Global variables:

int writers = 1; /* number of writers allowed to write */
int readers = 0;  /* number of readers executing */
int writers_waiting = 0; /* number of writers waiting */
int readers_waiting = 0; /* number of readers waiting */
boolean writersPriority = true; /* true if writers have priority */

readAcquire {

  /* Everything is atomic except for the block operation */
  while (writers ==0   ||( (writers_waiting> 0) && writersPriority)) {
    readersWaiting ++;
    block;
    readersWaiting --;
  }
  readersWaiting --;
  readers++;

}

readRelease {
  readers--;
  writersPriority = !writersPriority; /* toggle writers Priority */
}

writeAcquire {
  
  /* Everything is atomic except for the block operation */
  while (writers == 0 || readers > 0 || (readers_waiting > 0 && !writersPriority)) {
    writers_waiting++;
    block;
    writers_waiting--;
  }
 
  writersWaiting--;
  writers = 0;
  
}

writeRelease {
  writers = 1;
  writersPriority = !writersPriority; /* toggle writers Priority */
}