Graphical Representation of Allocated Resources (GRAR)

In the realm of computer science, the concept of deadlocks can pose a significant challenge in multiprocessing systems. One tool used to combat this issue is the Resource Allocation Graph (RAG), a visual representation that helps detect deadlocks by analysing the relationships between processes and resources.

The RAG, as introduced by R. Subramanian in his work "Deadlock Detection using Resource Allocation Graph", provides a clear picture of how resources are allocated and requested among different processes. For instance, consider a system where Process P1 is waiting for Resource R1, currently held by Process P2. Similarly, Process P2 is waiting for Resource R3, which is in the possession of Process P3. Meanwhile, Process P3 is waiting for an instance of Resource R2, but all available instances are held by both P1 and P2.

This setup creates a potential cycle in the RAG, where each process is waiting for a resource held by the next process in the cycle. If the RAG contains a cycle and there is only one instance per resource type, it indicates a deadlock. However, if there are several instances per resource type, it suggests the possibility of a deadlock.

In such a scenario, if the RAG contains a cycle, it means that all processes are blocked and cannot proceed. This situation is known as a System in Deadlock, where no progress can be made until at least one process in the cycle can complete and release resources, allowing the remaining processes to proceed.

On the other hand, if the RAG contains no cycles, there is no deadlock. This means that every process is either running or waiting for a resource that will become available in the future. The RAG, therefore, serves as a valuable tool in preventing and resolving deadlocks, ensuring the smooth operation of multiprocessing systems.