Race condition problem in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the shared resource in a race condition scenario.

Operating Systems

shared_variable = [1]

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

Athread

Bcounter

Clock

Dprocess

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'thread' or 'process' which are entities, not resources.

The shared resource in a race condition is typically a variable like counter that multiple threads access simultaneously.

2fill in blank

medium

Complete the sentence to explain what causes a race condition.

Operating Systems

A race condition occurs when multiple threads [1] a shared resource without proper synchronization.

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

Aaccess

Block

Ccreate

Dterminate

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'lock' which is a solution, not the cause.

Race conditions happen when multiple threads access the same resource at the same time without controls.

3fill in blank

hard

Fix the error in the statement about race conditions.

Operating Systems

Race conditions happen when threads [1] a resource sequentially without synchronization.

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

Aaccess concurrently

Block

Cterminate

Daccess

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'access' which implies any access, not necessarily concurrent.

Race conditions occur when threads access concurrently a resource without synchronization, not sequentially.

4fill in blank

hard

Fill both blanks to complete the code snippet that prevents race conditions using locks.

Operating Systems

lock = [1]()
lock.[2]()
# critical section code
lock.release()

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

ALock

Bacquire

Cstart

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' or 'run' which are unrelated to locking.

To prevent race conditions, a Lock object is created and its acquire method is called before entering the critical section.

5fill in blank

hard

Fill all three blanks to complete the explanation of race condition consequences.

Operating Systems

If threads [1] a shared resource [2] synchronization, it can lead to [3] results.

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

Aaccess

Bwithout

Cunexpected

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'create' which does not fit the context.

When threads access a shared resource without synchronization, it can cause unexpected or incorrect results.

Practice

1. What is a race condition in operating systems?

easy

A. When multiple processes access shared data simultaneously without proper control

B. When a process runs slower than expected

C. When a program crashes due to memory overflow

D. When a system runs out of disk space

Solution

1. Step 1: Understand the definition of race condition

   A race condition occurs when two or more processes access shared data at the same time without synchronization.

2. Step 2: Identify the correct description

   When multiple processes access shared data simultaneously without proper control correctly describes this situation, while others describe unrelated problems.

3. Final Answer:

   When multiple processes access shared data simultaneously without proper control -> Option A

4. Quick Check:

   Race condition = simultaneous uncontrolled access [OK]

Hint: Look for simultaneous access without control [OK]

Common Mistakes:

• Confusing race condition with system crashes
• Thinking it relates to disk space issues
• Mixing it up with slow process execution

2. Which of the following is a common method to prevent race conditions?

easy

A. Running processes sequentially without any synchronization

B. Using locks or mutexes to control access

C. Deleting shared data

D. Increasing CPU speed

Solution

1. Step 1: Identify synchronization methods

   Locks and mutexes are tools used to control access to shared data and prevent race conditions.

2. Step 2: Evaluate other options

   Increasing CPU speed or deleting data does not prevent race conditions. Running processes sequentially without synchronization is unsafe.

3. Final Answer:

   Using locks or mutexes to control access -> Option B

4. Quick Check:

   Locks prevent race conditions [OK]

Hint: Choose synchronization tools like locks [OK]

Common Mistakes:

• Thinking faster CPU fixes race conditions
• Ignoring the need for synchronization
• Assuming deleting data helps

3. Consider two processes incrementing a shared counter without locks. What is the likely outcome?

medium

A. The system will throw a syntax error

B. The counter will always increase correctly by 2

C. The counter will reset to zero automatically

D. The counter might increase incorrectly due to overlapping updates

Solution

1. Step 1: Understand concurrent increments without locks

   Without locks, both processes may read the same value before incrementing, causing lost updates.

2. Step 2: Identify the effect on the counter

   This leads to the counter increasing incorrectly, not by the expected total increments.

3. Final Answer:

   The counter might increase incorrectly due to overlapping updates -> Option D

4. Quick Check:

   Race condition causes incorrect increments [OK]

Hint: Look for overlapping updates causing errors [OK]

Common Mistakes:

• Assuming increments always add correctly
• Expecting syntax errors from concurrency
• Thinking counter resets automatically

4. Given this code snippet, what is the main problem causing a race condition?

shared_counter = 0

process1() {
  temp = shared_counter
  temp = temp + 1
  shared_counter = temp
}

process2() {
  temp = shared_counter
  temp = temp + 1
  shared_counter = temp
}

medium

A. The increment operation is atomic and safe

B. The variable shared_counter is not declared

C. Both processes read and write shared_counter without synchronization

D. The processes run sequentially

Solution

1. Step 1: Analyze access to shared_counter

   Both processes read, modify, and write shared_counter without any locks or synchronization.

2. Step 2: Identify the race condition cause

   This unsynchronized access can cause lost updates because the operations are not atomic.

3. Final Answer:

   Both processes read and write shared_counter without synchronization -> Option C

4. Quick Check:

   Unsynchronized access causes race condition [OK]

Hint: Check if shared data access is synchronized [OK]

Common Mistakes:

• Assuming increment is atomic
• Ignoring synchronization needs
• Thinking variables must be declared explicitly

5. Two threads update a shared bank account balance without locks. Thread A reads balance $100, adds $50, Thread B reads balance $100, subtracts $30. What is the possible incorrect final balance due to race condition?

hard

A. $150

B. $120

C. $130

D. $180

Solution

1. Step 1: Understand the operations without synchronization

   Thread A reads 100, plans to write 150; Thread B reads 100, plans to write 70.

2. Step 2: Identify race condition effect

   If Thread A writes 150, then Thread B overwrites with 70, or vice versa, one update is lost. If both read 100 before writing, possible final balances are 150 or 70, both incorrect (expected sequential: 120).

3. Step 3: Calculate possible incorrect final balance

   For example, if Thread B writes 70 first, then Thread A writes 150, final balance is $150 (lost B's update).

4. Final Answer:

   $150 -> Option A

5. Quick Check:

   Race condition causes incorrect balance $150 [OK]

Hint: Check if updates overwrite each other without locks [OK]

Common Mistakes:

• Assuming both updates always apply correctly
• Ignoring lost update problem
• Confusing addition and subtraction effects