Difference Between Counting and Binary Semaphores
Last Updated :
03 Oct, 2024
Semaphores are signaling devices used in computer systems to facilitate the control of access to common resources. For it is employed to prevent several processes (or programs) from conflicting with one another when all of them are competing for the same resource. There are two main types of semaphores: Counting semaphores and binary semaphores. While both are access-related, the function is not the same, that is access control relates to how a particular resource is being accessed. In this article, we will discuss what is the main difference between counting semaphores and binary semaphores.
What is Counting Semaphore?
A counting semaphore is a type of synchronization where we are using an integer value of more than one. It enables several processes to utilize a limited number of objects of a shared item. To value of the semaphore can be increased or decreased based on whether a process has released the resource or has acquired it.
Advantages of Counting Semaphore
- Multiple Resource Access: Thus, it supports multiple access and can be used profitably with resources of multiple instances.
- Flexibility: The semaphore value can be access-related of any number of available resources.
- Scalability: It does scale well in systems that involve many processes or threads that will all need to access shared resources at the same time.
Disadvantages of Counting Semaphore
- Complexity: Managing counting semaphores itself is relatively easier; however, it becomes a little complicated when there are many shared resources.
- Potential for Misuse: However, counting semaphores comes with problems like deadlock or starvation when not well managed.
What is Binary Semaphore?
A binary semaphore, also known as a mutex or mutual exclusion semaphore, is a simpler version of a semaphore that only has two states: It can take one of two gross forms namely 0 form which means that something is not available, and the 1 form which means that the constituent is available. It is mainly used to ensure that at any one particular time, a representative processor or a thread can access a shared resource.
Advantages of Binary Semaphore
- Simple Implementation: In implementation, binary semaphores are less complex than counting semaphores, and this makes their management easy as well.
- Efficient for Mutual Exclusion: They are particularly applicable in solutions to mutual exclusion where only a single resource can be accessed at a given time.
- Low Overhead: Binary semaphores work in two states and therefore, they allow little overhead compared to counting semaphores.
Disadvantages of Binary Semaphore
- Limited Functionality: It cannot support multiple resources to be accessed together; this reduces their
- Deadlock Risk: Abuse of binary semaphores may also result in a deadlock condition.
Difference Between Counting and Binary Semaphores
Criteria | Binary Semaphore | Counting Semaphore |
| Definition | A Binary Semaphore is a semaphore whose integer value range over 0 and 1. | A counting semaphore is a semaphore that has multiple values of the counter. The value can range over an unrestricted domain. |
| Structure Implementation | typedef struct {
int semaphore_variable;
}binary_semaphore; | typedef struct {
int semaphore_variable;
Queue list; //A queue to store the list of task
}counting_semaphore; |
| Representation | 0 means that a process or a thread is accessing the critical section, other process should wait for it to exit the critical section. 1 represents the critical section is free. | The value can range from 0 to N, where N is the number of process or thread that has to enter the critical section. |
| Mutual Exclusion | Yes, it guarantees mutual exclusion, since just one process or thread can enter the critical section at a time. | No, it doesn't guarantees mutual exclusion, since more than one process or thread can enter the critical section at a time. |
| Bounded wait | No, it doesn't guarantees bounded wait, as only one process can enter the critical section, and there is no limit on how long the process can exist in the critical section, making another process to starve. | Yes, it guarantees bounded wait, since it maintains a list of all the process or threads, using a queue, and each process or thread get a chance to enter the critical section once. So no question of starvation. |
| Starvation | No waiting queue is present then FCFS (first come first serve) is not followed so,starvation is possible and busy wait present | Waiting queue is present then FCFS (first come first serve) is followed so,no starvation hence no busy wait. |
| Number of instance | Used only for a single instance of resource type R.it can be usedonly for 2 processes. | Used for any number of instance of resource of type R.it can be used for any number of processes. |
Conclusion
All in all, counting semaphores enable handling resources, rendering them appropriate for systems where many processes share resources. In turn, binary semaphores are best used in easier mutual exclusion issues when only one process can work with the resource simultaneously. In view of this, the appropriateness of this counting and the binary semaphores depends on the need of the system and the extent of the resource protection required.
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