Question

Discuss the problems of deadlock and starvation, and the different approaches to dealing with these problems.

Short answer

Deadlock refers to a situation where processes are stuck because they are all waiting for each other to release resources, while starvation is a situation where a process is perpetually denied the necessary resources. Strategies to handle them include deadlock avoidance, deadlock detection-recovery, and ignoring for deadlock, while for starvation, solutions include 'Aging' and eliminating resource 'capture'.

Step-by-step solution

Understanding Deadlock

A deadlock can be comprehended as a situation in an operating system where two or more processes (jobs) are unable to proceed because each is waiting for the other to release a resource. Deadlocks can occur when multiple processes share a specific type of mutually exclusive resource known as a lock or when they involve multiple processes interacting at the same time (suitable conditions: Mutual Exclusion, Hold and Wait, No Preemption, and Circular Wait).

Understanding Starvation

Starvation occurs when one or many processes in a system are indefinitely not granted access to resources, causing them to wait indefinitely. This may occur in a system with priority-based scheduling, where a process with a low priority may never get scheduled, or a situation where a blocking process is given preference.

Approaches to Dealing with Deadlock and Starvation

Many strategies are available to handle deadlocks and starvation. For deadlocks, we can utilize (1) deadlock avoidance by not allowing the system to get into a deadlock state. (2) Deadlock detection-recovery, where we allow deadlocks, detect them and recover. (3) Ignoring the problem altogether, considering deadlocks happen infrequently. For starvation, common solutions are (1) Aging where priority of waiting process is gradually increased until it can access resources. (2) Eliminating the 'capture' of resources, where partial methods to resource requests are implemented, releasing a resource as soon as the process no longer needs it instead of holding it indefinitely.

Key concepts

Deadlock Avoidance

Deadlock avoidance is an operating system concept that aims to prevent deadlocks before they happen. It is achieved by careful resource allocation strategies, ensuring that a system will never enter an unsafe state where deadlocks are possible.

One common method of deadlock avoidance is the Banker's Algorithm, which simulates resource allocation and only proceeds if it determines that all processes can finish their tasks. In other words, the algorithm 'forecasts' resource requests and assesses if continuing with allocation would lead to a deadlock. If a potential deadlock is detected, the resource is not allocated to the requesting process.

By strictly managing and mapping out resource distribution in this preventative manner, the system ensures that it never reaches a point where a process must wait indefinitely for a resource held by another.

Deadlock Detection-Recovery

In contrast to avoidance, deadlock detection-recovery involves allowing a system to enter a deadlock and then employing methods to detect and correct the issue.

For detection, the system periodically checks for cycles in the resource allocation graph, which signify the presence of a deadlock. Once a deadlock is identified, recovery measures are necessary. Recovery can be a complex and sensitive process, sometimes involving resource preemption, process termination, or rolling back processes to a safe state.

Resource Preemption: This involves forcibly taking a resource away from a process. Process Termination: One or more processes involved in the deadlock may need to be ended. Roll Back: Processes are rolled back to an earlier state where they were not deadlocked. These methods can have significant performance implications and are thus used prudently.

Process Scheduling

Process scheduling is essential for multiprogramming in operating systems to ensure that each process gets an adequate amount of CPU time. This concept is also crucial in preventing starvation, where a process is perpetually waiting for its turn.

A scheduler determines the execution order of processes based on policies, such as first-come, first-served (FCFS), shortest job first (SJF), or priority scheduling, where processes with higher priorities are served first.

• FCFS: It is straightforward but can lead to long wait times.
• SJF: This can be efficient but difficult to predict the required time.
• Priority Scheduling: Affects resource allocation and can lead to starvation of low-priority processes.

High-level scheduling policies often implement measures such as priority aging to avoid starvation, thereby ensuring a more equitable distribution of CPU time among processes.

Resource Allocation

Resource allocation in operating systems is how system resources like CPU time, memory, and I/O are distributed among competing processes. Effective resource allocation is necessary to achieve a high level of system performance and responsiveness.

Allocation strategies may vary depending on the resource type and system architecture. For instance, memory can be allocated with strategies such as paging or segmentation, and I/O resources might be controlled via spooling or device reservation. The key is to prevent a situation where resources are held indefinitely, thus avoiding both deadlocks and starvation scenarios.

Resource allocation must be done carefully to ensure that all processes progress without undue delay. Ideally, an operating system allocates resources in a way that maximizes overall utility while being fair to individual processes. This can be a balanced act, requiring dynamic adjustment as the system load changes.