Threads And Concurrency Questions Long
The dining philosophers problem is a classic synchronization problem in computer science that illustrates the challenges of resource allocation and concurrency control in a multi-threaded environment. It was introduced by Edsger Dijkstra in 1965 as an analogy to the problem of deadlock in operating systems.
The problem is as follows: There are five philosophers sitting around a circular table, and each philosopher alternates between thinking and eating. There is a bowl of rice in the center of the table, and each philosopher needs two chopsticks to eat. However, there are only five chopsticks available, one between each pair of adjacent philosophers.
The challenge is to design a solution that allows the philosophers to eat without causing deadlock or starvation. Deadlock occurs when all philosophers pick up their left chopstick simultaneously and then wait indefinitely for their right chopstick, resulting in a circular dependency. Starvation occurs when a philosopher is unable to acquire both chopsticks and is constantly bypassed by others.
To solve this problem, various synchronization techniques can be employed. One common solution is to use a semaphore or mutex to represent each chopstick. Each philosopher must acquire both chopsticks before eating and release them afterward. However, to prevent deadlock, a rule can be imposed that philosophers can only pick up chopsticks if both are available. This ensures that at least one philosopher can always eat, breaking the circular dependency.
Another solution is to introduce a waiter or arbiter who controls the allocation of chopsticks. The waiter ensures that no more than four philosophers are simultaneously picking up chopsticks, preventing deadlock. The waiter can use various strategies, such as assigning a priority to philosophers or implementing a queue system, to ensure fairness and prevent starvation.
Additionally, techniques like resource hierarchy, where philosophers are assigned a unique identifier and always pick up chopsticks in a specific order, can be used to prevent deadlock. This ensures that there is no circular dependency and that each philosopher can eventually acquire both chopsticks.
Overall, the dining philosophers problem highlights the challenges of resource allocation and concurrency control in multi-threaded systems. It requires careful design and synchronization techniques to ensure that all philosophers can eat without deadlock or starvation.