Introduction of Deadlock in Operating System

Deadlock in an operating system refers to a situation where a set of processes are unable to proceed because each process in the set is waiting for a resource that another process in the set holds, causing a cycle of dependency. In simpler terms, deadlock occurs when processes get stuck in a state where they are all waiting for resources that are locked by other processes in the same set, and none can proceed. This leads to the processes being unable to complete their tasks, causing system resources to be wasted.

What is a Deadlock?

Deadlock is a state in which two or more processes are unable to proceed because each is waiting for a resource that the other holds, resulting in a cycle of dependencies. The processes involved in the deadlock situation are said to be deadlocked because they cannot continue execution without intervention from the operating system.

Conditions for Deadlock

For deadlock to occur, four necessary conditions must hold simultaneously. These conditions are often referred to as the Coffman conditions, named after the researchers who defined them:

• Mutual Exclusion:At least one resource must be held in a non-shareable mode, meaning only one process can use it at a time. Example: A printer can only be used by one process at a time.

• Hold and Wait: A process holding at least one resource is waiting to acquire additional resources that are currently being held by other processes. Example: Process A holds a printer and waits for a scanner, while Process B holds a scanner and waits for the printer.

• No Preemption: Resources cannot be forcibly taken away from processes holding them. A process must release the resource voluntarily when it is no longer needed. Example: If Process A is holding a printer and is waiting for a scanner, the system cannot force Process A to give up the printer.

• Circular Wait: A set of processes exist such that each process in the set is waiting for a resource that another process in the set holds, forming a cycle of dependencies. Example: Process A waits for Process Bs resource, Process B waits for Process Cs resource, and Process C waits for Process As resource, forming a circular chain.

Effects of Deadlock

• System Inefficiency: Deadlock leads to the wastage of resources that are held by processes that cannot make progress.

• Process Starvation: Some processes may never get the resources they need if they are involved in a deadlock.

• System Unresponsiveness: The system may appear frozen or unresponsive because processes cannot complete their tasks due to deadlock.

How to prevent Deadlock

• Prevention: The operating system can prevent deadlock by ensuring that at least one of the Coffman conditions is not met. For example, preventing circular wait can be done by requiring processes to request all the resources they will need at once (no hold and wait).

• Avoidance: Deadlock avoidance algorithms, such as the Banker's Algorithm, dynamically analyze resource requests to ensure the system never enters a state where deadlock could occur.

• Detection and Recovery: Some systems allow deadlock to occur but periodically check for it. If deadlock is detected, the system takes action to recover, such as terminating a process or forcibly preempting resources.