What is a deadlock?
💡 Concept: Deadlock
A deadlock is a situation in multithreaded applications where two or more threads are blocked forever, waiting for each other’s resources.
📘 Quick Intro
Deadlocks cause programs to hang or become unresponsive, making it critical to understand and prevent them.
🧠 Analogy
Imagine two people each holding a key the other needs and neither is willing to release it — they’re stuck waiting indefinitely.
🔧 Technical Explanation
- 🔒 Occurs when multiple threads hold locks and wait for others.
- ⏳ Circular wait condition is essential for deadlock.
- ⚠️ Leads to resource starvation and halted progress.
- 🛠️ Can be detected via thread dumps and debugging.
- 🔑 Avoided by careful lock ordering and timeout strategies.
🎯 Use Cases (Prevention)
- ✅ Acquire locks in a consistent order.
- ✅ Use timeout when waiting for locks.
- ✅ Minimize lock scope and avoid nested locks.
- ✅ Employ higher-level concurrency constructs where possible.
💻 Code Example
// Example of potential deadlock
object lockA = new object();
object lockB = new object();
void Thread1() {
lock(lockA) {
Thread.Sleep(100);
lock(lockB) {
Console.WriteLine(""Thread1 acquired both locks"");
}
}
}
void Thread2() {
lock(lockB) {
Thread.Sleep(100);
lock(lockA) {
Console.WriteLine(""Thread2 acquired both locks"");
}
}
}
❓ Interview Q&A
Q1: What is a deadlock?
A: A state where threads wait indefinitely for each other.
Q2: What causes deadlocks?
A: Circular lock dependencies.
Q3: How to prevent deadlocks?
A: Consistent lock order and timeouts.
Q4: Can deadlocks be detected?
A: Yes, through debugging tools.
Q5: What is circular wait?
A: Condition where threads wait in a cycle.
Q6: Does thread starvation differ from deadlock?
A: Yes, starvation is resource denial, deadlock is mutual waiting.
Q7: What tools help detect deadlocks?
A: Visual Studio debugger, WinDbg.
Q8: Is locking always bad?
A: No, it’s necessary but must be managed carefully.
Q9: What is lock ordering?
A: Acquiring locks in a predefined sequence.
Q10: Can async code cause deadlocks?
A: Yes, especially with improper synchronization.
📝 MCQs
Q1. What is a deadlock?
- Program crashes
- Threads wait indefinitely
- Threads run normally
- Error thrown
Q2. What causes deadlocks?
- No locks
- Circular lock dependencies
- Single thread
- No resource
Q3. How to prevent deadlocks?
- Random order
- Consistent lock order
- Ignore locks
- More threads
Q4. Can deadlocks be detected?
- No
- Yes
- Sometimes
- Never
Q5. What is circular wait?
- One thread waiting
- Threads waiting in a cycle
- No waiting
- Error
Q6. Does starvation differ from deadlock?
- No
- Yes
- Maybe
- Sometimes
Q7. Tools to detect deadlocks?
- Task Manager
- Visual Studio debugger
- Event Viewer
- Registry
Q8. Is locking always bad?
- Yes
- No
- Sometimes
- Never
Q9. What is lock ordering?
- Random sequence
- Predefined lock sequence
- No sequence
- Any sequence
Q10. Can async cause deadlocks?
- No
- Yes
- Sometimes
- No idea
💡 Bonus Insight
Understanding deadlocks and how to avoid them is crucial for reliable multithreaded C# applications.
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