Purpose
To provide, through a standard web-service interface, a simplified tuple-space-like capability which can be used by other services and by applications running in the ELF container.
We have chosen to implement this service instead of using JavaSpaces, the tuple-space which has long been part of the Jini Technology package (see http://java.sun.com/developer/products/jini and also http://javaspaces.org), for the following reasons:
- There are serious problems with using multicast technologies on NCSA's production resource subnets.
- We do not require the full peer-to-peer capabilities offered by Jini.
- We do not require the full generality of JavaSpaces with respect to serializable classes; our service accepts an open-ended (i.e., basically untyped) wrapper object containing as its payload element a serialized XML blob (which usually, but not necessarily, will implement
ncsa.tools.common.UserFacing
).
API
Service WSDL
ITupleSpace
Code Block |
---|
public interface ITupleSpace { Integer write( String entryXML ) throws Throwable; Integer[] writeB( String[] entryXML ) throws Throwable; String[] read( String matchXML, int max ) throws Throwable; String[] take( String matchXML, int max, long timeout ) throws Throwable; String[] takeNB( String matchXML, int max ) throws Throwable; } |
NOTES
write
takes a serialized string representing thencsa.service.vizier.tspace.TspaceEntry
object (see below); returns the entry id.writeB
is a batch method which does the same thing aswrite
on multiple entries; returns array of ids corresponding to each entry.read
andtake
are batch methods, both requiring a serialized string representing thencsa.service.vizier.tspace.TspaceMatchRequest
object (see below), along with an integer indicating the maximum number of entries to return (default is 10; it is advisable not to set this number too high, as Axis will have trouble managing extremely large SOAP packets); the array returned contains serializedncsa.service.vizier.tspace.TspaceEntry
objects.take
also requires a timeout (if set to t <= 0, the non-blocking method is called), whereastakeNB
will return immediately subsequent to issuing the request against the data store.takeNB
can returnnull
if no entries satisfy the request constraints.take
will not returnnull
unless timeout <= 0.take
may return an empty array (length 0) if its timeout has been exceeded.
ncsa.service.vizier.tspace.TspaceEntry
The object stored in the service's data store and which can be retrieved through the read
or take
ports. A fuller description of the object is found on the ncsa.tools.ogrscript.tspace page.
NOTE
When passing this object to the write
port, it is important that the id
attribute/field be handled correctly.
- If
id
isnull
, the object will be added as a new entry. - If
id
is notnull
, an attempt will be made to update an existing object with that id. The fields subject to update are:- timeTaken
- timeCompleted
- retried
- ranOn
If the id
is set, it is not necessary to provide a complete description of the entry; only the XML elements or attributes corresponding to the 4 updateable fields above will be processed. See further the ncsa.tools.ogrscript.tspace page.
ncsa.service.vizier.tspace.TspaceMatchRequest
The object used to express the match query parameter required by the read
or take
ports. A fuller description of the object is found on the ncsa.tools.ogrscript.tspace page.