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| What is Semaphore in OS |
Semaphore in OS
A Semaphore is a regular integer value, and it cannot have a negative value. Semaphores in OS used to resolve the problems of critical section and synchronize the processes by using operations. Semaphore has two operations that are wait and signal.
Wait
The wait operation of semaphore is used to decrease the positive value
of its argument S. If the value of argument S is zero or negative, then no
actin is taken.
wait(S)
{
while (S<=0);
S--;
}
Signal
The signal operation of semaphore is used to increase the value of its
parameter S.
signal(S)
{
S++;
}
Semaphores are utilized to create critical sections, segments of code that require exclusive execution by one process at a time. They facilitate the coordination of process access to shared resources like memory or I/O devices.
Types of Semaphores
Types of semaphores are :
- Counting semaphores
- Binary semaphores
These are described in more detail as follows:
Counting semaphores
Counting semaphore has value in whole numbers and unlimited value domain. To arrange the resource access these semaphores are used.
When resources are added, the
semaphore count is automatically increased; when resources are removed, the
count is automatically decreased.
Binary semaphores
Binary semaphores are semaphores that value is 0 or 1. If it
value is equal to 1 then wait operation is perform and if value is 0 then
signal operation perform.
Advantages of Semaphores
- Offers a straightforward and efficient method for synchronizing processes
- Facilitates coordination among multiple processes
- Offers a versatile and resilient approach to handling shared resources
- Enables the implementation of critical sections within a program
- Helps prevent race conditions and ensures smooth execution.
- A single process can enter in critical section.
- Semaphores synchronization techniques are more effective than some others because they strictly adhere to the mutual exclusion principle.
Disadvantages of Semaphores:
- May cause performance decline due to the overhead from wait and signal operations.
- Incorrect use can result in deadlock.
- Improper usage may lead to program performance issues.
- Debugging and maintenance can be challenging.
- Incorrect application may cause race conditions and synchronization problems.
- Vulnerable to specific attacks, like denial of service attacks.
