Difference between Semaphore and Monitor
In this article, you will learn the difference between the semaphore and monitor. But before discussing the differences, you will need to know about the semaphore and monitor.
What is Semaphore?
A semaphore is an integer variable that allows many processes in a parallel system to manage access to a common resource like a multitasking OS. It is an integer variable (S), and it is initialized with the number of resources in the system. The wait() and signal() methods are the only methods that may modify the semaphore (S) value. When one process modifies the semaphore value, other processes can't modify the semaphore value simultaneously.
Furthermore, the operating system categorizes semaphores into two types:
In Counting Semaphore, the value of semaphore S is initialized to the number of resources in the system. When a process needs to access shared resources, it calls the wait() method on the semaphore, decreasing its value by one. When the shared resource is released, it calls the signal() method, increasing the value by 1.
When the semaphore count reaches 0, it implies that the processes have used all resources. Suppose a process needs to utilize a resource when the semaphore count is 0. In that case, it performs the wait() method, and it is blocked until another process using the shared resources releases it, and the value of the semaphore increases to 1.
Semaphore has a value between 0 and 1 in binary semaphore. It's comparable to mutex lock, except that mutex is a locking method while the semaphore is a signalling method. When a process needs to access a binary semaphore resource, it uses the wait() method to decrement the semaphore's value from 1 to 0.
When the process releases the resource, it uses the signal() method to increase the semaphore value to 1. When the semaphore value is 0, and a process needs to use the resource, it uses the wait() method to block until the current process that is using the resource releases it.
The syntax of the semaphore may be used as:
Advantages and Disadvantages of Semaphore
Various advantages and disadvantages of the semaphore are as follows:
What is Monitor?
It is a synchronization technique that enables threads to mutual exclusion and the wait() for a given condition to become true. It is an abstract data type. It has a shared variable and a collection of procedures executing on the shared variable. A process may not directly access the shared data variables, and procedures are required to allow several processes to access the shared data variables simultaneously.
At any particular time, only one process may be active in a monitor. Other processes that require access to the shared variables must queue and are only granted access after the previous process releases the shared variables.
The syntax of the monitor may be used as:
Advantages and Disadvantages of Monitor
Various advantages and disadvantages of the monitor are as follows:
Main Differences between the Semaphore and Monitor
Here, you will learn the main differences between the semaphore and monitor. Some of the main differences are as follows:
Head-to-head comparison between the Semaphore and Monitor
Various head-to-head comparisons between the semaphore and monitor are as follows:
In summary, semaphore and monitor are two synchronization mechanisms. A semaphore is an integer variable that performs the wait() and signal() methods. In contrast, the monitor is an abstract data type that enables only a process to use a shared resource at a time. Monitors are simpler to implement than semaphores, and there are fewer chances of making a mistake in monitors than with semaphores.