This document discusses semaphores as a software solution to the critical section problem in operating systems. It defines semaphores as integer variables used with two atomic operations, wait() and signal(), to synchronize processes. There are two main types: counting semaphores, which can have any integer value representing available resources, and binary semaphores, which are restricted to values of 0 and 1. Semaphores solve synchronization issues like the critical section problem, order of execution, and resource management in operating systems.

1. Operating System
Concepts
Instructor Name: Muhammad Asif
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2. Quick Recap of Previous Lecture
• Critical Section Problem
• Condition for the Solution to the Critical Section Problem
• Race Condition
• Peterson’s Solution
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3. Today’s Outlines
• Software solution to the Critical Section Problem
• Semaphore
• Wait ( )
• Signal ( )
• Types of Semaphore
• Counting semaphore
• Binary semaphore
• Advantages of semaphore
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4. Semaphore
• Semaphore is an integer variables that are used to solve the
critical section problem by using two atomic operations,
• That are used for process synchronization:
• Wait()
• Signal ()
• Always initialize the variable with 1 if solving the Critical
Section Problem:
int S = 1;
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5. Semaphore
do{
wait ( S ); // ftn call
// critical section // enter in its critical section
Signal ( S ); // ftn call
// termination section
• }while(true); 5

6. Semaphore
Where int S = 1;
do{
wait ( S ); // ftn call
// critical section // enter in its critical section
Signal ( S ); // ftn call
// termination section
}while(true); 6

7. Types of Semaphores
• There are two main types of semaphores i.e. counting
semaphores and binary semaphores. Details about these are
given as follows:
• Counting Semaphores
• Binary Semaphores
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8. Semaphore
• Binary Semaphores
• The binary semaphores are like counting semaphores but their
value is restricted to 0 and 1.
• The wait operation only works when the semaphore is 1 and the
signal operation succeeds when semaphore is 0.
• It is sometimes easier to implement binary semaphores than
counting semaphores.
• Counting Semaphores:
• These are integer value semaphores and have an unrestricted value
domain.
• These semaphores are used to coordinate the resource access,
where the semaphore count is the number of available resources.
• If the resources are added, semaphore count automatically
incremented and if the resources are removed, the count is
decremented.
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9. Advantages of Semaphores
• Semaphore is used to solve different problems like:
• Critical Section Problem
• Order of execution among the processes
• Resource Management
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10. Any Questions?
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