windows - How to avoid a Win32 exception when accessing Process.MainModule.FileName in C#?

Question

I started a new project listing the full paths to all running processes. When accessing some of the processes the program crashes and throws a Win32Exception. The description says an error occured while listing the process modules. Initially I thought this problem might occur because I'm running it on a 64-bit platform, so I recompiled it for the CPU types x86 and AnyCPU. I'm getting the same error, though.

Process p = Process.GetProcessById(2011);
string s = proc_by_id.MainModule.FileName;

The error occurs in line #2. The blank fields show processes where the error occured:

Is there any way to get around this error message?

question from:https://stackoverflow.com/questions/9501771/how-to-avoid-a-win32-exception-when-accessing-process-mainmodule-filename-in-c

Answer 1

The exception is thrown when you try to access the MainModule property. The documentation for this property does not list Win32Exception as a possible exception, but looking at the IL for the property it is evident that accessing it may throw this exception. In general it will throw this exception if you are trying to do something that is impossible or not allowed in the OS.

Win32Exception has the property NativeErrorCode and also a Message that will explain what the problem is. You should use that information to troubleshoot your problem. NativeErrorCode is the Win32 error code. We can guess all day long what the problem is but the only way to actually figure this out is to inspect the error code.

But to continue guessing, one source of these exceptions is accessing 64 bit processes from a 32 bit process. Doing that will throw a Win32Exception with the following message:

A 32 bit processes cannot access modules of a 64 bit process.

You can get the number of bits of your process by evaluating Environment.Is64BitProcess.

Even running as a 64 bit process you will never be allowed to access MainModule of process 4 (System) or process 0 (System Idle Process). This will throw a Win32Exception with the message:

Unable to enumerate the process modules.

If you problem is that you want to make a process listing similar to the one in Task Manager you will have to handle process 0 and 4 in a special way and give them specific names (just as Task Manager does). Note that on older versions of Windows the system process has ID 8.