C / C++ / MFC

while(1) 
{
  count ++;
  if (count == 5)
  {
     task B be called
  }
  if (count == 10) 
  {
    count = 0;
    task A be called.
  }
}

  enum lock_state {ABoutofLockArea = 0, AinLockAreaBnormal, AinLockAreaBwaiting,  BinLockAreaAnormal, BinLockAreaAwaiting};
   
  enum lock_state state = 0;

/* MODIFIED WORK LOOP */

  while (1){
    if (count == 5)
    {
        if (state == AinLockAreaBwaiting) TaskA is called // no point calling taskB its waiting
         else task B be called
     }
     if (count == 10) 
     {
       count = 0;
       if (state == BinLockAreaAwaiting) TaskB is called // no point calling taskA its waiting
         else task A be called.
     }
   }

/* HERE ARE YOUR STATE CHANGE FUNCTIONS */

void taskA_EnterlockArea(void)
{
   if (state == BinLockAreaAnormal) state = BinLockAreaAwaiting;  // B already in there A must wait
      else state = AinLockAreaBnormal  // B is not there so A can enter
}

void taskA_LeavinglockArea(void)
{
   if (state == AinLockAreaBwaiting) state = BinLockAreaAnormal; // B is waiting it can now enter, A goes back to normal
     else state = ABoutofLockArea;   // Otherwise no one is in the lock area     
}

void taskB_EnterlockArea(void)
{
  if (state == AinLockAreaBnormal) state = AinLockAreaBwaiting;  // A already in there B must wait
      else state = BinLockAreaAnormal   // A is not there so B can enter
}

void taskB_LeavinglockArea(void)
{
   if (state == BinLockAreaAwaiting) state = AinLockAreaBnormal; // A is waiting it can now enter, B will go back to normal
     else state = ABoutofLockArea;   // Otherwise no one is in the lock area 
}

//task A: 
if (rcvd == true)  
{
  read rcv_buffer
   ...
  rcvd = false;
}

//task B:
dataCB(int ch_id, char *buf, int len, char stat)
{
  rcvd = true;
  if((rcvd == false) 
   {
      receivenotify(chid, rcv_buffer, sizeof(rcv_buffer), dataCB,0);
   }
}

rcvd = true;
if((rcvd == false)
{
    // this code is never executed
    receivenotify(chid, rcv_buffer, sizeof(rcv_buffer), dataCB,0);
}

// This code assumes you have a device context for you display window which you will pass in. 
// You get that from GetDC from BeginPaint depending where you are using this

// It is also relying that your font name is "Bravura" if it isn't change it to what you called it as the facename

#include <tchar.h>    // I don't know if your text is unicode or ansi this gets the string  copy around issue
BOOL SetFontToDC(HDC Dc)
{  
   LOGFONT lf = {0 };
   HANDLE TTFHandle;
   lf.lfHeight = -16; 	// This is the font height .. negative means absolute height required no adjusting
   lf.lfWeight = FW_NORMAL; // Set font weight .. piles of options here bold, extra bold etc
   lf.lfOutPrecision = OUT_TT_ONLY_PRECIS; // Tells windows you want TTF font
   _tcscpy_s(lf.lfFaceName, LF_FACESIZE, _T("Bravura")); // Copy the facename .. that is the name you called your font
   TTFHandle = CreateFontIndirect(&lf);	 // Tell windows to load a logical font for you (indirect aka automated no asks or prompts)
   if (TTFHandle != INVALID_HANDLE_VALUE) // If the create worked
   {
      SelectObject(Dc, TTFHandle);    // Select the font to the Screen DC .. any text to that DC will display in that font
      return TRUE;                    // Return success
    }
    return FALSE;                      // Return failure
}