What is deadlock? – An easy-to-understand explanation of the basic concepts and countermeasures of parallel processing systems

Explanation of IT Terms

What is Deadlock?


Deadlock is a common problem in parallel processing systems that can bring the system to a halt. It occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. In other words, it’s a situation where a group of processes is stuck in a circular wait, unable to make progress.

Understanding Deadlock

To understand deadlock, let’s consider a simple scenario. Imagine two processes, A and B, both needing two resources to complete their tasks. Process A acquires resource 1 and then waits for resource 2, which is currently held by Process B. Similarly, Process B acquires resource 2 and waits for resource 1, held by Process A. This creates a deadlock state, where neither process can proceed unless one of them releases its resource.

Types of Deadlocks

There are several types of deadlocks that can occur in parallel processing systems. Let’s briefly discuss two common types:

1. Resource Deadlock: This occurs when a process requires additional resources to complete its execution and waits indefinitely for them to become available. The resources may be held by other processes, causing a deadlock situation.

2. Storage Deadlock: In this type of deadlock, different processes access storage resources such as disk drives or memory. If they hold exclusive locks on particular resources and need access to additional resources that are currently held by other processes, a deadlock can occur.

Preventing and Managing Deadlocks

Preventing deadlocks is crucial to maintaining the efficiency of parallel processing systems. Here are some common strategies to prevent and manage deadlocks:

1. Resource Allocation: Implement proper resource allocation techniques, such as deadlock detection algorithms, to identify potential deadlock situations. This helps in resolving deadlocks proactively before they occur.

2. Resource Ordering: Establish a strict order on how processes request and obtain resources. This can help prevent circular waits and potential deadlocks.

3. Deadlock Detection and Recovery: Implement deadlock detection algorithms that periodically check for deadlocks in the system. If a deadlock is detected, the system can take appropriate actions to recover from the deadlock, such as killing a process or releasing resources.

4. Resource Preemption: Allow resource preemption, which means forcibly removing resources from one process and reallocating them to another. This can prevent permanent deadlocks but should be used cautiously to avoid system instability.

5. Avoidance Techniques: Use resource scheduling algorithms that determine whether the requested resources will lead to a deadlock. If a potential deadlock is detected, the system can reject the request or modify the allocation to avoid the deadlock situation.


Understanding deadlock and implementing effective countermeasures is essential in parallel processing systems. By properly managing resources, preemptively identifying potential deadlock situations, and applying preventive techniques, we can maintain the stability and efficiency of these systems. Deadlocks are a challenging problem, but with the right strategies, they can be effectively minimized.

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