Circular Wait

"Circular Wait" is one of the four necessary conditions for a deadlock to occur in a system. This condition describes a situation where a closed chain of two or more processes or threads exists, with each process waiting for a resource held by the next process in the chain.

Explanation and Example

Definition

A Circular Wait occurs when there is a chain of processes, where each process holds a resource and simultaneously waits for a resource held by another process in the chain. This leads to a cyclic dependency and ultimately a deadlock, as none of the processes can proceed until the other releases its resource.

Example

Consider a chain of four processes $P_1, P_2, P_3, P_4$ and four resources $R_1, R_2, R_3, R_4$ :

$P_1$ holds $R_1$ and waits for $R_2$ , which is held by $P_2$ .
$P_2$ holds $R_2$ and waits for $R_3$ , which is held by $P_3$ .
$P_3$ holds $R_3$ and waits for $R_4$ , which is held by $P_4$ .
$P_4$ holds $R_4$ and waits for $R_1$ , which is held by $P_1$ .

In this situation, none of the processes can proceed, as each is waiting for a resource held by another process in the chain, resulting in a deadlock.

Preventing Circular Wait

To prevent Circular Wait and thus avoid deadlocks, various strategies can be applied:

Resource Hierarchy: Processes must request resources in a specific order. If all processes request resources in the same order, cyclic dependencies can be avoided.
Use of Timestamps: Processes can be assigned timestamps, and resources are only granted to processes with certain timestamps to ensure that no cyclic dependencies occur.
Design Avoidance: Ensure that the system is designed to exclude cyclic dependencies.

Preventing Circular Wait is a crucial aspect of deadlock avoidance, contributing to the stable and efficient operation of systems.

Created 4 Months ago