Difference between mutual exclusion and synchronization?

concurrency synchronization mutual-exclusion
Tanya picture Tanya · Apr 11, 2012 · Viewed 18.9k times · Source

What is the difference between above two?

This question came to my mind because I found that

  1. Monitors and locks provide mutual exclusion

  2. Semaphores and conditional variables provide synchronization

Is this true?

Also while searching I found this article

Any clarifications please.

Answer

Alok Save picture Alok Save · Apr 11, 2012

Mutual exclusion means that only a single thread should be able to access the shared resource at any given point of time. This avoids the race conditions between threads acquireing the resource. Monitors and Locks provide the functionality to do so.

Synchronization means that you synchronize/order the access of multiple threads to the shared resource.
Consider the example:
If you have two threads, Thread 1 & Thread 2.
Thread 1 and Thread 2 execute in parallel but before Thread 1 can execute say a statement A in its sequence it is a must that Thread 2 should execute a statement B in its sequence. What you need here is synchronization. A semaphore provides that. You put a semapohore wait before the statement A in Thread 1 and you post to the semaphore after statement B in Thread 2.
This ensures the synchronization you need.

Related questions

How do synchronized static methods work in Java and can I use it for loading Hibernate entities?

If I have a util class with static methods that will call Hibernate functions to accomplish basic data access. I am wondering if making the method synchronized is the right approach to ensure thread-safety. I want this to prevent access …

Read More
How to use the CancellationToken property?

Compared to the preceding code for class RulyCanceler, I wanted to run code using CancellationTokenSource. How do I use it as mentioned in Cancellation Tokens, i.e. without throwing/catching an exception? Can I use the IsCancellationRequested property? I attempted …

Read More
Synchronization vs Lock

java.util.concurrent API provides a class called as Lock, which would basically serialize the control in order to access the critical resource. It gives method such as park() and unpark(). We can do similar things if we can use …

Read More