Marshal.FreeHGlobal Failure

Hello,
I am fairly new to all this and I am hoping somone can help. I am writing a C# application that requires use of the Clipborad for inter-process communication. C# has methods I can leverage in order to accomplish this:

 

 Clipboard.SetText(string);

Unfortunately, there is an unacceptable delay when using this call. The receiving process does not recognize its presence for over 5 seconds. As such, moved onto native Win32 SDK calls. Namely: SetClipboardData() and its required support functions. This call gives me the speed I require as the contents are transferred near immediately to the clipboard when I use the native methods. Unfortunately, the call to free allocalted heap memory failes like clockwork on the fourth iteration.
When I comment out the FreeHGlobal function (bad juju...), everything operates as expected. Here is the class I use to use native methods:

 
class ClipboardHelper
{
[DllImport("user32.dll")]
static extern bool OpenClipboard(IntPtr hWndNewOwner);
[DllImport("user32.dll")]
static extern bool EmptyClipboard();
[DllImport("user32.dll")]
static extern IntPtr SetClipboardData(uint uFormat, IntPtr hMem);
[DllImport("user32.dll")]
static extern bool CloseClipboard();
[DllImport("kernel32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
public static extern IntPtr GlobalFree(IntPtr handle);

// Metafile mf is set to a state that is not valid inside this function.
static public bool PutTextOnClipboard(IntPtr hWnd, StringBuilder s)
{
   bool bResult = false;
   if (OpenClipboard(hWnd))
   {
      IntPtr ptr = Marshal.StringToHGlobalAnsi(s.ToString());

      if (EmptyClipboard())
      {
         IntPtr hRes = SetClipboardData(1, ptr);
         CloseClipboard();
      }
      Marshal.FreeHGlobal(ptr);
      //GlobalFree(ptr);
   }
   return true;

}

The top level exception is:

 
An unhandled exception of type 'System.StackOverflowException' occurred in mscorlib.dll

Does anyone have any idea what I am doing wrong here?
Partial stack trace:

 

 mscorlib.dll!System.AccessViolationException.AccessViolationException() + 0x14 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Reflection.CustomAttributeEncodedArgument.ParseAttributeArguments(System.Reflection.ConstArray attributeBlob, ref System.Reflection.CustomAttributeCtorParameter[] customAttributeCtorParameters, ref System.Reflection.CustomAttributeNamedParameter[] customAttributeNamedParameters, System.Reflection.RuntimeModule customAttributeModule) + 0x5b bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.CustomAttributeData(System.Reflection.RuntimeModule scope, System.Reflection.CustomAttributeRecord caRecord) + 0x4c4 bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.GetCustomAttributes(System.Reflection.RuntimeModule module = {System.Reflection.RuntimeModule}, int tkTarget) + 0x53 bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.GetCustomAttributesInternal(System.Reflection.RuntimeAssembly target = {System.Reflection.RuntimeAssembly}) + 0x47 bytes 
  mscorlib.dll!System.Reflection.RuntimeAssembly.GetCustomAttributesData() + 0x5 bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.GetCustomAttributes(System.Reflection.Assembly target) + 0x21 bytes 
  mscorlib.dll!System.Resources.ManifestBasedResourceGroveler.GetNeutralResourcesLanguage(System.Reflection.Assembly a = {System.Reflection.RuntimeAssembly}, ref System.Resources.UltimateResourceFallbackLocation fallbackLocation = MainAssembly) + 0x31 bytes 
  mscorlib.dll!System.Resources.ResourceManager.CommonSatelliteAssemblyInit() + 0x6d bytes 
  mscorlib.dll!System.Resources.ResourceManager.ResourceManager(string baseName, System.Reflection.Assembly assembly = {System.Reflection.RuntimeAssembly}) + 0x51 bytes 
  mscorlib.dll!System.Environment.ResourceHelper.GetResourceStringCode(object userDataIn) + 0x111 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Environment.ResourceHelper.GetResourceString(string key, System.Globalization.CultureInfo culture) + 0xd1 bytes 
  mscorlib.dll!System.Environment.GetResourceStringLocal(string key) + 0x48 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Runtime.InteropServices.COMException.COMException() + 0x14 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Runtime.InteropServices.Marshal.FreeHGlobal(System.IntPtr hglobal) + 0x74 bytes

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

theLizard16y ago
Can you explain what the receiving app does, an example of the message sent via clipboard and what the app does when it sees the clipboard message. is the app a windows based app with text boxes, combo boxes etc and do the messages affect these, if so how.

It is very difficult to formulate a solution without knowing a lot more details, It may be possible to use the send keys command to the specific window in the other process, it is not that difficult to do or it could be possible to use SendMessage( .... ) to the window process.
Ken Pendlebury16y ago
I am trying to communicate simple text-based commands to a seperate process that "listens" to the clipboard. Commands are decorated with special text to identify them as such. When the receiving app detects their presence, it removes them from the clipboard and processes the requested command.
Thanks.
theLizard16y ago
What are you trying to communicate? maybe there is another way, but need to know answer to this question.
Ken Pendlebury16y ago
Please note that Clipboard-based inter-process communication is not a choice I have made because I thought it was a great idea. I am using this methodology because the receiving process API is already defined and I have no control over it.