![]() On the other hands, Mutex allows multiple program threads to access a single shared resource but one at a time. Semaphore allows multiple program threads to access the finite instance of resources.Semaphore is typically an integer variable whereas, mutex is an object.On the other hands, the mutex is a locking mechanism, as to acquire a resource, a process needs to lock the mutex object and while releasing a resource process has to unlock mutex object. Semaphore is a signalling mechanism as wait() and signal() operation performed on semaphore variable indicates whether a process is acquiring the resource or releasing the resource.Key Differences Between Semaphore and Mutex If the mutex object is already locked, the process desiring to acquire the lock on mutex object has to wait and is queued up by the system till the mutex object is unlocked. Meanwhile, a process has acquired the lock on mutex object no other thread/process can access that resource. Then the next process is allowed to acquire the lock on mutex object. ![]() Whenever the program thread wants to use the resource it occupies lock on mutex object, utilizes the resource and after use, it releases the lock on mutex object. The system creates the mutex object with a unique name or ID. When a program starts it request the system to creates a mutex object for a given resource. The mutex object allows the multiple program threads to use the same resource but one at a time not simultaneously. From the term mutual exclusion, we can understand that only one process at a time can access the given resource. Mutual Exclusion Object is shortly termed as Mutex. If the value of semaphore is 0 and a process want to access the resource it performs wait() operation and block itself till the current process utilizing the resources releases the resource. ![]() When it releases the resource, it performs a signal() operation on the semaphore and increments its value to 1. In binary semaphore, if a process wants to access the resource it performs wait() operation on the semaphore and decrements the value of semaphore from 1 to 0. It is similar to mutex lock, but mutex is a locking mechanism whereas, the semaphore is a signalling mechanism. In Binary semaphore, the value of semaphore ranges between 0 and 1. If a process need to use a resource when semaphore count is 0, it executes wait() and get blocked until the value of semaphore becomes greater than 0. When the semaphore count goes to 0, it means all resources are occupied by the processes. When it releases the resource, it performs signal() operation on the semaphore and increments the value of semaphore by one. Whenever a process wants to access the resource it performs wait() operation on the semaphore and decrements the value of semaphore by one. In Counting Semaphore, the semaphore S value is initialized to the number of resources present in the system. Semaphore are distinguished by the operating system in two categories Counting semaphores and Binary semaphore. It means that when a process is modifying the value of the semaphore, no other process can simultaneously modify the value of the semaphore. ![]() The wait() and signal() operation modify the value of the semaphore indivisibly. Semaphore is typically an integer variable S that is initialized to the number of resources present in the system and the value of semaphore can be modified only by two functions wait() and signal() apart from initialization. Semaphore is a process synchronization tool. If a mutex object is already locked, the process requesting for resources waits and queued by the system till lock is released. If all resources are being used, the process requesting for resource performs wait() operation and block itself till semaphore count become greater than one. Mutex object is locked or unlocked by the process requesting or releasing the resource. Semaphore value is modified using wait() and signal() operation. Semaphore can be categorized into counting semaphore and binary semaphore. Mutex object lock is released only by the process that has acquired the lock on it. Semaphore value can be changed by any process acquiring or releasing the resource. ![]() Mutex allow multiple program thread to access a single resource but not simultaneously. Semaphore allow multiple program threads to access a finite instance of resources. There are some more differences between semaphore and mutex, let us discuss them with the help of comparison chart shown below. processes perform wait() and signal() operation to indicate whether they are acquiring or releasing the resource, while Mutex is locking mechanism, the process has to acquire the lock on mutex object if it wants to acquire the resource. The basic difference between semaphore and mutex is that semaphore is a signalling mechanism i.e. ![]()
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