers` is organized so that a node maintains pointers to all nodes along the path to root. Hence (almost) all traversal is in the upward direction. But common `MemTracker`s are accessed from the root - i.e., in the         downward direction. In the destructor of a common `MemTracker`, an upward traversal to root is followed by a downward traversal back into vector of common `MemTracker`s. This vector should not be accessed by root mem tracker once any     common mem tracker in it is destroyed.

Prevent vector access from root mem tracker by setting the lambda for downward traversal to null in the destructor of vector.

Test Plan: Jenkins

Reviewers: amitanand, bogdan, sergei

Reviewed By: sergei

Subscribers: ybase

Differential Revision: https://phabricator.dev.yugabyte.com/D8087

src/yb/server/server_base.cc

@@ -117,7 +117,19 @@ AtomicInt<int32_t> mem_tracker_id_counter(-1);
 
 std::string kServerMemTrackerName = "server";
 
-std::vector<MemTrackerPtr> common_mem_trackers;
+struct CommonMemTrackers {
+  std::vector<MemTrackerPtr> trackers;
+
+  ~CommonMemTrackers() {
+#if defined(TCMALLOC_ENABLED)
+    // Prevent root mem tracker from accessing common mem trackers.
+    auto root = MemTracker::GetRootTracker();
+    root->SetPollChildrenConsumptionFunctors(nullptr);
+#endif
+  }
+};
+
+std::unique_ptr<CommonMemTrackers> common_mem_trackers;
 
 } // anonymous namespace
 
@@ -132,7 +144,7 @@ std::shared_ptr<MemTracker> CreateMemTrackerForServer() {
 
 #if defined(TCMALLOC_ENABLED)
 void RegisterTCMallocTracker(const char* name, const char* prop) {
-  common_mem_trackers.push_back(MemTracker::CreateTracker(
+  common_mem_trackers->trackers.push_back(MemTracker::CreateTracker(
       -1, "TCMalloc "s + name, std::bind(&MemTracker::GetTCMallocProperty, prop)));
 }
 #endif
@@ -155,14 +167,16 @@ RpcServerBase::RpcServerBase(string name, const ServerBaseOptions& options,
   // When mem tracker for first server is created we register mem trackers that report tc malloc
   // status.
   if (mem_tracker_->id() == kServerMemTrackerName) {
+    common_mem_trackers = std::make_unique<CommonMemTrackers>();
+
     RegisterTCMallocTracker("Thread Cache", "tcmalloc.thread_cache_free_bytes");
     RegisterTCMallocTracker("Central Cache", "tcmalloc.central_cache_free_bytes");
     RegisterTCMallocTracker("Transfer Cache", "tcmalloc.transfer_cache_free_bytes");
     RegisterTCMallocTracker("PageHeap Free", "tcmalloc.pageheap_free_bytes");
 
     auto root = MemTracker::GetRootTracker();
     root->SetPollChildrenConsumptionFunctors([]() {
-          for (auto& tracker : common_mem_trackers) {
+          for (auto& tracker : common_mem_trackers->trackers) {
             tracker->UpdateConsumption();
           }
         });