In esp-open-sdk function like
#ifndef MEM_H
#define MEM_H
#define os_malloc pvPortMalloc
#define os_free vPortFree
#define os_zalloc pvPortZalloc

it would appear that the OS in use is FreeRTOS (or it's commercially licensed equivalent OpenRTOS)

also function like

#include "os_type.h"
void system_set_os_print(uint8 onoff);
bool system_os_task(os_task_t task, uint8 prio, os_event_t *queue, uint8 qlen);
bool system_os_post(uint8 prio, os_signal_t sig, os_param_t par);

is these function uses FreeRTOS or any another OS mechanism please guide.