Parallel Computing Questions Medium
Deadlock in parallel computing refers to a situation where two or more processes are unable to proceed because each is waiting for the other to release a resource or complete a task. It is a state of impasse where the processes are stuck and cannot make any progress.
Deadlock occurs due to the presence of four necessary conditions, known as the Coffman conditions, which are:
1. Mutual Exclusion: At least one resource must be held in a non-sharable mode, meaning only one process can use it at a time.
2. Hold and Wait: A process holding at least one resource is waiting to acquire additional resources held by other processes.
3. No Preemption: Resources cannot be forcibly taken away from a process; they can only be released voluntarily.
4. Circular Wait: A circular chain of two or more processes exists, where each process is waiting for a resource held by the next process in the chain.
When these conditions are met, a deadlock can occur. Once a deadlock happens, the processes involved cannot proceed, leading to a halt in the execution of the parallel program.
To prevent or resolve deadlocks, various techniques can be employed. Some of the commonly used methods include:
1. Deadlock Prevention: This approach focuses on eliminating one or more of the Coffman conditions to prevent deadlocks from occurring. For example, by ensuring that processes request all their required resources at once or by using resource allocation strategies that avoid circular wait.
2. Deadlock Avoidance: This technique involves using algorithms and heuristics to dynamically analyze the resource allocation requests and determine if granting them would potentially lead to a deadlock. If a deadlock is predicted, the request is delayed or denied to avoid the deadlock situation.
3. Deadlock Detection and Recovery: This method involves periodically checking the system's resource allocation state to detect the presence of a deadlock. If a deadlock is detected, recovery mechanisms such as process termination or resource preemption can be employed to resolve the deadlock and allow the processes to proceed.
4. Deadlock Ignorance: In some cases, deadlocks are considered rare events, and the cost of implementing prevention, avoidance, or detection mechanisms outweighs the potential benefits. In such situations, the system may choose to ignore deadlocks and rely on manual intervention or system restarts if a deadlock occurs.
Overall, understanding and managing deadlocks is crucial in parallel computing to ensure efficient and reliable execution of parallel programs.