How to debug a deadlock?

c# multithreading deadlock
Matthew Scharley picture Matthew Scharley · Jul 18, 2009 · Viewed 17.5k times · Source

Other than that I don't know if I can reproduce it now that it's happened (I've been using this particular application for a week or two now without issue), assuming that I'm running my application in the VS debugger, how should I go about debugging a deadlock after it's happened? I thought I might be able to get at call stacks if I paused the program and hence see where the different threads were when it happened, but clicking pause just threw Visual Studio into a deadlock too till I killed my application.

Is there some way other than browsing through my source tree to find potential problems? Is there a way to get at the call stacks once the problem has occured to see where the problem is? Any other tools/tips/tricks that might help?

Answer

chris166 picture chris166 · Jul 18, 2009

What you did was the correct way. If Visual Studio also deadlocks, that happens now and then. It's just bad luck, unless there's some other issue.

You don't have to run the application in the debugger in order to debug it. Run the application normally, and if the deadlock happens, you can attach VS later. Ctrl+Alt+P, select the process, choose debugger type and click attach. Using a different set of debugger types might reduce the risk of VS crashing (especially if you don't debug native code)

A deadlock involves 2 or more threads. You probably know the first one (probably your UI thread) since you noticed the deadlock in your application. Now you only need to find the other one. With knowledge of the architecture, it should be easy to find (e.g. what other threads use the same locks, interact with the UI etc)

If VS doesn't work at all, you can always use windbg. Download here: http://www.microsoft.com/whdc/devtools/debugging/default.mspx

Related questions

Transaction (Process ID) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction

I have a C# application which is inserting data into SQL Server (2008) table using stored procedure. I am using multi-threading to do this. The stored procedure is being called from inside the thread. Now my stored procedure is using "tablock" …

Read More
Re-entrant locks in C#

Will the following code result in a deadlock using C# on .NET? class MyClass { private object lockObj = new object(); public void Foo() { lock(lockObj) { Bar(); } } public void Bar() { lock(lockObj) { // Do something } } }

Read More
Sample code to illustrate a deadlock by using lock(this)

I've read several articles and posts that say that lock(this), lock(typeof(MyType)), lock("a string") are all bad practice because another thread could lock on the same key and cause a deadlock. In order to understand this problem, …

Read More