Question

Could anyone answer on these questions?

1) There is a Microsoft’s class: SafeHandle.cs I looked into the source and there are such methods:

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
[MethodImplAttribute(MethodImplOptions.InternalCall)]
public extern void DangerousAddRef(ref bool success);

or

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
[MethodImplAttribute(MethodImplOptions.InternalCall)]
public extern void DangerousRelease();

Where are the definitions of these method? Where Can I find them?

2) There is a method definitions which execute a method from the system library.

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail), SuppressUnmanagedCodeSecurity, DllImport("kernel32.dll", EntryPoint="WaitForSingleObject", SetLastError=true, ExactSpelling=true)]
private static extern int WaitForSingleObjectDontCallThis(SafeWaitHandle handle, int timeout);

Normally method: WaitForSingleObject accepts (HANDLE and DWORD).
How .net know how to obtain handle from the SafeWaitHandle class and how he does it?

Answer 1

1. This method implemented as unmanaged function internally. You can download Shared Source Common Language and take a look at that method implementation.

Here the code that I found in safechandle.cpp file:

FCIMPL2(void, SafeHandle::DangerousAddRef, SafeHandle* refThisUNSAFE, CLR_BOOL *pfSuccess)
{
    CONTRACTL
    {
        THROWS;
        MODE_COOPERATIVE;
        DISABLED(GC_TRIGGERS);
        SO_TOLERANT;
    }
    CONTRACTL_END;

    SAFEHANDLEREF sh(refThisUNSAFE);

    HELPER_METHOD_FRAME_BEGIN_1(sh);

    if (pfSuccess == NULL)
        COMPlusThrow(kNullReferenceException);

    sh->AddRef();
    *pfSuccess = TRUE;

    HELPER_METHOD_FRAME_END();
}
FCIMPLEND

But I’m not sure is it usefull or not.

---

And now about second question.

During marshalling from managed code to native code object marshallel converts any SafeHandle to IntPtr by calling DangerousGetHandle method.

During unmarshalling from native code to managed code there is opposed conversion: any IntPtr returns as SafeHandle.

When you’re calling any unmanaged code that takes DWORD or PVOID we could pass SafeHandle or one of its descendants.

For example if we have a couple of external functions in our umanaged DLL:

PVOID CreateCustomHandle();
void ReleaseCustomHandle(PVOID handle);

We could call them in following way:

[DllImport("kernel32")]
public static extern MySafeHandle CreateCustomHandle();

[DLLImport("kernel32")]
public static extern void ReleaseCustomHandle(MySafeHandle handle);

Where MySafeHandle is subclass of SafeHandle class that knows how to deal with that particular resource.