Merge pull request #17151 from arjunroy/grpc_memleak_fix

Fixed intermittent CPP sync server shutdown leak.

src/cpp/server/server_cc.cc

@@ -202,9 +202,21 @@ class Server::SyncRequest final : public internal::CompletionQueueTag {
     }
   }
 
+  void PostShutdownCleanup() {
+    if (call_) {
+      grpc_call_unref(call_);
+      call_ = nullptr;
+    }
+    if (cq_) {
+      grpc_completion_queue_destroy(cq_);
+      cq_ = nullptr;
+    }
+  }
+
   bool FinalizeResult(void** tag, bool* status) override {
     if (!*status) {
       grpc_completion_queue_destroy(cq_);
+      cq_ = nullptr;
     }
     if (call_details_) {
       deadline_ = call_details_->deadline;
@@ -589,7 +601,17 @@ class Server::SyncRequestThreadManager : public ThreadManager {
     void* tag;
     bool ok;
     while (server_cq_->Next(&tag, &ok)) {
-      // Do nothing
+      if (ok) {
+        // If a request was pulled off the queue, it means that the thread
+        // handling the request added it to the completion queue after shutdown
+        // was called - because the thread had already started and checked the
+        // shutdown flag before shutdown was called. In this case, we simply
+        // clean it up here, *after* calling wait on all the worker threads, at
+        // which point we are certain no in-flight requests will add more to the
+        // queue. This fixes an intermittent memory leak on shutdown.
+        SyncRequest* sync_req = static_cast<SyncRequest*>(tag);
+        sync_req->PostShutdownCleanup();
+      }
     }
   }