我应该从P / Invoke不安全代码中得到什么例外？

Question

In my solution I've written the following:

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern unsafe bool CopyFileEx(string lpExistingFileName,  
 string lpNewFileName, CopyProgressRoutine lpProgressRoutine, IntPtr lpData,  
 Boolean* pbCancel,    CopyFileFlags dwCopyFlags);

...

bool result;

unsafe{
  result = CopyFileEx(sourceFile, targetFile, null, IntPtr.Zero,  
                      null /* pointer */, 0);
}

if(!result)
    Win32Exception exc = new Win32Exception(Marshal.GetLastWin32Error()); 
// parameter could be omitted according to Win32Exception constructor 
// implementation

In the assumption that CopyFileEx was exported with SetLastError = true parameter of DllImport attribute, do I have a chance to get any unhalted exception here?

I'm specifically interested in non-CLR exceptions which are wrapped in RuntimeWrappedException instance. In C++ "throw 1" is a valid construct. So what exceptions should I expect from such P/Invoke calls and where I can obtain such information regarding exceptions (MSDN says nothing regarding exceptions from CopyFileEx)?

Answer 1

If a DLL uses the Win32 structured exception handling system, then any exceptions thrown by the DLL will be translated to OutOfMemoryException , AccessViolationException , NullReferenceException (rarely), or SEHException .

RuntimeWrappedException is only used when managed C++ throws a non- Exception -derived object. It is not used for unmanaged DLLs. If you had a managed C++ DLL that did a throw 1 , then you could catch RuntimeWrappedException .

SEHException acts as a catch-all for the unmappable types of SEH exceptions from unmanaged DLLs. This would include any C++ class, or the throw 1 example. AFAIK, there is no way to pull the C++-specific exception info out of SEHException , though I'm sure it's hackable if you try hard enough.

Note that there are a few DLLs that do not use the Win32 structured exception handling system. Most notably Cygwin DLLs. In that case, any C++ exception is likely to crash the process or at least your thread. Naturally, all the Windows DLLs (including the one defining CopyFileEx ) do use Win32 structured exception handling, as do any unmanaged DLLs created by Microsoft's C++ compiler.

Also note that the Win32 API (including CopyFileEx ) does not normally report errors using Win32 structured exceptions; they report them via GetLastError . The only way to get most Win32 functions to throw a Win32 structured exception is to pass it wildly invalid arguments (such as asking it to write into the middle of ntdll.dll ).