are produced and consumed summary of the messages that each actor understands and its associated response fig1 is a flowchart showing u201c unpin u201d function steps used to unpin a handle u201c unpin u201d function 1000 subroutine is initiated by start step 1002 in step 1004 an unpin handle message is sent then step 1006 is termination of the subroutine fig1 is a flowchart showing u201c identify u201d function steps used to identify a referenced handle u201c identify u201d function 1100 subroutine is initiated by start step 1102 in step 1104 the message counter is incremented by 1 note only one thread may access the collector 39 s message counter at a time in step 1106 a u201c blacken handle u201d message is sent then step 1108 is termination of the subroutine fig1 is a flowchart showing the process u201c pin u201d message and response steps used to pin a handle as identified in table iii u201c process pin message u201d function 1200 subroutine is initiated by start step 1202 the handle 39 s reference counter is incremented by 1 in step 1204 in step 1206 a query is made as to whether or not the reference count equals to 1 if the result of step 1206 is yes it will proceed to step 1210 wherein the handle is colored black subsequently in step 1212 the handle is moved into the pinned set then step 1208 is termination of the subroutine if the result of step 1206 is no it will proceed directly to step 1208 to terminate the subroutine fig1 is a flowchart showing the process u201c unpin u201d message and response steps used to unpin a handle as identified in table iii u201c process unpin message u201d function 1300 subroutine is initiated by start.