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Deadlock Detection in Distributed Systems

Last Updated on June 7, 2024 by Abhishek Sharma

Distributed systems consist of multiple autonomous computers that communicate through a network and coordinate their actions to achieve a common goal. As these systems grow in complexity, the risk of deadlocks increases. A deadlock occurs when a set of processes are blocked because each process is waiting for a resource held by another process in the set, creating a cycle of dependencies that cannot be resolved. Detecting and handling deadlocks in distributed systems is crucial for maintaining system reliability and performance. This article explores the intricacies of deadlock detection in distributed systems, various detection algorithms, and strategies for handling deadlocks.

What is Deadlock in Operating System?

Deadlocks are a critical issue in operating systems (OS) that can severely impact system performance and reliability. A deadlock occurs when a set of processes become permanently blocked because each process is waiting for a resource that is held by another process in the set. This results in a situation where none of the processes can proceed, effectively halting the system’s progress. Understanding, detecting, and resolving deadlocks is essential for maintaining the efficiency and stability of an operating system.

Conditions for Deadlock

A deadlock situation arises when the following four conditions hold simultaneously in a system:

  • Mutual Exclusion: At least one resource must be held in a non-sharable mode, meaning only one process can use the resource at a time.
  • Hold and Wait: A process holding at least one resource is waiting to acquire additional resources currently held by other processes.
  • No Preemption: Resources cannot be forcibly taken from processes; they must be released voluntarily.
  • Circular Wait: A set of processes are waiting for each other in a circular chain, where each process holds at least one resource needed by the next process in the chain.

Deadlock in Distributed Systems

In distributed systems, detecting deadlocks is more challenging due to the lack of a global view of the system state. Each process has only partial knowledge of the resources and their allocation, making it difficult to identify cycles in resource dependencies. Moreover, network delays and failures can complicate the detection process.

Deadlock Detection Strategies

Deadlock detection in distributed systems can be categorized into three main strategies:

  • Centralized Deadlock Detection
  • Distributed Deadlock Detection
  • Hierarchical Deadlock Detection

Centralized Deadlock Detection

In centralized deadlock detection, a single coordinator is responsible for detecting deadlocks. The coordinator maintains a global wait-for graph (WFG), representing resource dependencies among processes.


  • Collect Information: Each process periodically sends its local resource allocation and wait-for information to the coordinator.
  • Update Global WFG: The coordinator updates the global WFG using the information received from all processes.
  • Detect Cycles: The coordinator runs a cycle detection algorithm on the global WFG. If a cycle is detected, a deadlock exists.
  • Resolve Deadlock: The coordinator initiates actions to break the deadlock, such as aborting one or more processes in the cycle.

Advantages and Disadvantages

  • Advantages: Simplifies the deadlock detection process by centralizing it, making it easier to implement and manage.
  • Disadvantages: The coordinator can become a bottleneck and a single point of failure. It may also struggle with scalability as the number of processes increases.

Distributed Deadlock Detection

In distributed deadlock detection, there is no single coordinator. Instead, each process participates in detecting deadlocks, collaborating with other processes to build a global view of resource dependencies.

1. Path-Pushing Algorithm
Concept: Processes exchange information about their dependencies by propagating paths of resource requests.


  • Each process sends its current wait-for path to its neighbors.
  • Upon receiving a path, a process extends it with its own dependencies and forwards it.
  • If a process detects a cycle in the path, a deadlock is declared.

2. Edge-Chasing Algorithm
Concept: Processes send probes along resource request edges to detect cycles.


  • A process holding a resource sends a probe to the process waiting for it.
  • Each receiving process forwards the probe to the next process in the wait-for chain.
  • If a probe returns to the originating process, a cycle (and thus a deadlock) is detected.

3. Global State Detection
Concept: Periodically capture a consistent global state of the system and analyze it for cycles.


  • Use a distributed snapshot algorithm to collect the global state.
  • Construct the global WFG from the snapshot.
  • Run a cycle detection algorithm on the global WFG to identify deadlocks.

Advantages and Disadvantages

  • Advantages: Avoids the single point of failure and bottleneck issues of centralized detection. More scalable and resilient to failures.
  • Disadvantages: More complex to implement and manage. Communication overhead can be significant, especially in large systems.

Hierarchical Deadlock Detection

Hierarchical deadlock detection combines elements of both centralized and distributed approaches. The system is divided into clusters, each with a local coordinator responsible for detecting deadlocks within the cluster. A global coordinator oversees the local coordinators and detects deadlocks spanning multiple clusters.


  • Local Detection: Local coordinators detect deadlocks within their clusters using centralized or distributed algorithms.
  • Global Coordination: Local coordinators report potential deadlocks to the global coordinator.
  • Global Detection: The global coordinator constructs a higher-level WFG from the reports and runs a cycle detection algorithm to identify inter-cluster deadlocks.

Advantages and Disadvantages

  • Advantages: Balances the load between local and global coordinators, improving scalability and fault tolerance.
  • Disadvantages: Adds complexity due to multiple layers of coordination. Local deadlocks might still affect overall system performance.

Handling Deadlocks

Once a deadlock is detected, the system must take action to resolve it. Common strategies for handling deadlocks include:

  • Abort Processes: Terminate one or more processes involved in the deadlock cycle to break the cycle and release resources.
  • Resource Preemption: Forcefully take resources away from some processes and reassign them to others. This approach requires careful management to avoid further deadlocks.
  • Process Rollback: Roll back one or more processes to a previous safe state, freeing resources and allowing processes to continue.

Criteria for Selecting Processes to Abort

When choosing processes to abort, the system can consider several criteria:

  • Priority: Abort the process with the lowest priority.
  • Execution Time: Abort the process that has executed the least, minimizing wasted computation.
  • Resource Usage: Abort the process holding the fewest resources to reduce the impact on the system.
  • Process Age: Abort the youngest process, assuming it has less progress and state to lose.

Deadlock detection in distributed systems is a complex but essential task for ensuring system reliability and performance. Centralized, distributed, and hierarchical detection strategies each offer unique advantages and challenges. Effective deadlock detection requires careful consideration of system architecture, communication overhead, and fault tolerance. By understanding and implementing appropriate deadlock detection and handling mechanisms, distributed systems can achieve high levels of efficiency and robustness, even in the face of growing complexity and scale.

FAQs related to Deadlock Detection in Distributed Systems

Below are some of the FAQs related to Deadlock Detection in Distributed Systems:

Q1: What is a Resource Allocation Graph (RAG)?
A Resource Allocation Graph (RAG) is a directed graph used to represent the state of resource allocation in a system. Vertices represent processes and resources, and edges represent the allocation and request of resources. A cycle in the RAG indicates a potential deadlock.

Q2: How can deadlocks be prevented?
Deadlock prevention involves ensuring that at least one of the necessary conditions for deadlock cannot hold. Strategies include:

  • Ensuring resources are sharable (preventing mutual exclusion).
  • Requiring processes to request all needed resources at once or releasing all held resources before requesting new ones (preventing hold and wait).
  • Allowing preemption of resources (preventing no preemption).
  • Imposing a total ordering of resource types and requiring processes to request resources in increasing order (preventing circular wait).

Q3: What is the Banker’s Algorithm?
The Banker’s Algorithm is a deadlock avoidance algorithm that simulates resource allocation to ensure the system remains in a safe state. It checks whether granting a resource request would leave the system in a state where all processes can eventually obtain their maximum resource needs and complete execution.

Q4: How can deadlocks be detected?
Deadlocks can be detected using algorithms that periodically check the system for cycles in the resource allocation graph (RAG). For systems with single instances of each resource type, cycle detection is used. For systems with multiple instances of each resource type, a more complex algorithm is needed to construct and analyze a wait-for graph (WFG).

Q5: What actions can be taken to resolve a detected deadlock?
To resolve a detected deadlock, the system can:

  • Abort Processes: Terminate one or more processes involved in the deadlock.
  • Resource Preemption: Forcefully take resources away from some processes and reassign them to others, possibly rolling back processes to safe states.

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