Mutex and semaphore are two synchronization mechanisms that allow multiple processes to share data without inconsistency. While both offer similar functionality, they have different applications depending on the needs of the system. In this blog post, we will explore the difference between mutex and semaphore, and when each should be used.
What is Mutex?
A Mutex is a program object that allows multiple process threads to share the same resource, such as file access. Mutexes are similar to semaphores in that they allow multiple threads to synchronize their actions. However, semaphores can have a maximum count greater than 1, whereas a Mutex can only be either locked or unlocked, with a maximum count of 1. When a Mutex is locked (acquired), it blocks other process threads from acquiring the Mutex.
The thread that locked the Mutex can unlock (release) the Mutex when it has finished using the shared resource. If the Mutex is already locked when a thread attempts to lock it, the thread will block until the Mutex is unlocked by another thread. process threads use Mutexes for various purposes, such as ensuring that only one thread is modifying a shared data structure at any given time. Mutexes can also be used to implement critical sections and monitors.
What is Semaphore?
A semaphore is a synchronization mechanism for enforcing limits on access to a resource. A semaphore maintains an internal counter that is incremented each time the semaphore is acquired and decremented each time it is released. If the counter is greater than zero, then the resource is available. If the counter is equal to zero, then the resource is unavailable. Semaphores can be used to implement policies for managing access to finite resources such as shared memory, network sockets, or disk files. Semaphores can also be used to limit the number of threads that can execute a particular section of code at any given time.
Semaphores are commonly used in systems with multiple processors to ensure that thread execution order is maintained and that critical sections are executed atomically. Semaphores can be implemented in a variety of ways, including using atomic operations, spin locks, and lock-free data structures. Semaphores are an important tool for managing access to shared resources in a concurrent system.
Difference between Mutex and Semaphore
Mutex and Semaphore are two types of objects that are used for synchronization between threads. Mutex is a shorter name for Mutual Exclusion Object. Mutexes are usually used to serialize access to a resource. A mutex object only allows one thread into a controlled section, forcing other threads which attempt to gain access to that section to wait until the first thread has exited from that section. When a second thread tries to enter the critical section, it finds the mutex is locked by the first thread.
The second thread then waits until it can acquire the lock. In this way, Mutex solves the problem of multiple threads using the same resource at the same time. A semaphore is an object that maintains a counter which indicates the number of resources currently available. When a thread wants to use one of these resources, it must first acquire a semaphore.
If there are no available resources, then the thread will be blocked until another thread releases a resource back to the semaphore. Mutexes and Semaphores serve different purposes, but they are both important in multi-threaded programming.
Mutex and semaphores are both synchronization primitives that allow multiple threads to access a shared resource without causing data corruption. However, they differ in how they achieve this goal. A mutex ensures that only one thread can access the resource at a time, while a semaphore allows multiple threads to access the resource but restricts the number of concurrent operations.