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The EntireX RPC Server under IBM i enables you to call programs as servers, using ILE (Integrated Language Environment).

This document covers the following topics:

• General Rules and Conventions

• Locating and Calling the Target Server

• Configuring the RPC Server

• Scalability of the RPC Server

• Using Internationalization with the RPC Server

• Using SSL or TLS with the RPC Server

• Starting the RPC Server

• Stopping the RPC Server

• Troubleshooting

• Activating Tracing for the RPC Server

General Rules and Conventions

The following rules apply to all server and client applications written in C under IBM i.

• Only ILE (Integrated Language Environment) program objects are supported.

  The EntireX RPC Server does not support OPM (Original Program Model) and EPM (Extended Program Model) objects.

• The servers run in a multithreaded environment. Therefore your application server programs must be thread-safe. This implies that all commands and subprograms accessed in your servers must allow multithreads.

• When linking servers, the binding parameter ACTGRP(*CALLER) must be specified. This guarantees that a server application runs in the same activation group as the calling RPC server. Before processing a server program, the RPC Server verifies if the application was bound with ACTGRP(*CALLER). If not, the RPC Server rejects the call and sends a message to the system operator.

• The IBM i terms "bind" or "binding" are equivalent to the terms "link" or "linking" in the current manual.

• Under IBM i, the term "service program" for a *SRVPGM program is equivalent to "shared library" under UNIX.

Warning: When you compile ILE programs, do not use the PDM source compiling option 14. Use only the ILE commands CRTBNDxxx or CRTxxxMOD with CRTPGM, where xxx denotes the source language such as CBL for COBOL, RPG or CL for command language.

Locating and Calling the Target Server

• Types of Target Server

• Finding a Server Program

• Passing Parameters to the Server

The library and program names that come from the client are used to locate the target server. This two-level IDL concept (library and program) has to be mapped in some way to the RPC Server environment.

Types of Target Server

The RPC Server under IBM i supports target servers as:

• ILE-C applications
  The servers and their stubs are implemented as IBM i service programs of type *SRCPGM, written according to EntireX C Wrapper. ILE-C applications have a two-level concept. The IDL library and program names that come from the client are mapped as follows:

  • The library name is used to form the file names of the target server shared library/object and stub shared library/object

  • The program name is used to form the entry point names for the target server shared library/object and stub shared library/object.

• ILE-RPG, ILE-COBOL and/or ILE-CL applications
  For these applications, the servers are called directly without any stubs. The IDL library and program names that come from the client for this type of target servers are mapped as follows:

  • The library name is used to form the IBM i library name.

  • The program name is used to form the IBM i program name, which is implemented as a bound program of type *PGM.

Under IBM i, the RPC Server uses various methods to call the two kinds of server implementations, depending on the programming language you have used to develop your application. The next section describes how the RPC Server under IBM i distinguishes between the two implementations.

Finding a Server Program

The RPC Server searches for a server in the following order:

First Preference

The RPC Server first assumes that the server was developed in ILE-C. It therefore tries to run two service programs of type *SRCPGM located in the library list of the user who submitted the RPC Server. The service programs represent the shared libraries of:

• the server stub, which is named by default DMy_shared_library and

• the server implementation, named by default My_shared_library, which contains the application functions.

My_shared_library corresponds to the library name in the IDL file. The program names specified in the IDL file are used to form the entry point names, e.g. DCALC and CALC. They represent C functions in the server program. Based on the IDL layout, the sources of the stub and the server frame must be generated from templates using the EntireX Workbench function "Generate C Server" or the corresponding Software AG IDL Compiler command.

Generating C stubs and servers is described in detail under Using the C Wrapper. Extensions specific to IBM i are described under Using the C Wrapper for the Server Side (z/OS, UNIX, Windows, BS2000/OSD, IBM i). You can find an example of a C application server under Step 4: Verify the RPC Server using C.

To locate the target server, the library parameter is also used as a kind of search sequence. See Possible Values for Libraries. The default for the library parameter is set to PREFIX(D) - PREFIX() to be compatible with server stubs and target servers written according to EntireX C Wrapper.

Second Preference

If no appropriate server written in C can be found in the RPC Server job's library list, the RPC Server assumes that the server was developed in ILE-COBOL, ILE-RPG or ILE-CL. It tries to execute a stubless ILE program of type *PGM, where

• the IBM i program name is derived from the IDL program name that comes from the client, and

• the IBM i library name is derived from the IDL library name that comes from the client. Changing the default setting FIX() file gives you control and independence over the library name that comes from the client. You can reroute the call to a target library of your choice (currently restricted to 8-character names) by setting the server parameter Library=FIX(MyLib) in the configuration file of the RPC Server. In this case, the library name sent with the client request is ignored.

See Using EntireX RPC for CL under IBM i for how to use RPC servers in RPG, Using the COBOL Wrapper on how to use RPC servers in COBOL and Using EntireX RPC for CL under IBM i for how to use RPC servers in CL.

You will find an IBM i example of a COBOL application server under Step 3: Verify the RPC Server using COBOL.

If both access approaches fail, an error message is sent back to the client.

Passing Parameters to the Server

The number of Level 01 parameters passed is predetermined by the client and the IDL definition. If this number does not match the number specified in the linkage section of your ILE server program, the operating system will reject the call.

Note:
For stubless access to servers written in ILE-RPG, ILE-COBOL and ILE-CL, currently up to 16 level-01 parameters are supported. More parameters are ignored. Parameter fields of type floating point are not supported.

Configuring the RPC Server

• Configuration File Syntax

• Table of Server Parameters

• runoption

• Possible Values for Endworkers

• Possible Values for Libraries

Configuration File Syntax

• Comments must be on a separate line.

• Comment lines can begin with '*', '/' and ';'.

• Empty lines are ignored.

• Headings in square brackets [topic] are ignored.

• Keywords are not case-sensitive.

Table of Server Parameters

runoption

The runoptions are important for EntireX RPC Servers when the servers are called directly without server stubs, that is on z/VSE Batch, z/OS IMS, CICS, IBM i platforms or with a callable RPC server. When there is no server stub information, it is not known how to align and unmarshal to the target data type (and marshal the data back). With the runoption parameter, it is possible to provide the EntireX RPC Server with such information.

The runoptions are normally set to meet the platform's requirements. In most cases it should not be necessary to modify them.

The runoption keyword can be issued multiple times:

Possible Values for Endworkers

The server is able to adjust the number of worker threads to the current number of client requests. This is configured with the parameter endworkers and several others. See Scalability of the RPC Server for information on how the various parameters work together and what combinations can be specified.

Possible Values for Libraries

The library parameter defines how the RPC Server locates the target server and any stubs on the platform.

The following coding rules apply to the library parameter:

• Up to five library entries can be specified as a sequence.

• Library entries are separated by a hyphen "-".

• Library entries are used from left to right by the RPC Server.

The meaningful combinations vary per platform and the type of target server:

Example: library = PREFIX(D) - PREFIX()

The default for the library parameter is set to satisfy the environment specifics best. Under normal circumstances it is not necessary to change the library parameter.

For an explanation of the approach to locating the target server on your platform, see Locating and Calling the Target Server.

Scalability of the RPC Server

• Parameters

• Configuration Examples

• Suggested Configuration on First Usage

Parameters

The RPC server can be configured to adjust the number of worker threads to the current number of client requests. When more clients are active, more worker threads are needed to achieve the best throughput. Depending on the configuration, worker threads are started on demand and stopped as soon as they are no longer needed.

This mechanism can be configured with the following parameters:

Configuration Examples

• Configuration 1: Medium Lifespan of Worker Threads
• Configuration 2: Shortest Lifespan of Worker Threads
• Configuration 3: Fixed Number of Workers

Configuration 1: Medium Lifespan of Worker Threads

• endworkers=T (timeout)

• timeout=600

• minworkers=1

• maxworkers=10

The endworkers parameter determines the condition under which a worker will be stopped. The value is the period of time specified by the parameter timeout (600 seconds, i.e. 10 minutes). Active workers will be stopped if no client requests arrive within the timeout period, except for the number of threads specified in minworkers.

Minworkers specifies the minimum number of workers that must be available to handle incoming client requests. The server is started (manually) and the first worker (minworkers=1) waits for client requests. When the first client request arrives, a second worker is started. This ensures that there will be at least one free worker (minworkers=1) to handle the next incoming client request.

When the first client request has been worked off (in conversational mode when the conversation has been ended, and in non-conversational mode when the request has been answered), there will be two workers active. For the next incoming client request (second request) no additional worker will be started because the second worker is still free. A third worker will only be started if a third client request arrives before the second request has been finished, in which case there will be three active workers, and so on.

The maxworkers parameter specifies the maximum number of active worker tasks permitted (default is 10).

Configuration 2: Shortest Lifespan of Worker Threads

• endworkers=I (immediately)

• timeout=600

• minworkers=1

• maxworkers=10

In this example the endworkers parameter has been set to "I" (immediately). This setting will stop worker threads immediately when client requests are completed, except for the number of threads specified in minworkers. All other behavior is the same as for Configuration 1: Medium Lifespan of Worker Threads.

Configuration 3: Fixed Number of Workers

• endworkers=N (never)

• timeout=600

• minworkers=10

• maxworkers=

This configuration determines a fixed number of workers. The maxworkers parameter is ignored and the endworkers parameter is set to "N" (never). All worker threads are started immediately with the server and will never stop. This method is useful in minimizing system resources.

Suggested Configuration on First Usage

When you first start using EntireX RPC Server, we suggest the following settings for scaling the server.

Endworkers=T (timeout) and a low value for minworkers is suggested (e.g. minworkers=2). The maxworkers setting depends on the expected maximum number of clients active in parallel (e.g. maxworkers=10). The timeout parameter can be set e.g. to 2 minutes i.e. timeout=120.

Using Internationalization with the RPC Server

It is assumed that you have read the document Internationalization with EntireX and are familiar with the various internationalization approaches described there.

The RPC Server itself does not convert your application data (contained in RPC IDL type A, K, AV and KV fields) received from the broker before giving them to your server application. Conversion or translation is done by the broker according to the codepage the RPC Server tells the broker.

The RPC Server running under IBM i

• does not, by default, send a codepage to the broker as part of the locale string.

• assumes that the broker's locale string defaults match. See Broker's Locale String Defaults. If they do not match, you will have to provide the codepage explicitly.

With the parameter codepage you can

• provide (override) a codepage in the locale string sent to the broker. If a codepage is provided it must follow the rules described under Locale String Mapping.

• force a locale string to be sent if communicating with broker version 7.1.x and below.

The codepage the RPC Server tells the broker must be a codepage supported by the broker, depending on the internationalization approach.

Using SSL or TLS with the RPC Server

This function is not currently supported on this platform.

Starting the RPC Server

Important:
The EntireX RPC Server under IBM i can only be started as a batch job for multithreading reasons. You must use the SBMJOB parameter ALWMLTTHD=*YES to allow multiple threads. Ensure that the subsystem you are submitting to the RPC server allows multiple threads. Use the command WRKJOBD to verify the relevant job description.

To start the RPC Server

1. Ensure that the EntireX product library EXX is in your library list.

2. Create a startup procedure that submits the RPC Server to batch. The RPC Server is called XSERVER (of type *PGM) and is usually located in the EntireX product library EXX.

   The following startup procedure shows the sample procedure STR_RPCSRV that is delivered in the library EXAMPLE:

               PGM                                                                   
   /*------------------------------------------------------------------*/
   /* Example start procedure for the EntireX RPC Server.              */
   /*                                                                  */
   /* Make sure that the RPC Server PGM and the configuration file     */
   /* would be found in the library list.                              */
   /*------------------------------------------------------------------*/
               DCL        VAR(&NULL)   TYPE(*CHAR) LEN(2)  +             
                            VALUE(X'0000')                               
               DCL        VAR(&PARM1)  TYPE(*CHAR) LEN(40) +             
                            VALUE('CFG=*LIBL/QCLSRC(SERVER_CFG)')        
               DCL        VAR(&PARM2)  TYPE(*CHAR) LEN(4)  VALUE('-S')   
   /*------------------------------------------------------------------*/
   /* C-Language binding requires each command-line parameter to be    */
   /* terminated with a NULL character                                 */
   /*------------------------------------------------------------------*/
               CHGVAR     VAR(&PARM1) VALUE(&PARM1 *TCAT &NULL)          
               CHGVAR     VAR(&PARM2) VALUE(&PARM2 *TCAT &NULL)          
   /*------------------------------------------------------------------*/
   SBMJOB     CMD(CALL PGM(*LIBL/XSERVER) +
                              PARM(&PARM1 &PARM2)) + 
                              JOB(RPCSERVER) ALWMLTTHD(*YES)
               SNDPGMMSG  MSG('EntireX RPC Server job submitted to +  
                            batch') MSGTYPE(*COMP)                    
               ENDPGM

   One or two parameters are passed to the RPC server:

   • Parameter 1 specifies the RPC server configuration file (for details see the next step), and

   • The optional parameter 2 "-S", which runs the server in silent mode, that is: no terminal input will be required (e.g. acknowledge error messages). This is recommended for background jobs.

   Note:
   C programming conventions require that each parameter must be terminated with a two-byte hexadecimal zero (variable &NULL in the procedure sample).

3. Create/adjust the RPC server configuration file.

   The IBM i configuration file is derived from the file used for RPC Servers under UNIX. A sample data set is provided in the text member EXAMPLE/QCLSRC(RPCSRV_CFG) delivered with the IBM i installation kit. Edit the individual parameters as described in Configuring the RPC Server. (For the keywords for the server parameter runoption see runoption)

   Most important are the BrokerID=Localhost:1971 of the remote Broker with which you want to register your server, and the ServerName=SRV1 that identifies your service.

   Some parameters are not supported under IBM i (see the comment line in the text member referring to this).

4. Run the startup procedure. Make sure that the configuration file is available in your library list. When the RPC server is up and running, a corresponding entry should appear in the Active Jobs list that can be verified with command WRKACTJOB. If you use the sample procedure described above, the server will be named RPCSERVER as specified in the SBMJOB parameter JOB.

Stopping the RPC Server

To stop the EntireX RPC server

• Use one of the System Management Hub functions Deregister a Service or Deregister a Server. This ensures that deregistration from the Broker is correct.

See also EntireX RPC Server Return Codes.

Troubleshooting

Follow the hints and recommendations given below if the RPC Server does not return the expected results:

• If the client process receives an EntireX error message, read the relevant explanation under Error Messages and Codes.

• Use the command WRKACTJOB to determine whether the RPCSERVER process is still up and running.

• If the RPCSERVER is still running, invoke the job with option 5 (work with ...) and select command 10 to display the job log. Examine the log for system messages and exceptions.

• If the RPCSERVER is no longer active, search for a printed job log in the spooler of the user that submitted the RPC server. Usually, the IBM i system uses the default name QPJOBLOG for the print file.

• For many exceptions, the RPC Server writes messages to the system operator. Use the command WRKMSG MSGQ(*SYSOPR) to query the operator's message queue.

• To monitor the traffic of the RPC Server and to detect problems, restart the RPC Server with tracing activated. To do so, provide a valid log file and enable the tracing with the parameters TraceLevel and TraceDestination in the RPC Server configuration file member. See Activating Tracing for the RPC Server for details.

Activating Tracing for the RPC Server

To switch on tracing for the RPC Server

1. In the RPC Server configuration file, set the parameters TraceLevel and TraceDestination. See Table of Server Parameters.

   See also Starting the RPC Server for information on how to specify the parameters in the RPC Server configuration file under IBM i.

2. Evaluate the return codes. See Error Messages and Codes.

Supported Trace Levels

Trace Destination

To assign a valid log file to the RPC Server

1. Use program EXX/EXACRTLOG to create file LOG in the target library, which is usually your current library.

2. Specify the Trace Destination in the RPC Server configuration file. Trace destination is a generic name including environment variables, e.g., %TEMP%; @PID (process ID), @TID (thread ID), @RANGE[n,m], where m must be greater than n, range is from 0 - 999. Using the RANGE option under IBM i, you can specify the following syntax:

   TraceDestination=MyLib/LOG(MyMember@RANGE[n-m])

   where MyLib is the target library of the file LOG and MyMember is the prefix of the member name. Every time a new RPC Server session has been started, a new log member will be created it the log file.

   Note:
   Under IBM i, a process ID (@PID) is assigned to a session and not changed during session lifetime.

3. When the RPC Server is up and running, use the command WRKACTJOB to verify that the server batch job has opened the log file successfully.

4. To evaluate the return codes, see Error Messages and Codes.

Example

The following excerpt from an RPC server configuration file demonstrates the usage of the Tracelevel and the Tracedestination:

...
 Tracelevel=Support
 TraceDestination=*CURLIB/LOG(RPC@RANGE[1-100])
 ...

When the RPC Server is first started, the member RPC001 will be created in file LOG. The next time, RPC002 will be created and so on.

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