What is Deadlock in Operating Systems

Here we know what is oprating system and why is happened on operating systems (OS), and it may have an impact on system stability and performance.

While deadlock can certainly have negative impacts for system performance, that there are various techniques and algorithms available to prevent and resolve deadlock situations in operating system. There are many strategies have , such as resource allocation policies and deadlock detection mechanisms, can mitigate the risks associated with deadlock situations and improve system reliability.

Why do deadlock situations happened ?

Deadlock happens when two or more processes are unable to go forward because one is waiting for the other to take action or release a resource. This circumstance results in a halt, in which none of the processes involved can proceed. Understanding the causes of deadlock, as well as preventive measures and deadlock resolution procedures, is critical for keeping computer systems running smoothly and reliably.

refrences credit https://www.geeksforgeeks.org/what-is-an-operating-system/

How do we know Deadlock occurred?

A deadlock is a situation in a computer system in which a set of processes are interrupted because one is holding a resource while another is waiting for another resource. In simplest way we can say , it’s like a traffic jam in which one car waits for the other to move and no one can go. This might be particularly problematic in our systems that need high performance and reliability, including web servers, databases, and real-time applications.

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Deadlock conditions.

Deadlock occurs when four specific situations, sometimes known as the Coffman conditions, are satisfied simultaneously: there are some imporant point must we know to prevent and resolve deadlock conditions.

1. Mutual Exclusion: At least one resource must be saved in a non-shareable format. That is, only one process may use the resource at any time. For example, a printer cannot be used by two different processes at once.

2. Hold and Wait: A process with at least one resource waits for additional resources from other processes. For example, one process may handle a printer while another holds the file.

3. No Preemption: Resources cannot be withdrawn from a process by force; instead, they must be willingly abandoned by the process that holds them. This means that the operating system cannot take resources from a process in order to settle a deadlock.

4. Circular Wait: A chain of processes waits for one another. Each process includes at least one resource needed by the next process in the chain. For example, process A waits for a resource held by process B, which in turn waits for a resource held by process C, and so on, until the last process waits for a resource held by process A.

These scenarios are prevalent in environments where many applications are running concurrently and need exclusive access to resources. Identifying and addressing these criteria is crucial for preventing and resolving impasses.

Deadlock Characterization

Understanding the nature and behavior of deadlock in an operating system is part of the deadlock characterization. This includes determining how mutual exclusion, hold and wait, no preemption, and circular wait contribute to deadlock situations.

Mutual exclusion is a fundamental aspect of many deadlock situations. Certain resources, such as printers, disk drives, or files, cannot be shared by many processes at once. For example, a printer can only print one document at a time. If one operation uses the printer, the others must wait till it is available. This unique access provides an opportunity for stalemate provided other prerequisites are met.

Hold and Wait in Deadlock

The hold and wait condition occurs when processes that retain resources seek more resources held by other processes. This circumstance No Preemption in Deadlock

No preemption implies that resources cannot be removed forcefully from processes that contain them. Processes must release resources willingly. This circumstance complicates deadlock resolution since the operating system cannot recover resources from processes in order to Circular Wait in Deadlock

Circular delay is perhaps the most visible characteristic of standstill. It consists of a sequence of processes in which each process waits for a resource held by the next process in the chain, resulting in a closed loop. For example, in a system with three processes (A, B, and C) and three resources, a cyclic wait occurs when A waits for a resource owned by B, B waits for a resource held by C, and C waits for a resource held by A, resulting in stalemate.

 Deadlock Prevention and Handling

Deadlocks must be avoided and resolved in order for systems to function properly and reliably. Various strategies may be used to prevent deadlocks and to handle them when they occur.

Deadlock Prevention

Deadlock prevention entails designing the system such that one or more of the required circumstances for deadlock cannot be met. There are many ways that may be utilized to accomplish this:

1. Eliminating Mutual Exclusion: This method entails designing resources to be shared wherever feasible. For example, spooling for printers enables many processes to contribute print jobs to a queue without requiring exclusive access.

2. Avoiding keep and Wait: Processes must request all resources at once and cannot keep them while waiting for others. This strategy may result in poor resource consumption, but it helps to avoid stalemate.

3. Allowing Preemption: To prevent stalemate, the system might preempt resources from one process and assign them to another. This method may be difficult to apply since it may require reverting processes to a safe state.

4. Circular Wait Prevention: One way to avoid circular wait is to apply tight resource acquisition sequencing. Processes must request resources in a prescribed sequence to avoid creating a circular chain of dependencies.

#### Deadlock Avoidance

Deadlock avoidance involves the use of algorithms to dynamically assess the resource allocation status in order to ensure that no deadlock occurs. The Banker’s method is a common tool for this purpose, since it assesses whether a resource allocation request can be safely granted without ending in stalemate. If the system detects that granting the request may result in a deadlock, it denies it and causes the process to wait.

### Deadlock Detection and Recovery

Even with preventive and avoidance measures in place, deadlocks may still occur. In these cases, the operating system must detect and recover from deadlocks. Deadlock detection entails regularly monitoring the system’s resource allocation state to identify halted processes. Once noticed, the system may employ a variety of recovery strategies:

1. Resource Preemption: Temporarily removing resources from processes to resolve deadlocks. This strategy may require reverting processes to a prior safe state and reallocating resources.

2. Process Termination: Terminating one or more processes that are causing the impasse in order to free up resources and resolve it. This method may be extreme, resulting in lost effort, yet it can be useful in breaking impasse cycles.

3. Rollback and Restart: Reverting processes to a safe state and resuming them to prevent deadlocks. This strategy requires the maintenance of process state checkpoints, which might be resource heavy.

 Real-World Examples of Deadlock

Consider the following basic example of deadlock: two processes, A and B, and two resources, X and Y. Assume that process A possesses resource X and demands resource Y, but process B owns resource Y and requests resource X. Both processes are now waiting for resources owned by the other, resulting in a stalemate. Neither process can progress, therefore the system is basically stuck.

Another example is a database system in which several transactions need access to different tables. If transaction T1 locks Table A while waiting for Table B, and transaction T2 locks Table B while waiting for Table A, a deadlock results. Both transactions are waiting for resources owned by the other, thus the database system must interfere to break the impasse.

Conclusion:

Deadlock is a complex and challenging problem in operating systems that may have a significant impact on system performance and reliability. System administrators and developers must grasp the causes, characteristics, and remedies to deadlock. Operating systems can maintain stability and ongoing operation in the face of resource conflicts by implementing effective preventative, avoidance, and detection procedures. As computer systems become more complex and networked, deadlock resolution remains an essential aspect of operating system design and maintenance.