pseudocode.txt

Using semaphores in FIFO priority, without the semaphore.h librabry.

//*********************SEMAPHORE FIFO PSEUDOCODE*********
struct Semaphore {
  int value = 1;
  Queue *Q = new Queue();
  void sem_init(int data){
    value=data;
  }
  void sem_wait(int pid){
    value--;
    if(value<0){
      Q->push(pid);
      block();
    }
  }
  void sem_post(){
    value++;
    if(value<=0){
      int pid=Q.front();
      Q.pop();
      wakeup(pid);
    }
  }
}
//*********************************************************

//The code submitted uses the semaphore librabry, so the pseudocode provides FIFO implementation of semaphores


INITIALIZATION:
begin: semaphore(1)
finish: semaphore(1)
writer_wait: semaphore(0)
reader_enter: int(0)
reader_exit: int(0)
writer_waiting: bool(false)

READER function pseudocode:
void *reader(void* id){
  //ENTRY SECTION
  begin.wait()
  reader_enter+=1
  begin.signal()

  //CRITICAL SECTION
  Read DATA

  //EXIT SECTION
  finish.wait()
  reader_exit+=1
  if(writer_waiting==true && reader_enter==reader_exit)
  then writer_wait.signal()
  finish.signal()
}

WRITER function pseudocode:
void *writer(void* id){
  //ENTRY SECTION
  begin.wait()
  finish.wait()
  if(reader_enter==reader_exit)
  then
    finish.signal()
  else{
    writer_waiting=true
    finish.signal()
    writer_wait.wait()  
    writer_waiting=false
  }

  //CRITICAL SECTION
  Process and Modify Data

  //EXIT SECTION
  begin.signal()
}