WL#10676: DevAPI: asynchronous execution - part1 - fixes

Stmt_op could hold a reference to a cdk session that was destroyed (after
the statement has de-registered itself). Fixed by changing reference to a pointer
which is set to null when statement is de-registered from its session.

Author: rsomla1

cdk/include/mysql/cdk/mysqlx/result.h

@@ -404,7 +404,12 @@ class Stmt_op
   using Row_processor::col_count_t;
   using Row_processor::row_count_t;
 
-  Session& m_session;
+  /*
+    This points at statement's session as long as the statement is active and
+    registered with it.
+  */
+
+  Session *m_session = nullptr;
 
   /*
     If several asynchronous statements have been issued, these pointers
@@ -431,21 +436,30 @@ class Stmt_op
   Cursor *m_current_cursor = nullptr;
 
   Stmt_op(Session &s)
-    : m_session(s)
   {
-    m_session.register_stmt(this);
+    s.register_stmt(this);
+    // Note: m_session is set during registration.
+    assert(m_session);
   }
 
   virtual ~Stmt_op()
   {
     discard();
     wait();
-    m_session.deregister_stmt(this);
+    if (m_session)
+      m_session->deregister_stmt(this);
+  }
+
+  Session& get_session()
+  {
+    // Note: get_session() should not be called for inactive statement.
+    assert(m_session);
+    return *m_session;
   }
 
   Protocol& get_protocol()
   {
-    return m_session.m_protocol;
+    return get_session().m_protocol;
   }
 
   // Async_op

cdk/mysqlx/result.cc

@@ -65,6 +65,7 @@ bool Stmt_op::do_cont()
 
   assert(ERROR != m_state);
   assert(DONE != m_state || m_op);
+  assert(m_session);
 
   try {
 
@@ -125,7 +126,7 @@ bool Stmt_op::do_cont()
           will be set to NULL so that we don't enter this branch again.
         */
 
-        m_session.deregister_stmt(m_prev_stmt);
+        m_session->deregister_stmt(m_prev_stmt);
         assert(nullptr == m_prev_stmt);
       }
 
@@ -195,6 +196,12 @@ bool Stmt_op::do_cont()
 
 bool Stmt_op::is_completed() const
 {
+  if (!m_session)
+  {
+    assert(DONE == m_state || ERROR == m_state);
+    return true;
+  }
+
   switch (m_state)
   {
   case ERROR:

cdk/mysqlx/session.cc

@@ -39,6 +39,7 @@ POP_SYS_WARNINGS_CDK
 
 #include "stmt.h"
 
+
 namespace cdk {
 namespace mysqlx {
 
@@ -739,6 +740,9 @@ void Session::close()
 void Session::register_stmt(Stmt_op *stmt)
 {
   assert(stmt);
+  assert(!stmt->m_session);
+
+  stmt->m_session = this;
 
   // Append stmt to the end of the list of active statements.
 
@@ -756,6 +760,12 @@ void Session::deregister_stmt(Stmt_op *stmt)
 {
   assert(stmt);
 
+  if (!stmt->m_session)
+    return;
+
+  assert(stmt->m_session == this);
+  stmt->m_session = nullptr;
+
   // Remove stmt from the list of active statements.
 
   if (stmt->m_next_stmt)