:Deadlocks In Operating System:
What is Process In Operating System ?
In the context of operating systems, a process is a program in execution. It is an independent entity that carries out tasks within a system. Processes are fundamental to the operation of modern computer systems, and understanding their states and life cycle is crucial for effective system management. Let’s delve into the concepts of processes, states, and life cycle:
1. What is Process In Operating System ?
Definition: A process is an instance of a computer program that is being executed. It is a dynamic entity that undergoes various changes during its lifetime.
Attributes of Process :
– Program Counter (PC): Indicates the address of the next instruction to be executed.
– Registers: Temporary storage for data and instructions.
– Memory: The space allocated for the process.
– Open Files: References to files and resources.
– Process ID (PID): A unique identifier for each process.
2.States of a Process In Operating System :
A process undergoes different states during its execution. The states are typically defined as follows:
– New: The process is being created.
– Ready: The process is ready to execute and waiting for the CPU.
– Running: The process is actively executing on the CPU.
– Blocked (Waiting): The process is waiting for an event (e.g., I/O completion) to proceed.
– Terminated: The process has finished its execution.
3.Life Cycle of a Process In Operating System :
The life cycle of a process includes its creation, execution, and termination. It is often represented as a state transition diagram.
– Creation: The process is created either by the operating system or through a parent process.
– Ready: The process moves to the ready state, indicating it is prepared for execution.
– Running: The process is given access to the CPU and enters the running state.
– Blocked: If the process needs to wait for an event (e.g., I/O operation), it enters the blocked state.
– Completion: When the process finishes its execution, it moves to the terminated state.
4. Transitions Between States Of Process In Operating System :
– Admission: Transition from the new state to the ready state.
– Dispatch: Transition from the ready state to the running state.
– Interrupt: Transition from the running state to the ready state.
– Event Wait: Transition from the running state to the blocked state.
– Event Occurrence: Transition from the blocked state to the ready state.
– Exit: Transition from any state to the terminated state.
5. Process Control Block (PCB):
Each process is associated with a Process Control Block, which contains information about the process’s state, program counter, registers, and other essential details.
Understanding the life cycle and states of a process is essential for efficient resource management in an operating system. Processes allow for multitasking and concurrent execution, enabling a computer system to handle multiple tasks simultaneously. The transitions between states are managed by the operating system’s scheduler, which determines which process to run next based on scheduling algorithms and priorities.
What is Deadlock In Operating System ?
A deadlock in operating systems occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. Essentially, a set of processes becomes deadlocked when each process is holding a resource and waiting for another resource acquired by some other process in the set.
To better understand a deadlock, it’s crucial to recognize the conditions that must be present:
1. Mutual Exclusion: At least one resource must be held in a non-shareable mode, meaning only one process can use it at a time.
2. Hold and Wait: A process is currently holding resources while also waiting for additional resources that are currently held by other processes.
3. No Preemption: Resources cannot be forcibly taken away from a process. They must be explicitly released by the process holding them.
4. Circular Wait: There must exist a circular chain of two or more processes, each waiting for a resource held by the next one in the chain.
When these conditions are met, a deadlock can occur, leading to a situation where none of the processes can proceed, and the system essentially comes to a standstill.
Example of Deadlock In Operating System :
Consider two processes, Process 1 and Process 2, and two resources, Resource 1 and Resource 2. If Process 1 holds Resource 1 and is waiting for Resource 2, while Process 2 holds Resource 2 and is waiting for Resource 1, a circular wait is formed, fulfilling the conditions for a deadlock.
Effects of Deadlocks In Operating System :
1. Resource Wastage: Resources are held by processes that cannot proceed, leading to potential resource wastage.
2. Reduced Throughput: The overall throughput of the system is reduced as processes are unable to complete their execution.
3. Increased Waiting Times: Processes stuck in a deadlock have increased waiting times, affecting system responsiveness.
Handling Deadlocks:
1. Prevention: Ensure that at least one of the necessary conditions for a deadlock (mutual exclusion, hold and wait, no preemption, circular wait) is never satisfied.
2. Avoidance: Use algorithms to dynamically analyze resource allocation requests to ensure that deadlocks will not occur.
3. Detection and Recovery: Periodically check for the presence of deadlocks and take corrective actions, such as process termination or resource preemption.
4. Ignorance: Some systems choose to ignore the deadlock problem, assuming that deadlocks will be rare or that the cost of prevention/avoidance is higher than dealing with occasional deadlocks.
Deadlocks are a significant challenge in operating system design, and managing them effectively is crucial for ensuring the reliability and efficiency of computer systems.
Prevention Of Deadlock in Operating System ?
Deadlock prevention involves designing the system in a way that at least one of the necessary conditions for a deadlock (mutual exclusion, hold and wait, no preemption, circular wait) is never satisfied. Here are some strategies to prevent deadlocks:
1. Mutual Exclusion:
Prevent Mutual Exclusion: Ensure that resources, whenever possible, are shareable, meaning multiple processes can access them simultaneously without interference.
2. Hold and Wait:
Immediate Allocation: Processes must request and be allocated all required resources at once before execution. This prevents a process from holding some resources and waiting for others.
3. No Preemption:
Resource Preemption: Allow the operating system to preempt resources from a process when necessary. If a process requests a resource that is already allocated to another process, the OS can preempt the resource from the currently holding process and allocate it to the requesting process.
4. Circular Wait:
Assign Resource Order: Impose a total order on all resources and require that each process requests resources in an increasing order. This prevents circular waiting.
5. Use of Resource Allocation Graphs:
Graph-Based Methods: Represent resource allocation and request relationships using a resource allocation graph. Apply techniques such as Banker’s Algorithm to ensure that resource allocation doesn’t lead to deadlock.
6. Resource Allocation Policies:
Conservative Resource Allocation: The system only grants a resource request if it is certain that it can satisfy the request without leading to deadlock.
7. Timeouts and Rollbacks:
Timeouts: Introduce timeouts for resource requests. If a process doesn’t obtain all required resources within a specified time, it releases any acquired resources and restarts the process.
Rollback: Allow a process to roll back to a previously consistent state when deadlock is detected.
8. State Prevention:
Avoidance of Unsafe States: Prevent the system from reaching unsafe states where deadlock can occur. Employ methods like the Banker’s algorithm to check whether resource allocation will lead to a safe state.
9. Dynamic Resource Allocation:
Dynamic Allocation and Deallocation: Allow processes to dynamically allocate and deallocate resources, preventing situations where a process holds resources unnecessarily.
10. Communication Instead of Competition:
Message Passing: Instead of competing for resources, processes communicate and share information through message passing, reducing the need for mutual exclusion.
It’s important to note that deadlock prevention strategies often come with trade-offs, and the chosen method depends on the specific requirements and characteristics of the system. Additionally, some prevention techniques may increase system complexity or impact overall system performance, so careful consideration is necessary during the design phase.