Deadlock

Definition

Deadlock is a situation in computing where two or more processes are unable to proceed because each is waiting for the other to release resources. This situation typically arises in inter-task communication and synchronization, as processes may hold certain resources while simultaneously requesting others, leading to a standstill where no process can move forward. Understanding deadlock is crucial for designing systems that can efficiently manage resource allocation and ensure process execution without interruption.

5 Must Know Facts For Your Next Test

1. Deadlock occurs when there is a circular wait condition where each process is waiting for a resource held by another process in the cycle.
2. Four necessary conditions must hold true for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait.
3. Deadlocks can lead to severe performance degradation in systems, as affected processes remain in a state of perpetual waiting.
4. There are several strategies for handling deadlock, including prevention, avoidance, detection, and recovery methods.
5. Deadlock detection algorithms can be implemented to periodically check system states and identify deadlocks so they can be resolved.

Review Questions

• What are the four necessary conditions for deadlock to occur, and how do they interrelate?
  • The four necessary conditions for deadlock are mutual exclusion, hold and wait, no preemption, and circular wait. Mutual exclusion ensures that only one process can use a resource at a time. Hold and wait means that a process holding some resources can request additional ones. No preemption implies that resources cannot be forcibly taken from processes holding them. Circular wait occurs when a group of processes are each waiting on resources held by another in the group. When all four conditions exist simultaneously, deadlock can occur.
• Discuss some strategies that can be employed to handle deadlocks in embedded systems design.
  • Strategies for handling deadlocks include prevention, avoidance, detection, and recovery. Prevention involves designing the system to ensure that at least one of the four necessary conditions cannot hold. Avoidance requires dynamic decision-making to ensure that resource allocation does not lead to deadlock states. Detection periodically checks the system for deadlocks, allowing for intervention if detected. Recovery methods may involve terminating or rolling back processes to break the deadlock cycle. These strategies help maintain system reliability and performance.
• Evaluate the impact of deadlock on system performance and the effectiveness of various resolution techniques.
  • Deadlock can significantly degrade system performance by halting processes that are essential for operations. As processes remain blocked indefinitely, the overall efficiency of the system drops due to wasted CPU cycles and unutilized resources. Various resolution techniques have their pros and cons; prevention might reduce flexibility while detection could introduce overhead from constant monitoring. In evaluating these techniques, it's crucial to balance between system complexity and performance requirements to ensure efficient resource management without compromising process execution.

Related terms

Mutex: A mutex, short for mutual exclusion, is a synchronization primitive used to prevent multiple processes from accessing shared resources simultaneously.

Semaphore: A semaphore is a signaling mechanism that controls access by multiple processes to shared resources, used to prevent race conditions and manage resource allocation.

Starvation: Starvation occurs when a process is perpetually denied the resources it needs to proceed, often because other processes are constantly prioritized over it.