Binary Semaphore

A binary semaphore is a semaphore with an integer value which can range between 0 and 1.
Let ‘S’ be a counting semaphore. To implement the binary semaphore we need following the structure of data.

Binary Semaphores S1, S2;
int C;
Initially S1 = 1, S2 = 0 and the value of C is set to the initial value of the counting semaphore ‘S’.
Then the wait operation of the binary semaphore can be implemented as follows.
Wait (S1)
C--;
if (C < 0)
{
 Signal (S1);
 Wait (S2);
} 
Signal (S1); 

The signal operation of the binary semaphore can be implemented as follows:

Wait (S1);
C++;
if (C <=0)
Signal (S2);
Else
Signal (S1);