source: CIVL/examples/concurrency/readerWriter.cvl@ bb03188

/**
 * This program implements the reader-writer problem.
 * The program deals with situations in which many threads must 
 * access the same shared memory at one time, some reading and some writing, 
 * with the natural constraint that no process may access the share for reading 
 * or writing while another process is in the act of writing to it. 
 * (In particular, it is allowed for two or more readers to access the share at the same time.)
 */
#include<civlc.cvh>

$input int NREADER = 3;
$input int NWRITER = 3;
int writeLock = 0;
int readLock = 0;
int writeCount = 0;
int readCount = 0;

void reader(int rid){
    while($true){
        $when(writeLock == 0) {
          $atomic {
            readLock = 1;
            readCount++;
          }
        }
        // reading
        $assert(writeCount == 0);
        readCount--;
        $atomic{
            if(readCount == 0)
                readLock = 0;
        }
    }
}

void writer(int wid){
    while($true){
        $when(writeLock == 0 && readLock == 0) writeLock = 1;
        $assert(readCount == 0  && writeCount == 0);
        writeCount++;
        // writing
        $assert(readCount == 0 && writeCount == 1);
        writeCount--;
        writeLock = 0;
    }
}

void main(){
    $proc readers[NREADER];
    $proc writers[NWRITER];
    
    for(int i = 0; i < NWRITER; i++){
        writers[i] = $spawn writer(i);
    }
    for(int i = 0; i < NREADER; i++){
        readers[i] = $spawn reader(i);
    }
    $waitall(readers, NREADER);
    $waitall(writers, NWRITER);
}