Why booking tests availability and concurrency in LLD - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to ensure the booking system checks availability before confirming.

LLD

if slot.is_available() and not slot.[1]():
    slot.book()

Drag options to blanks, or click blank then click option'

Ais_locked

Bis_full

Cis_reserved

Dis_open

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_full instead of is_locked causes race conditions.

The slot must not be locked by another process to allow booking, so is_locked is the correct check.

2fill in blank

medium

Complete the code to lock the slot before booking to handle concurrency.

LLD

def book_slot(slot):
    if slot.[1]():
        slot.lock()
        slot.book()

Drag options to blanks, or click blank then click option'

Ais_locked

Bis_booked

Cis_reserved

Dis_available

Attempts:

3 left

💡 Hint

Common Mistakes

Locking without checking availability leads to errors.

We must check if the slot is available before locking it to prevent double booking.

3fill in blank

hard

Fix the error in the concurrency control to prevent double booking.

LLD

def book_slot(slot):
    if slot.is_available():
        slot.[1]()
        slot.book()

Drag options to blanks, or click blank then click option'

Areserve

Bunlock

Clock

Dcancel

Attempts:

3 left

💡 Hint

Common Mistakes

Unlocking before booking causes race conditions.

Locking the slot before booking prevents other processes from booking the same slot concurrently.

4fill in blank

hard

Fill both blanks to implement optimistic concurrency control in booking.

LLD

def book_slot(slot, version):
    if slot.version == [1]:
        slot.book()
        slot.version = [2]

Drag options to blanks, or click blank then click option'

Aversion

Bversion + 1

Cversion - 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Decrementing version causes incorrect concurrency control.

Check the current version matches, then increment version after booking to detect conflicts.

5fill in blank

hard

Fill all three blanks to implement a thread-safe booking with locking and availability check.

LLD

def safe_book(slot):
    with slot.[1]():
        if slot.[2]():
            slot.[3]()

Drag options to blanks, or click blank then click option'

Alock

Bis_available

Cbook

Dunlock

Attempts:

3 left

💡 Hint

Common Mistakes

Checking availability outside lock causes race conditions.

Use a lock context to ensure thread safety, check availability, then book the slot.