Trace the sequence of events when a user attempts to borrow a book that is currently checked out by another user in a concurrent environment. Which step correctly describes the system's behavior?
easy🧠🧾 Concept Trace Q12 of Q15
OOP & Design Patterns - Design a Library Management System - LLD with Relationships & Edge Cases
Trace the sequence of events when a user attempts to borrow a book that is currently checked out by another user in a concurrent environment. Which step correctly describes the system's behavior?
AThe Library class queues the request and processes it after the current loan expires without immediate feedback
BThe system immediately updates the book status to 'borrowed' for the requesting user without checking current loans
CThe User class updates its borrowed books list first, then the system verifies availability asynchronously
DThe LoanManager checks the book's availability, detects it is loaned out, and denies the request atomically
Step-by-Step Solution
Step 1: Check availability atomically
LoanManager must verify the book is available before granting loan to prevent race conditions.
Step 2: Why not immediate update?
The system immediately updates the book status to 'borrowed' for the requesting user without checking current loans risks data inconsistency by ignoring current loan state.
Step 3: Why not User updates first?
The User class updates its borrowed books list first, then the system verifies availability asynchronously breaks transactional integrity and can cause stale or conflicting states.
Step 4: Why not queue without feedback?
The Library class queues the request and processes it after the current loan expires without immediate feedback delays user feedback and complicates user experience; immediate denial is standard.
Final Answer:
Option D -> Option D
Quick Check:
Atomic availability check and denial maintain consistency and user clarity.
Quick Trick:Always verify resource availability atomically before state changes in concurrency [OK]
Common Mistakes:
MISTAKES
Assuming immediate state update without checks
Updating user state before system validation
Delaying feedback by queuing without immediate response
Trap Explanation:
PITFALL
Options A and C seem efficient but ignore concurrency risks; D seems user-friendly but impractical for immediate loan attempts.
Interviewer Note:
CONTEXT
Tests understanding of concurrency control and transactional integrity in LLD.
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