Electrical computers and digital processing systems: multicomput – Computer network managing – Network resource allocating
Reexamination Certificate
1998-08-27
2003-01-07
Burgess, Glenton B. (Department: 2153)
Electrical computers and digital processing systems: multicomput
Computer network managing
Network resource allocating
Reexamination Certificate
active
06505250
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of client/server (also known as “distributed”) computing, where one computing device (“the client”) requests another computing device (“the server”) to perform part of the client's work.
BACKGROUND OF THE INVENTION
Client/server computing has become more and more important over the past few years in the information technology world. This type of distributed computing allows one machine to delegate some of its work to another machine that might be, for example, better suited to perform that work.
The benefits of client/server computing have been even further enhanced by the use of a well-known computer programming technology called object-oriented programming (OOP), which allows the client and server to be located on different (heterogeneous) “platforms”. A platform is a combination of the specific hardware/software/operating system/communication protocol which a machine uses to do its work. OOP allows the client application program and server application program to operate on their own platforms without worrying how the client application's work requests will be communicated and accepted by the server application. Likewise, the server application does not have to worry about how the OOP system will receive, translate and send the server application's processing results back to the requesting client application.
Details of how OOP techniques have been integrated with heterogeneous client/server systems are explained in U.S. Pat. No. 5,440,744 and European Patent Published Application No. EP 0 677,943 A2. These latter two publications are hereby incorporated by reference. However, an example, of the basic architecture will be given below for contextual understanding of the invention's environment.
As shown in
FIG. 1
, the client computer
10
(which could, for example, be a personal computer having the IBM OS/2 operating system installed thereon) has an application program
40
running on its operating system (“IBM” and “OS/2” are trademarks of the International Business Machines corporation). The application program
40
will periodically require work to be performed on the server computer
20
and/or data to be returned from the server
20
for subsequent use by the application program
40
. The server computer
20
can be, for example, a high-powered mainframe computer running on IBM's MVS operating system (“MVS” is also a trademark of the IBM corp.). For the purposes of the present invention it is irrelevant whether the requests for communications services to be carried out by the server are instigated by user interaction with the first application program
40
, or whether the application program
40
operates independently of user interaction and makes the requests automatically during the running of the program.
When the client computer
10
wishes to make a request for the server computer
20
's services, the first application program
40
informs the first logic means
50
of the service required. It may for example do this by sending the first logic means the name of a remote procedure along with a list of input and output parameters. The first logic means
50
then handles the task of establishing the necessary communications with the second computer
20
with reference to definitions of the available communications services stored in the storage device
60
. All the possible services are defined as a cohesive framework of object classes
70
, these classes being derived from a single object class. Defining the services in this way gives rise to a great number of advantages in terms of performance and reusability.
To establish the necessary communication with the server
20
, the first logic means
50
determines which object class in the framework needs to be used, and then creates an instance of that object, a message being sent to that object so as to cause that object to invoke one of its methods. This gives rise to the establishment of the connection with the server computer
20
via the connection means
80
, and the subsequent sending of a request to the second logic means
90
.
The second logic means
90
then passes the request on to the second application program
100
(hereafter called the service application) running on the server computer
20
so that the service application
100
can perform the specific task required by that request, such as running a data retrieval procedure. Once this task has been completed the service application may need to send results back to the first computer
10
. The server application
100
interacts with the second logic means
90
during the performance of the requested tasks and when results are to be sent back to the first computer
10
. The second logic means
90
establishes instances of objects, and invokes appropriate methods of those objects, as and when required by the server application
100
, the object instances being created from the cohesive framework of object classes stored in the storage device
110
.
Using the above technique, the client application program
40
is not exposed to the communications architecture. Further the service application
100
is invoked through the standard mechanism for its environment; it does not know that it is being invoked remotely.
The Object Management Group (OMG) is an international consortium of organizations involved in various aspects of client/server computing on heterogeneous platforms as is shown in FIG.
1
. The OMG has set forth published standards by which client computers (e.g. 10) communicate (in OOP form) with server machines (e.g. 20). As part of these standards, an Object Request Broker has been defined, which provides the object-oriented bridge between the client and the server machines. The ORB decouples the client and server applications from the object oriented implementation details, performing at least part of the work of the first and second logic means
50
and
90
as well as the connection means
80
.
FIG. 2
shows a conventional architecture for such a system. Once client requests find their way through the ORB
21
and into the server, the ORB finds a particular server object capable of executing the request and sends the request to that server object's object adapter
22
(also defined by OMG standard) where it is stored in the object adapter's buffer to await processing by the server object. The buffer is a First-In-First-Out queue, meaning that the first request received in the buffer at one end thereof is the first to leave out the other end. The server object has a plurality of parallel execution threads (
23
a
,
23
b
,
23
c
) upon any of which it can run an instance of itself. In this way, the server object is able to process plural requests at the same time. The object adapter
22
looks to see which of the parallel execution threads is ready to process another request and assigns the request located at the end of the buffer to the next available execution thread. This is explained in the above-mentioned U.S. Patent as a “dispatching” mechanism whereby the server dispatches queued requests to execution threads.
One major problem with this prior architecture is that it is not possible to obtain a predictable response time for the execution of a client request. That is, a particular client request could be sitting in a server object's object adapter queue
22
behind a large number of other requests, or, at another time, the particular client request could be the only request in the queue. The client that is waiting for an answer cannot predict when a response will be received from the server object. Another problem is that a very important client request may have to wait behind many not so important requests in the object adapter queue.
These predictability problems dissuade the use of heterogeneous client/server systems to perform distributed processing, leaving such distributed processing to be carried out on homogeneous client/server architectures (such as computer terminals accessing host mainframe computers) especially where a guaran
Freund Thomas
Houston Iain Stuart Caldwell
Burgess Glenton B.
Clay A. Bruce
International Business Machines - Corporation
Kupstas Tod
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