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Questions and Answers
What is a necessary condition for a deadlock to occur?
What is a necessary condition for a deadlock to occur?
- Circular wait (correct)
- Deadlock detection
- Resource allocation graph
- Mutual exclusion (correct)
Which condition cannot be disallowed to prevent deadlock?
Which condition cannot be disallowed to prevent deadlock?
- Hold and wait
- No-preemption
- Mutual exclusion (correct)
- Circular wait
How can the hold and wait condition be prevented?
How can the hold and wait condition be prevented?
- By enabling processes to release resources freely
- By allowing processes to hold resources indefinitely
- By allowing processes to execute in any order
- By requiring processes to request all resources at once (correct)
An indirect method of deadlock prevention involves disallowing which conditions?
An indirect method of deadlock prevention involves disallowing which conditions?
During deadlock detection, what is the approach taken with resource requests?
During deadlock detection, what is the approach taken with resource requests?
What does a resource allocation graph represent in the context of deadlocks?
What does a resource allocation graph represent in the context of deadlocks?
What strategy is suggested for deadlock avoidance?
What strategy is suggested for deadlock avoidance?
Which of the following is a common characteristic of deadlock?
Which of the following is a common characteristic of deadlock?
What is the primary function of a binary semaphore?
What is the primary function of a binary semaphore?
Which scenario illustrates a deadlock condition?
Which scenario illustrates a deadlock condition?
Which statement best describes mutual exclusion?
Which statement best describes mutual exclusion?
In the context of concurrency, which of these is true about consumable resources?
In the context of concurrency, which of these is true about consumable resources?
Which operation can lead to the blocking of a process in a semaphore?
Which operation can lead to the blocking of a process in a semaphore?
What is a common method for preventing deadlock in resource allocation?
What is a common method for preventing deadlock in resource allocation?
Which of the following statements about resource allocation graphs is true?
Which of the following statements about resource allocation graphs is true?
What differentiates a mutual exclusion lock from a binary semaphore?
What differentiates a mutual exclusion lock from a binary semaphore?
Which condition ensures that at least one resource is held in a non-sharable mode to potentially lead to deadlock?
Which condition ensures that at least one resource is held in a non-sharable mode to potentially lead to deadlock?
In a resource allocation graph, what does an edge directed from a process to a resource indicate?
In a resource allocation graph, what does an edge directed from a process to a resource indicate?
What condition describes a situation where a thread holds at least one resource while waiting for additional resources?
What condition describes a situation where a thread holds at least one resource while waiting for additional resources?
Which of the following accurately describes the circular wait condition?
Which of the following accurately describes the circular wait condition?
Which deadlock condition states that resources cannot be forcibly removed from a process?
Which deadlock condition states that resources cannot be forcibly removed from a process?
What type of resource allocation can help prevent deadlocks by limiting resource requests?
What type of resource allocation can help prevent deadlocks by limiting resource requests?
Which of the following would NOT be considered a mechanism to avoid deadlock?
Which of the following would NOT be considered a mechanism to avoid deadlock?
Which of the following statements accurately reflects mutual exclusion in the context of deadlock?
Which of the following statements accurately reflects mutual exclusion in the context of deadlock?
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Study Notes
Deadlock Conditions
- Four conditions are essential for a deadlock to occur.
- First three conditions are necessary, but not sufficient.
- Fourth condition is crucial for a deadlock to happen. This condition is a result of the first three.
- Deadlock can be portrayed as a circular wait that cannot be resolved.
Deadlock Prevention
- Deadlock prevention aims to eliminate at least one of the four deadlock conditions.
- Prevents deadlocks by incorporating safety measures into system design.
Indirect Deadlock Prevention
- Mutual Exclusion: This condition is generally unavoidable when resource access requires shared execution.
- Hold and Wait: This condition can be prevented by forcing a process to request all required resources simultaneously. The process is blocked until all resources can be allocated at once.
Deadlock Detection
- Allows resource requests when possible, but periodically checks for deadlocks and takes corrective actions.
- Does not restrict resource access or process execution.
- The operating system periodically runs algorithms to detect circular wait conditions.
Deadlock Characteristics
- Resource Allocation Graph: A directed graph depicting the resource allocation state, representing processes and resources as nodes, connected by edges.
- An edge from a process to a resource indicates a request not yet granted.
- A dot within the resource node shows a granted request.
- An edge from a resource node dot to a process signifies a received resource.
General Resource Categories
- Reusable Resources: Used by one process at a time and do not get consumed. For example, disk files and tape drives.
- Consumable Resources: Resources created and consumed, for example, messages.
Concurrency Mechanisms
- Counting Semaphore: Integer value used for signaling processes. Operations include initialization, decrement, and increment.
- Binary Semaphore: A semaphore with values 0 and 1, similar to a mutex lock.
- Mutex Lock: Similar to a binary semaphore, ensuring mutual exclusion.
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