MDEV-19826 10.4 seems to crash with "pool-of-threads" (#1370)

MariaDB 10.4 was crashing when thread-handling was set to
pool-of-threads and wsrep was enabled.

There were two apparent reasons for the crash:
- Connection handling in threadpool_common.cc was missing calls to
  control wsrep client state.
- Thread specific storage which contains thread variables (THR_KEY_mysys)
  was not handled appropriately by wsrep patch when pool-of-threads
  was configured.

This patch addresses the above issues in the following way:
- Wsrep client state open/close was moved in thd_prepare_connection() and
  end_connection() to have common handling for one-thread-per-connection
  and pool-of-threads.
- Thread local storage handling in wsrep patch was reworked by introducing
  set of wsrep_xxx_threadvars() calls which replace calls to
  THD store_globals()/reset_globals() and deal with thread handling
  specifics internally.

Wsrep-lib was updated to version which relaxes internal concurrency
related sanity checks.

Rollback code from wsrep_rollback_process() was extracted to separate calls
for better readability.

Post rollback thread was removed as it was completely unused.

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/wsrep_trans_observer.h b/sql/wsrep_trans_observer.h
index 64ac80783c9..6bb26c40064 100644
--- a/sql/wsrep_trans_observer.h
+++ b/sql/wsrep_trans_observer.h
@@ -422,6 +422,17 @@ static inline void wsrep_close(THD* thd)
   DBUG_VOID_RETURN;
 }
 
+static inline void
+wsrep_wait_rollback_complete_and_acquire_ownership(THD *thd)
+{
+  DBUG_ENTER("wsrep_wait_rollback_complete_and_acquire_ownership");
+  if (thd->wsrep_cs().state() != wsrep::client_state::s_none)
+  {
+    thd->wsrep_cs().wait_rollback_complete_and_acquire_ownership();
+  }
+  DBUG_VOID_RETURN;
+}
+
 static inline int wsrep_before_command(THD* thd)
 {
   return (thd->wsrep_cs().state() != wsrep::client_state::s_none ?