[Java-player-users] ClassCastException: javaclient2. requestInterface ...

[Shawn L. <sla...@at...>]

Hello All,

    I'm new to the list, so please forgive me if this has been 
addressed. It is quite similar to the issue Radu encoutered in this 
thread: 
"http://sourceforge.net/mailarchive/forum.php?thread_id=9923107&forum_id=44859". 
  Hugo presented a dirty hack to fix it, but it seems, well, dirty.

    The problem we've encountered here pertains to requesting 
interfaces.    At the end of this note I included a copy of 
requestGripperInterface for  reference. My first question is, what 
version of Java this is compiled against and why are generics not used, 
or a general requestInterface where you pass in the interface you want? 
  Since all these functions are identical save for 
"PLAYER_<interface>_CODE" or such they could easily be combined into one 
method.

    The second question is more of a bug and also is of more 
consequence.   Similar to the referenced post concerning reading, the 
two methods requestDeviceAccess and isReadyRequestDevice come 
immediately after each other.  However, there is no guarantee that stage 
has returned the device yet, especially in a resource limited platform. 
This call then returns null.  Let's assume, for a minute, that the 
programmer decides to assume things have succeeded and a request is then 
made for a different device.  It executes the requestDeviceAccess method 
but before isReadyRequestDevice is called, stage returns the first 
interface while the 2nd is now delayed.  isReadyRequestDevice now 
returns true but the wrong interface is stored in newpd.  With how this 
is coded, the 2nd requestInterface will attempt to cast newpd as the 2nd 
interface. This will throw the ClassCastException as newpd contains the 
first interface.

    Possible solutions:
1) Typecheck!
2) Wait/Sleep for 100ms before checking isReadyRequestDevice
3) Poll newpd, saving them as they come in. On future requests for the 
device with same parameters use the already returned devices listing.

   What are your thoughts on this?  Is this better handled by the 
developer's alias instead of this user's alias?  Thank you for your 
assistance!

~ Shawn M Lavelle
   ATCorp R&D


public GripperInterface requestInterfaceGripper (int index, int access) {
     	requestDeviceAccess (PLAYER_GRIPPER_CODE, index, access);
     	if (isReadyRequestDevice ())
     		return (GripperInterface)newpd;
     	else
     		return null;
     }