VixDiskLib_Attach Error

I use VixDiskLib_Attach to attach a snapshot to a base vmdk. Then it told error ：  Disk "/root/abc.vmdk" is open using transport mode "file".
FILE: FileIO_Lock on '/root/abc.vmdk' failed: Lock timed out
FILE: FileIO_Lock on '/root/abc.vmdk' failed: Lock timed out
FILE: FileIO_Lock on '/root/abc.vmdk' failed: Lock timed out
FILE: FileIO_Lock on '/root/abc.vmdk' failed: Lock timed out
FILE: FileIO_Lock on '/root/abc.vmdk' failed: Lock timed out
FILE: FileIO_Lock on '/root/abc.vmdk' failed: Lock timed out
Error: [vixDiskLibSample.cpp:643]  3e8c The parent of this virtual disk could not be opened

My Code is :

   VixError vixError;

   VixDisk parentDisk(appGlobals.connection, appGlobals.parentPath, 0);

   VixDisk childrenDisk(appGlobals.connection, appGlobals.diskPath, 0);

   vixError = VixDiskLib_Attach(parentDisk.Handle(), childrenDisk.Handle()); 

   CHECK_AND_THROW(vixError);

Any help would be appreciated.

Is there any sample for VixDiskLib_Attach？