Threading Simplified: Part Twelve (Mutex)

Let’s start by putting some questions to understand the concepts.

What is Mutex in Multithreading and how is it different to lock?

Mutex stands for Mutual Exclusion and can be used for inter-process synchronization. Mutex works similarly to lock except that it’s an operating system level lock and hence can be used to lock across processes. On the contrary lock only works across threads in an AppDpmain of a process.

Mutex object can also be passed as a method parameter unlike lock.

Why Mutex is required?

Mutex can be used in cases when we want to make sure that any piece of code if locked, should not be accessed across processes. We can also use Mutex to check if another instance of the application using the same Mutex is running or not.

What is unnamed and named Mutex?

Unnamed mutex is a mutex when you don’t specify its name while creation. Unnamed mutex works across App Domains in a process.

Whereas named mutex has a bigger scope and it works across processes in an operating system.

Does lock and unnamed Mutex have similar locking scope?

No. Lock works across threads in an App Domain whereas unnamed mutex works across App domains in a process.

How to use Mutex in an application?

Mutex can be activated by WaitOne method and can be released by ReleaseMutex.

Another way to release Mutex is to close or release the mutex variable.

Similar to lock, Mutex can be released only by the thread which has activated it and not by any other running threads.

Let’s understand this by simple example.

Let’s first see an example by which we can determine that another instance of the program is running or not.

To test this, execute the below code in two different projects one after another, the later one should print “Already running”. The reason is first instance will create Mutex of name “ThreadingDemo” and hence it won’t allow another instance or process to create the same Mutex as it’s already present.

It also demonstrates that Mutex works cross processes.