Semaphore in task with queue on ESP32 idf 5.0

Kernel
1 
void vTaskDisplay( void * pvParameters )
{
   while(1)
   {
      // Queue receive, wait 10
      if( xQueueReceive( displayQueue, &cmd, ( TickType_t ) 10 ) == pdPASS )
      {
         if (SHOW == cmd) {
           printf("db 1 - begin\n");
           xSemaphoreTake(s_lock, portMAX_DELAY);
           flash_db_operation();
           xSemaphoreGive(s_lock);
           printf("db 1 - end\n");
         }
      }

      printf("display_tick()\n");
      display_tick();
   }
}

I have the simplified my code, but is does basically as the code above.
My expected outcome would be:
db 1 - begin
db 1 - end
display_tick()

But sometimes I see:
db 1 - begin
display_tick()
display_tick()
db 1 - end

So it seems like the task is waiting for the semaphore, but then runs again.
Maybe I have totally misunderstood something, but I would expect the task to be blocked, until the semaphore is given. It is like the task is fork’ed or something.

2

According to your example code it should be impossible to get a
db 1 - begin
display_tick()
display_tick()
db 1 - end
sequence.
I assume you verified that there is only 1 task running the code.
Did you also verify that there is no stack overflow or an configASSERT ?
There must a fatal problem making the code running wild.
Alternatively you could comment out flash_db_operation and put in e.g. a vTaskDelay to simulate the flash operation to narrow down where the application gets corrupted.

1 Like
3

Do not rely on printf() to provide accurate output.

Also, could it be the case that you have spawned two instances of your display task, as Hartmut suggested?

4

@hs2 and @RAc You where correct, my Init function was called twice, and therefore xTaskCreate was called two times. :slight_smile:

5

Thanks for reporting back!