struct Semaphore
{
    int value; // processes that can enter in the critical section simultaneously. 
    queue type L; // L contains set of processes which get blocked 
}
Down (Semaphore S)
{
    S.value = S.value - 1; //semaphore's value will get decreased when a new 
    //process enter in the critical section 
    if (S.value< 0)
    {
        put_process(PCB) in L; //if the value is negative then 
        //the process will get into the blocked state.
        Sleep(); 
    }
    else
        return;
}
up (Semaphore s)
{
    S.value = S.value+1; //semaphore value will get increased when 
    //it makes an exit from the critical section. 
    if(S.value<=0)
    {
        select a process from L; //if the value of semaphore is positive 
        //then wake one of the processes in the blocked queue. 
        wake-up();
    }
    }
}