If you havn't get your answer then you can try following code. Try to compare with above given code.
semaphore mutex = 1; // Controls access to the reader count
semaphore db = 1; // Controls access to the database
int reader_count; // The number of reading processes accessing the data
Reader()
{
while (TRUE) { // loop forever
down(&mutex); // gain access to reader_count
reader_count = reader_count + 1; // increment the reader_count
if (reader_count == 1)
down(&db); // if this is the first process to read the database,
// a down on db is executed to prevent access to the
// database by a writing process
up(&mutex); // allow other processes to access reader_count
read_db(); // read the database
down(&mutex); // gain access to reader_count
reader_count = reader_count - 1; // decrement reader_count
if (reader_count == 0)
up(&db); // if there are no more processes reading from the
// database, allow writing process to access the data
up(&mutex); // allow other processes to access reader_countuse_data();
// use the data read from the database (non-critical)
}
Writer()
{
while (TRUE) { // loop forever
create_data(); // create data to enter into database (non-critical)
down(&db); // gain access to the database
write_db(); // write information to the database
up(&db); // release exclusive access to the database
}