I have updated apache-2.4.29 to apache-2.4.37 but still I am not able to graceful shutdown in debug mode.
Can you please tell me how should achieve it. ? or let me know the function which I should call for proper graceful shutdown.
Each MPM (event, worker, process) has it's own signaling architecture between parent and child processes.
You will need to review the behavior of the child signal handler specific to the MPM you want to control.
Quoting the doc above; "You will notice many httpd executables running on your system, but you should not send signals to any of them except the parent, whose pid is in the PidFile. That is to say you shouldn't ever need to send signals to any process except the parent. There are four signals that you can send the parent: TERM, USR1, HUP, andWINCH, which will be described in a moment."
So what you seek to do is, effectively undocumented/unsupported. Debug mode is not a supported operating mode, as I mentioned earlier.