In the architecture of modern e-business applications (such as SOA), loosely coupled systems are becoming more and more important. Reliable messaging is one important technology for this type of system.
Reliable RPC is the EntireX implementation of a reliable messaging system. It combines EntireX RPC technology and persistence, which is implemented with units of work (UOWs).
Reliable RPC allows asynchronous calls ("fire and forget")
Reliable RPC is supported by most EntireX wrappers
Reliable RPC messages are stored in the Broker's persistent store until a server is available
Reliable RPC clients are able to request the status of the messages they have sent
Reliable RPC is used to send messages to a persisted Broker service. The
messages are described by an IDL program that contains only IN parameters. The
client interface object and the server interface object are generated from this
IDL file, using the EntireX COBOL Wrapper.
Reliable RPC is enabled at runtime. The client has to set one of two different modes before issuing a reliable RPC request:
AUTO_COMMIT
CLIENT_COMMIT
While AUTO_COMMIT commits each RPC message implicitly after sending it, a
series of RPC messages sent in a unit of work (UOW) can be committed or rolled
back explicitly using CLIENT_COMMIT mode.
The server is implemented and configured in the same way as for normal RPC.
The following steps describe how to write a COBOL reliable RPC client program with the scenario Using the COBOL Wrapper for CICS with DFHCOMMAREA Calling Convention (z/OS and z/VSE) and Linkage access to RPC communication.
Reliable RPC requires an explicit broker logon. See Using Broker Logon and Logoff.
For every program definition in the Software AG IDL file, the templates will generate a copybook file that describes the customer data of the interface as a COBOL structure. For ease of use, the copybook can be embedded into the RPC client program.
However, if more appropriate, customer data structures can be used. In this case the COBOL data types and structures must match the interfaces of the generated client interface objects, otherwise unpredictable results will occur.
* Declare the customer data of the generated RPC interface
01 SENDMAIL.
02 SM-COMA.
03 SM-TOADDRESS PIC X(60).
03 SM-SUBJECT PIC X(20).
03 SM-TEXT PIC X(100).
The RPC communication area must be declared and initialized in your RPC client program as follows:
* Declare RPC communication area
02 ERX-COMMUNICATION-AREA.
COPY ERXCOMM.
. . . . . .
* Initialize RPC communication area
INITIALIZE ERX-COMMUNICATION-AREA.
MOVE "2000" to COMM-VERSION.
The following settings to the RPC communication area are required as a minimum to use the COBOL Wrapper. These settings have to be applied in your RPC client program. It is not possible to generate any defaults into your client interface objects:
* assign the broker to talk with MOVE "localhost:1971" to COMM-ETB-BROKER-ID. * assign the server to talk with MOVE "RPC" to COMM-ETB-SERVER-CLASS. MOVE "SRV1" to COMM-ETB-SERVER-NAME. MOVE "CALLNAT" to COMM-ETB-SERVICE-NAME. * assign the user ID for Broker logon MOVE "ERXUSER" to COMM-USERID. MOVE "PASSWORD" to COMM-PASSWORD.
MOVE "LO" TO COMM-FUNCTION.
EXEC CICS LINK
PROGRAM ("COBSRVI")
COMMAREA (ERX-COMMUNICATION-AREA)
LENGTH (LENGTH OF ERX-COMMUNICATION-AREA)
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
END-EXEC.
Check whether the logon call was successful or not.
Before reliable RPC can be used, the reliable state must be set to
either ERX_RELIABLE_CLIENT_COMMIT or ERX_RELIABLE_AUTO_COMMIT.
"C" - CLIENT_COMMIT
"A" - AUTO_COMMIT
* Set the reliable RPC mode MOVE "C" TO COMM-RELIABLE-STATE.
The RPC message is sent using the EXEC CICS LINK interface.
* Send the RPC message
MOVE DFHRESP(NORMAL) TO CICS-RESP1.
MOVE DFHRESP(NORMAL) TO CICS-RESP2.
MOVE ZEROES TO COMM-RETURN-CODE.
EXEC CICS LINK
PROGRAM ("SENDMAIL")
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
COMMAREA (SENDMAIL)
LENGTH (LENGTH OF SENDMAIL)
END-EXEC.
When the RPC message is returned, it needs to be checked whether it was successful or not:
IF COMM-RETURN-CODE IS = ZERO
Perform success-handling
ELSE
Perform error-handling
END-IF.
The field COMM-RETURN-CODE in the RPC communication area contains the error provided by the COBOL Wrapper. For the error messages returned, see Error Messages and Codes.
Note:
After successful call (Step 6a) the UOWID is available in the RPC
communication area field COMM-ETB-UOW-ID. See The RPC Communication Area (Reference).
To determine that reliable RPC messages are delivered, the reliable RPC message status can be queried. See Understanding UOW Status and Broker UOW Status Transition for more information.
MOVE DFHRESP(NORMAL) TO CICS-RESP1.
MOVE DFHRESP(NORMAL) TO CICS-RESP2.
MOVE "RS" TO COMM-FUNCTION.
MOVE ZEROES TO COMM-RETURN-CODE.
EXEC CICS LINK
PROGRAM ("COBSRVI")
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
COMMAREA (ERX-COMMUNICATION-AREA)
LENGTH (LENGTH OF ERX-COMMUNICATION-AREA)
END-EXEC.
Note:
After successful call the UOW status is available in the RPC
communication area field COMM-RELIABLE-STATUS. See The RPC Communication Area (Reference).
Check whether the check status call was successful or not.
Send a second reliable RPC message. See Step 6a and Step 6b.
Check the reliable RPC message before the commit call. See Step 7a and Step 7b.
Now both reliable RPC messages are committed. This will deliver all reliable RPC messages to the server if it is available.
MOVE DFHRESP(NORMAL) TO CICS-RESP1.
MOVE DFHRESP(NORMAL) TO CICS-RESP2.
MOVE "RC" TO COMM-FUNCTION.
MOVE ZEROES TO COMM-RETURN-CODE.
EXEC CICS LINK
PROGRAM ("COBSRVI")
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
COMMAREA (ERX-COMMUNICATION-AREA)
LENGTH (LENGTH OF ERX-COMMUNICATION-AREA)
END-EXEC.
Check whether the commit call was successful or not.
Send a third reliable RPC message. See Step 5a and Step 5b.
Check the reliable RPC message before the rollback call. See Step 6.
Roll back the current reliable RPC message.
MOVE DFHRESP(NORMAL) TO CICS-RESP1.
MOVE DFHRESP(NORMAL) TO CICS-RESP2.
MOVE "RR" TO COMM-FUNCTION.
MOVE ZEROES TO COMM-RETURN-CODE.
EXEC CICS LINK
PROGRAM ("COBSRVI")
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
COMMAREA (ERX-COMMUNICATION-AREA)
LENGTH (LENGTH OF ERX-COMMUNICATION-AREA)
END-EXEC.
When the rollback call is returned, check whether it was successful or not. If the rollback call failed, an explicit EOC needs to be sent:
MOVE DFHRESP(NORMAL) TO CICS-RESP1.
MOVE DFHRESP(NORMAL) TO CICS-RESP2.
MOVE "RS" TO COMM-FUNCTION.
MOVE ZEROES TO COMM-RETURN-CODE.
EXEC CICS LINK
PROGRAM ("COBSRVI")
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
COMMAREA (ERX-COMMUNICATION-AREA)
LENGTH (LENGTH OF ERX-COMMUNICATION-AREA)
END-EXEC.
MOVE "LF" TO COMM-FUNCTION.
EXEC CICS LINK
PROGRAM ("COBSRVI")
COMMAREA (ERX-COMMUNICATION-AREA)
LENGTH (LENGTH OF ERX-COMMUNICATION-AREA)
RESP (CICS-RESP1)
RESP2 (CICS-RESP2)
END-EXEC.
Check whether the logoff call was successful or not.
There are no server-side methods for reliable RPC. The server does not send back a message to the client. The server can run deferred, thus client and server do not necessarily run at the same time. If the server fails, it returns an error code greater than zero. This causes the transaction (unit of work inside the Broker) to be cancelled, and the error code is written to the user status field of the unit of work. For writing reliable RPC servers, see Using the COBOL Wrapper for the Server Side.
To execute a reliable RPC service with an RPC server:
the parameter logon must be set to "YES", see
the parameter LOGN must be set to "YES",
see Configuring the RPC Server.
A Broker configuration with PSTORE is recommended. This enables the Broker
to store the messages for more than one Broker session. These messages are
still available after Broker restart. The attributes
STORE, PSTORE,
and PSTORE-TYPE in the Broker attribute file can
be used to configure this feature. The lifetime of the messages and the status
information can be configured with the attributes
UWTIME and
UWSTAT-LIFETIME. Other attributes such as
MAX-MESSAGES-IN-UOW,
MAX-UOWS and
MAX-UOW-MESSAGE-LENGTH may be used in addition
to configure the units of work. See Broker Attributes.
The result of the generic RPC function call "RS" - get reliable status depends on the
configuration of the unit of work status lifetime in the EntireX Broker
configuration. See COMM-FUNCTION. If the status is not stored longer than the message, the
function call returns the error code 00780305 (no matching UOW
found).