C program for reader writer problem

A Critical Section is a code segment that accesses shared variables and has to be executed as an atomic action. It means that in a group of cooperating processes, at a given point of time, only one process must be executing its critical section. If any other process also wants to execute its critical section, it must wait until the first one finishes.

Out of a group of cooperating processes, only one process can be in its critical section at a given point of time. If no process is in its critical section, and if one or more threads want to execute their critical section then any one of these threads must be allowed to get into its critical section. After a process makes a request for getting into its critical section, there is a limit for how many other processes can get into their critical section, before this process's request is granted.

So after the limit is reached, system must grant the process permission to get into its critical section. In Software Approach, Some specific Algorithm approach is used to maintain synchronization of the data. Like in Approach One or Approach Two, for a number of two process, a temporary variable like turn or boolean variable flag value is used to store the data.

This does not satisfy all the Critical Section requirements. It uses two variables in the Entry Section so as to maintain consistency, like Flag boolean variable and Turn variable storing the process states.

Locking part is done in the Entry Section, so that only one process is allowed to enter into the Critical Section, after it complete its execution, the process is moved to the Exit Section, where Unlock Operation is done so that another process in the Lock Section can repeat this process of Execution. As the hardware solution is not easy to implement for everyone, a strict software approach called Mutex Locks was introduced. In this approach, in the entry section of code, a LOCK is acquired over the critical resources modified and used inside critical section, and in the exit section that LOCK is released.

As the resource is locked while a process executes its critical section hence no other process can access it. The Overflow Blog. Podcast Making Agile work for data science.

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Question feed. Stack Overflow works best with JavaScript enabled. Obviously, if two readers access the shared data simultaneously, no adverse effects will result. However, if a writer and some other process either a reader or a writer access the database simultaneously, chaos may ensue.

To ensure that these difficulties do not arise, we require that the writers have exclusive access to the shared database while writing to the database. This synchronization problem is referred to as the readers-writers problem. December 17, December 26, Your email address will not be published.