C / C++ / MFC

typepdef volatile int semaphore;

void semaphore_inc (semaphore* sem) 
{
   disable context switcher;
   while (*sem != 0)
   {
      enable context switcher;
      sleep(1);
      disable context switcher;
   }
   *sem++;
   enable context switcher;
}

void semaphore_dec (semaphore* sem)
{
   disable context switcher;
   *sem--;
   enable context switcher;
}

semaphore sem = 0;

void taskACall (void)
{
   semaphore_inc(&sem);
   .... // do task A code
   semaphore_dec(&sem);
}

void taskBCall (void)
{
   semaphore_inc(&sem);
   .... // do task B code
   semaphore_dec(&sem);
}

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);
}