Attempt to fix race condition in recursive RWLock

dbms/src/Common/RWLock.cpp

@@ -122,6 +122,9 @@ RWLockImpl::LockHolder RWLockImpl::getLock(RWLockImpl::Type type, const String &
 
     LockHolder res(new LockHolderImpl(shared_from_this(), it_group, it_client));
 
+    /// Wait a notification until we will be the only in the group.
+    it_group->cv.wait(lock, [&] () { return it_group == queue.begin(); });
+
     /// Insert myself (weak_ptr to the holder) to threads set to implement recursive lock
     thread_to_holder.emplace(this_thread_id, res);
     res->thread_id = this_thread_id;
@@ -130,17 +133,6 @@ RWLockImpl::LockHolder RWLockImpl::getLock(RWLockImpl::Type type, const String &
         query_id_to_holder.emplace(query_id, res);
     res->query_id = query_id;
 
-    /// We are first, we should not wait anything
-    /// If we are not the first client in the group, a notification could be already sent
-    if (it_group == queue.begin())
-    {
-        finalize_metrics();
-        return res;
-    }
-
-    /// Wait a notification
-    it_group->cv.wait(lock, [&] () { return it_group == queue.begin(); });
-
     finalize_metrics();
     return res;
 }

dbms/src/Common/RWLock.h

 #pragma once
+
 #include <Core/Types.h>
-#include <boost/core/noncopyable.hpp>
+
 #include <list>
 #include <vector>
 #include <mutex>