void Tcl_CreateCloseHandler(channel, proc, clientData)
void Tcl_DeleteCloseHandler(channel, proc, clientData)
Tcl_CreateCloseHandler arranges for proc to be called when channel is closed with Tcl_Close or Tcl_UnregisterChannel, or using the Tcl close command. Proc should match the following prototype:
typedef void Tcl_CloseProc( ClientData clientData);
The clientData is the same as the value provided in the call to Tcl_CreateCloseHandler.
Tcl_DeleteCloseHandler removes a close callback for channel. The proc and clientData identify which close callback to remove; Tcl_DeleteCloseHandler does nothing if its proc and clientData arguments do not match the proc and clientData for a close handler for channel.