What is a deadlock and how can you prevent it in .NET?

Question

Anubhav Kumar · Answer

A deadlock is a situation where two or more threads (or tasks) are
waiting for each other to release resources, and none of them ever proceed — resulting in a permanent blocking cycle.
In .NET, deadlocks can occur in:
Multithreading (e.g., lock)Asynchronous code (async/await)Database transactions
Threading Deadlock Example
object lockA = new object();
object lockB = new object();
void Thread1()
{
    lock (lockA)
    {
        Thread.Sleep(100); // Give Thread2 a chance to lock B
        lock (lockB)
        {
            // do something
        }
    }
}
void Thread2()
{
    lock (lockB)
    {
        Thread.Sleep(100);
        lock (lockA) // Deadlock: Thread1 holds A, waits for B; Thread2 holds B, waits for A
        {
            // do something
        }
    }
}
Deadlock in Async/Await
public string GetData()
{
    return GetDataAsync().Result; // blocks UI thread
}
public async Taskandlt;stringandgt; GetDataAsync()
{
    await Task.Delay(1000); // Tries to resume on captured (blocked) UI thread → deadlock
    return "done";
}
This causes a deadlock especially in UI apps like WinForms/WPF.
How to Prevent Deadlocks
1. Always Acquire Locks in the Same Order
Avoid circular waits.
lock (lockA)
{
    lock (lockB)
    {
        // Safe if always A → B
    }
}
2. Avoid Synchronous Blocking on Async Code
Prefer await over .Result or .Wait()
public async Taskandlt;stringandgt; GetDataAsync()
{
    await Task.Delay(1000);
    return "done";
}
// Good
string result = await GetDataAsync();
3. Use Timeout with Locks
bool lockTaken = Monitor.TryEnter(lockA, TimeSpan.FromSeconds(2));
if (lockTaken)
{
    try
    {
        // do work
    }
    finally
    {
        Monitor.Exit(lockA);
    }
}
else
{
    // handle lock timeout
}
4. Use ConfigureAwait(false) in Library Code
Prevents deadlocks by not capturing the synchronization context:
await Task.Delay(1000).ConfigureAwait(false);
5. Use SemaphoreSlim Instead of
lock for Async
private readonly SemaphoreSlim _semaphore = new(1, 1);
public async Task SafeMethodAsync()
{
    await _semaphore.WaitAsync();
    try
    {
        // thread-safe async logic
    }
    finally
    {
        _semaphore.Release();
    }
}
Summary
Aspect
Details
What is Deadlock?
Two or more threads/tasks waiting indefinitely for each other
Causes
Improper lock order, blocking async code, nested transactions
Prevention Tips
Lock ordering, avoid .Result, use timeouts, prefer await, use
ConfigureAwait(false)
and

forum

What is a deadlock and how can you prevent it in .NET?

ICSM Computer

Can you answer this question?

1 Answers

Threading Deadlock Example

Deadlock in Async/Await

How to Prevent Deadlocks

1. Always Acquire Locks in the Same Order

2. Avoid Synchronous Blocking on Async Code

3. Use Timeout with Locks

4. Use `ConfigureAwait(false)` in Library Code

5. Use `SemaphoreSlim` Instead of `lock` for Async

Summary

Liked By

Aspect	Details
What is Deadlock?	Two or more threads/tasks waiting indefinitely for each other
Causes	Improper lock order, blocking async code, nested transactions
Prevention Tips	Lock ordering, avoid `.Result`, use timeouts, prefer `await`, use `ConfigureAwait(false)`

forum

What is a deadlock and how can you prevent it in .NET?

ICSM Computer

Can you answer this question?

1 Answers

Threading Deadlock Example

Deadlock in Async/Await

How to Prevent Deadlocks

1. Always Acquire Locks in the Same Order

2. Avoid Synchronous Blocking on Async Code

3. Use Timeout with Locks

4. Use ConfigureAwait(false) in Library Code

5. Use SemaphoreSlim Instead of lock for Async

Summary

Liked By

4. Use `ConfigureAwait(false)` in Library Code

5. Use `SemaphoreSlim` Instead of `lock` for Async