text: // Copyright 2018-2019 Espressif Systems (Shanghai) PTE LTD
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #include <reent.h>
  
  #include "freertos/FreeRTOS.h"
  #include "freertos/task.h"
  
  static struct _reent impure_data;
  struct _reent *_global_impure_ptr = &impure_data;
  
  struct _reent *__getreent()
  {
  #if configUSE_NEWLIB_REENTRANT == 1
      /*
       * Locking mutex(only mutex, not ISR mutex) at the following three
       * state may cause OS death. So we use a extra _reent data instead
       * of task private reent data.
       * 
       * But although at the state none of "taskSCHEDULER_RUNNING",  exception
       * can cause CPU swicth context, then Locking mutex may cause OS death.
       * So we command that use ets_printf(ROM function) instead of "printf"
       * at exception and system kernal critical state.
       */
      if (xPortInIsrContext() 
          || !xTaskGetCurrentTaskHandle()
          || xTaskGetSchedulerState() != taskSCHEDULER_RUNNING)
          return &impure_data;
  
      /*
       * When scheduler starts, _global_impure_ptr = pxCurrentTCB->xNewLib_reent.
       */
  #endif
      return _global_impure_ptr;
  }
  