c# - How do I obtain a crash dump

Question

I need to get a crash dump from a program. How do i get it? The Program is written in C#. What exactly is a crash dump? When is it created? Where is it saved? How do i read it?

Answer 1

Since you are saying C# I assume you are using the Windows platform.

A crashdump, or just dump, is the complete memory snapshot and other related system info of a process at a particular point in time. Dumps can be used to debug program crashes, hangs, memory and resource leaks and probably more problems I have not listed here.

In the case of crashes and hangs the first piece of data you want to obtain from a crash dump will be the callstack. This indicates the point of a crash or the point at which an operation blocked and never returned so the program sits and does nothing.

For resource leaks multiple memory dumps of a process can be collected over a period of time and examined to see which objects in memory are growing the most. This can help narrow down which parts of the code are causing the leak. To learn more about debugging specific issues I highly recommend this blog.

There are a few ways to capture a dump file.

1. Procdump (http://technet.microsoft.com/en-us/sysinternals/dd996900.aspx)
2. Visual Studio 2010 (http://msdn.microsoft.com/en-us/library/vstudio/fk551230(v=vs.100).aspx)
3. WinDbg - Not to bad but more intimidating than other tools

With procdump you can simply do:

c:>procdump.exe -ma YourProcessName.exe

The result of this command will be a full memory snapshot of YourProcessName.dmp written to c: . The -ma switch specifies dumping a complete memory image. If you are debugging a crash or hang you can likely get away without the -ma switch. Keep in mind without the full memory dump when you go to examine data structures you probably won't have valid data. Without the full memory dump you will still have callstack data which is often good enough for crashes and hangs. I typically error on the side of harddrive space is cheap so collect the full dump.

Procdump will also automatically take dumps at time intervals or when a specific condition is met. Read the documentation at the link above for more info. One switch I would recommend is -e.

c:>procdump.exe -ma -e YourProcessName.exe

Instead of writing the dump immediately it will only write it when your program crashes.

With Visual Studio 2010 you can attach to the process with the debugger and save a dump file. (Keep in mind when you F5 debug your program Visual Studio automatically attaches). When your program is in a "break state" (breakpoint, unhandled exception, crash) the Debug menu will have the option to Save Dump As.... Then you can save that dump any where you would like.

Since you mentioned C# you are very likely collecting managed dump files. The easiest way is to use Visual Studio 2010. Simply, open up the dump file you created as you would any other file and begin debugging.

However, if that is not an option you can always use VS2008 or WinDbg with the SOS extensions. I do highly recommend Visual Studio 2010 though as SOS extensions and WinDbg in general have a pretty steep learning curve. To learn more about SOS check out these MSDN articles here and here.

Another reason I recommend using Visual Studio or procdump is that they will collect the dump file you expect. I recommend steering clear of Task Manager's "Create Dump File Tool". The reason being it will collect 64bit dumps of 32bit processes which are overly difficult to debug.