Solving Reader-Writer Problem

I know may be i bored you with basic semaphores and semaphore problems;but I hope it will be useful for the people who are just introducing with them.

Reader Writer Problem with Semaphores:

If one process is reading an object , other processes can read it too ;but they can not write or modify this object .
Generally the case is like that:
While Writing -> Can't write or read the object
While Reading->Can read ;but can not modify the object.

Shared Data:

semaphore mutex , wrt;
int readcount;

//Initially
mutex=1 , wrt =1, readcount=0;

Writer:

wait(wrt);//wrt-- , wrt=0;
writeToFile();//...Writing is performed
signal(wrt);//wrt++ , wrt=1;

While wrt=1 the writing process can be done by other processes.
While wrt=0 the other processes can not write to the object.

The reader process is a bit more complex.

Reader:

wait(mutex);//mutex--, mutex=0
readcount++;// readcount=1
if(readcount==1)
{wait(wrt);}
signal(mutex);

readTheObject();//...Reading is performed

wait(mutex);
readcount--; // readcount=0;
if(readcount==0) //Check if the reading is performed
signal(wrt);
signal(mutex);

The codes between wait(mutex) and signal(mutex) are the places where we don't want other processes access to avoid ambiguousness.

An Example about how this code works:
1 2 3
Reader1:readcount=1,wrt=0,readcount=1 .
Reader2:readcount=2,wrt=0, readcount=0,wrt=1.
Writer: writing, writing is finished.