Top 10 List of Week 07

1. The Critical Section Problem
   Critical Section is the part of a program which tries to access shared resources. That resource may be any resource in a computer like a memory location, Data structure, CPU or any IO device. The critical section cannot be executed by more than one process at the same time; operating system faces the difficulties in allowing and disallowing the processes from entering the critical section. The critical section problem is used to design a set of protocols which can ensure that the Race condition among the processes will never arise.

2. Race Condition
   When more than one processes are executing the same code or accessing the same memory or any shared variable in that condition there is a possibility that the output or the value of the shared variable is wrong so for that all the processes doing the race to say that my output is correct this condition known as a race condition. Several processes access and process the manipulations over the same data concurrently, then the outcome depends on the particular order in which the access takes place. A race condition is a situation that may occur inside a critical section. This happens when the result of multiple thread execution in the critical section differs according to the order in which the threads execute.

3. Dining Philosopher Problem
   The Dining Philosopher Problem states that K philosophers seated around a circular table with one chopstick between each pair of philosophers. There is one chopstick between each philosopher. A philosopher may eat if he can pickup the two chopsticks adjacent to him. One chopstick may be picked up by any one of its adjacent followers but not both.

4. Fun with Concurrency Problems
   This blog shows us about a problem about concurrency, specifically about race condition caused by a Singleton pattern with lazy initialization. Interesting, right?

5. Semaphores in Process Synchronization
   Semaphore was proposed by Dijkstra in 1965 which is a very significant technique to manage concurrent processes by using a simple integer value, which is known as a semaphore. Semaphore is simply a variable that is non-negative and shared between threads. This variable is used to solve the critical section problem and to achieve process synchronization in the multiprocessing environment.

6. Introduction of Deadlock in Operating System
   Deadlock is a situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process. Consider an example when two trains are coming toward each other on the same track and there is only one track, none of the trains can move once they are in front of each other. A similar situation occurs in operating systems when there are two or more processes that hold some resources and wait for resources held by other(s). For example, in the below diagram, Process 1 is holding Resource 1 and waiting for resource 2 which is acquired by process 2, and process 2 is waiting for resource 1.

7. Mutex vs Semaphore
   What is the difference between a mutex and a semaphore? When should you use a mutex and when should you use a semaphore? As per operating system terminology, mutexes and semaphores are kernel resources that provide synchronization services (also called synchronization primitives). This blog illustrate with examples to understand these concepts well, rather than following the usual OS textual description.

8. Linux Sticky Bit Concept Explained with Examples
   Think of a scenario where you create a Linux directory that can be used by all the users of the Linux system for creating files. Users can create, delete or rename files according to their convenience in this directory. For all those who think that why would such a directory be created? There exists, for example, /tmp directory in the Linux system that can be used by different Linux users to create temporary files. A Sticky bit is a permission bit that is set on a file or a directory that lets only the owner of the file/directory or the root user to delete or rename the file. No other user is given privileges to delete the file created by some other user. A Sticky bit is a permission bit that is set on a file or a directory that lets only the owner of the file/directory or the root user to delete or rename the file. No other user is given privileges to delete the file created by some other user.

9. Readers-Writers Problem
   The readers-writers problem relates to an object such as a file that is shared between multiple processes. Some of these processes are readers i.e. they only want to read the data from the object and some of the processes are writers i.e. they want to write into the object. The readers-writers problem is used to manage synchronization so that there are no problems with the object data. For example - If two readers access the object at the same time there is no problem. However if two writers or a reader and writer access the object at the same time, there may be problems. To solve this situation, a writer should get exclusive access to an object i.e. when a writer is accessing the object, no reader or writer may access it. However, multiple readers can access the object at the same time.

10. Bounded Buffer Problem
    Bounded buffer problem, which is also called producer consumer problem, is one of the classic problems of synchronization. There is a buffer of n slots and each slot is capable of storing one unit of data. There are two processes running, namely, producer and consumer, which are operating on the buffer. A producer tries to insert data into an empty slot of the buffer. A consumer tries to remove data from a filled slot in the buffer. As you might have guessed by now, those two processes won’t produce the expected output if they are being executed concurrently. There needs to be a way to make the producer and consumer work in an independent manner.