Readers Writers: Address reader, writer starvation

int readcount;                // init to 0; number of readers currently accessing resource

resource = S(1);           // controls access (read/write) to the resource
rmutex = S(1);             // for syncing changes to shared variable readcount
serviceQueue = S(1);       // FAIRNESS: preserves ordering of requests (signaling must be FIFO)

//READER
reader() {
<ENTRY Section>
  serviceQueue.P();           // wait in line to be serviced
  rmutex.P();                 // request exclusive access to readcount
  readcount++;                // update count of active readers
  if (readcount == 1)         // if I am the first reader
    resource.P();             // request resource access for readers (writers blocked)
  serviceQueue.V();           // let next in line be serviced
  rmutex.V();                 // release access to readcount
    
<CRITICAL Section>
//reading is performed
    
<EXIT Section>
  rmutex.P();                 // request exclusive access to readcount
  readcount--;                // update count of active readers
  if (readcount == 0)         // if there are no readers left
    resource.V();             // release resource access for all
  rmutex.V();                 // release access to readcount
}

//WRITER
writer() {
<ENTRY Section>
  serviceQueue.P();           // wait in line to be serviced
  resource.P();               // request exclusive access to resource
  serviceQueue.V();           // let next in line be serviced
    
<CRITICAL Section>
// writing is performed
    
<EXIT Section>
  resource.V();               // release resource access for next reader/writer
}

Taken from: https://en.wikipedia.org/wiki/Readers%E2%80%93writers_problem

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