Ü Static binding & Dynamic binding


We should be aware of the binding concept before we proceed with Service program.

·         Dynamic binding means that neither program knows about the other until the call takes place. In that sense it is dynamic, because all the binding is happening right at the time the program is called. Whenever you call one program from another using the CALL operation, you are dynamically binding those programs.


·         Static binding, on the other hand, is the method of binding two objects together well before they ever use each other. This type of binding is static, in that the objects are bound together and the relationship between those bound objects remains consistent.


Static binding Vs. Dynamic binding

·         In dynamic binding if we have more modules, there will be more time to do program call resolution and program startup tasks.

·         If we don’t go for modularity then there won’t be any overhead for program call resolution and program startup tasks, but to maintain a single big program is not an easy task.



Ü Modules


Module is another concept that is used in Service program.


·         Modules allow you to organize related tasks into smaller units of code, which can then be bound together into programs or service programs.

·         They cannot be called using the dynamic CALL operation but are, instead, called with either the bound call (CALLB in RPG) or a prototyped call (CALLP in RPG).

·         NOMAIN modules cannot be called directly. Instead, the subprocedures contained inside the module are called using prototyped call (CALLP in RPG).



Ü Service program


Service Program (*SRVPGM) can be viewed as a collection of subroutines packaged together and accessible to the outside world. You use the CRTSRVPGM command to create a service program.



Ü Procedures (or subprocedures)


Procedures (also known as subprocedures) are the smallest component of static binding.



Ü Types of Static binding


There are two types of static binding: Bind by copy and bind by reference.


¤  Bind by copy is accomplished by copying two or more modules into a program.


Columns . . . :    6  76            Edit                        AMIT/QRPGLESRC
SEU==>                                                                 MODULE1
FMT H  HKeywords++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*************** Beginning of data *************************************
0002.00 DVAR1             S              5  0 EXPORT  INZ(11111)
0003.00 DVAR2             S              5  0 IMPORT
0003.03 C                   CALLB     'MODULE2'
0003.04 C                   EVAL      VAR1=VAR2 +33333  >>>>>>>>>>>>>>>   VAR2=55555
0005.00 C     VAR1          DSPLY
0006.00 C                   SETON                                        LR
****************** End of data ****************************************


 Columns . . . :    6  76            Edit                        AMIT/QRPGLESRC
 SEU==>                                                                 MODULE2
 FMT D  DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++
        *************** Beginning of data *************************************
0002.00 DVAR1             S              5  0 IMPORT                           
0003.00 DVAR3             S              5  0 IMPORT                           
0003.07 DVAR2             S              5  0 EXPORT                           
0003.08 C                   CALLB     'MODULE3'                                
0004.00 C                   EVAL      VAR2=VAR1+VAR3   >>>>>>>>>>>>>>>   VAR2=22222
0005.00 C                   RETURN                                             
        ****************** End of data ****************************************       

Columns . . . :    6  76           Browse                       AMIT/QRPGLESRC
SEU==>                                                                 MODULE3
FMT D  DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++
*************** Beginning of data *************************************
0002.00 DVAR3             S              5  0 EXPORT
0004.00 C                   EVAL      VAR3=11111     >>>>>>>>>> VAR3=11111 (NOT 10101)
0004.01 C                   RETURN
0004.02 C                   EVAL      VAR3=10101     >>>>>>>>>> Control doesn’t reach here
****************** End of data ****************************************









Notice that MODULE1 actually calls the other two modules, using the CALLB operation. That's because the MODULE1 module was made the program entry procedure (PEP) by the ENTMOD parameter in the CRTPGM command.




¤  Bind by reference works a little differently. Modules are still bound together to form an object, but this time the object is a service program (*SRVPGM), not a program.


  • There exists only one copy of the code, but that copy is loaded at runtime and shared with other programs or service programs that might need it.


  • A service program is not all that different from a program, except that each module contains one or more subprocedures and those subprocedures, not the modules, are the entry points into the service program.


  • One of the beauties of service programs is that they have multiple entry and exit points.


  • You can think of a service program as many subroutines bunched together and made available to the outside world.


  • Another thing is that the modules contained in service programs contain no program entry procedure (PEP), as our program did. This is accomplished by adding an H-spec (NOMAIN) entry in each module.


  • NOMAIN states that there is no PEP, and therefore much of the tasks done at program startup, including the loading of the logic cycle, are not done. This lightens the object significantly.


  • It also means that in addition to the service program not being able to be called directly, the modules can't be called, either.


  • The only way to access the service program is through the subprocedures. The module becomes little more than a container for its subprocedures.



Create and use the service program (Bind by reference)


Columns . . . :    6  76           Browse                       AMIT/QRPGLESRC
 SEU==>                                                              MODULE_IFC
 FMT H  HKeywords++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        *************** Beginning of data *************************************
0000.01 HNOMAIN                                                                
0000.02  *                                                                     
0000.03 DPROC1            PR                                                    
0000.04 DPROC2            PR                                                   
0000.05 DPROC3            PR                                                   
0000.06 PPROC1            B                   EXPORT                           
0000.07 DPROC1            PI                                                   
0000.08 C     'PROCEDURE1'  DSPLY                                              
0000.09 PPROC1            E                                                    
0000.10  *                                                                     
0000.11 PPROC2            B                   EXPORT                           
0000.12 DPROC2            PI                                                   
0000.13 C     'PROCEDURE2'  DSPLY                                              
0000.14 PPROC2            E                                                    
0001.00  *                                                                      
0003.00 PPROC3            B                   EXPORT 
0004.00 DPROC3            PI                                                   
0005.00 C     'PROCEDURE3'  DSPLY                                               
0006.00 PPROC3            E                                                    
        ****************** End of data ****************************************



Now create Service program SRVPGM1:






¤  Points to remember here:

·         These are three entry points here into this module, meaning that any of these 3 subprocedures can be called from outside this module, provided we define them to be exported.

·         The EXPORT (*ALL) parameter tells which subprocedures you want to make available to the outside world.

·         If a module is going to be called by one program and one program only, use bind by copy. It is the best overall performer in this case, because the code is copied right into the program at compile time.

·         However, this becomes a potential maintenance and compile nightmare if we decide to use bind by copy and the module is going to be called by many programs. In that case it is better to go for bind by reference.



 Columns . . . :    6  76           Browse                       AMIT/QRPGLESRC
 SEU==>                                                              CALLSRVPGM
 FMT H  HKeywords++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        *************** Beginning of data *************************************
0001.00 HOPTION(*NODEBUGIO)                                                    
0001.01 DPROC1            PR                                                   
0001.02 DPROC2            PR                                                   
0001.03 DPROC3            PR                                                   
0003.03 C                   CALLP     PROC1                                    
0003.04 C                   CALLP     PROC2                                    
0003.05 C                   CALLP     PROC3                                    
0003.06 C                   movel     1             i                 1 0      
0006.00 C                   SETON                                        LR    
        ****************** End of data ****************************************



Now bind the service program SRVPGM1 to the calling program CALLSRVPGM:










Ü Advantages of service programs

  • They do not take up auxiliary storage space. There is only one copy for all users.
  • There is only a single copy of the read-only code in main storage for all users in this service program is the same as a program that you call dynamically.
  • Each user of the service program has an independent work area.
  • You can pass parameters to a service programs by using the traditional parameter list (or) by importing and exporting variables.
  • Service programs can be maintained independently of the programs that use the functions. In most cases, changing a service programs does not cause a program using the function to be changed or re-created.


Ü Disadvantages of service programs

·         Service programs are less desirable for a function you may or may not need. The reason is that it is slower to call a main program that refer to a service program




Ü Subprocedures: Better than Subroutines


Subroutines have their limitations, two of which are:

·         The first is that subroutines use global variables only. That is, any variable or constant or indicator that I use in a subroutine may be used anywhere else in the program--in the main calculations, in any subroutine, in output specs. This can lead to undesirable side effects.

·         The other thing that bothers me is that I can't define parameters to pass data to subroutines.

·         Subroutines are faster than subprocedures. I have never had to worry about the performance of subprocedures, but in a heavily used program, performance may become an issue. Using subroutines instead of subprocedures may make a difference.


Ü Binding directory


When you create a program or service program, you can list the modules for the program



Or you can list them in a “binding directory”



Binding directory listing modules to create a program

A binding directory is just a list, containing modules and/or/service programs.



Specifying the service programs when creating a pgm



***Note: If the system finds that one of the modules for the program wants to call procedure “proc1”, it will search for that procedure in the modules or service programs listed in the MODULE, BNDSRVPGM or BNDDIR parameters of the command.


                             Create Program (CRTPGM)                           
 Type choices, press Enter.                                                    
 Program  . . . . . . . . . . . . > CALLSRVPGM    Name                         
   Library  . . . . . . . . . . .     *CURLIB     Name, *CURLIB                
 Module . . . . . . . . . . . . .   *PGM          Name, generic*, *PGM, *ALL   
   Library  . . . . . . . . . . .                 Name, *LIBL, *CURLIB...      
                + for more values                                              
 Text 'description' . . . . . . .   *ENTMODTXT                                 
                            Additional Parameters                              
 Program entry procedure module     *FIRST        Name, *FIRST, *ONLY, *PGM    
   Library  . . . . . . . . . . .                 Name, *LIBL, *CURLIB...      
 Bind service program . . . . . .   *NONE         Name, generic*, *NONE, *ALL   
   Library  . . . . . . . . . . .                 Name, *LIBL                  
                + for more values                                           
 Binding directory  . . . . . . .   *NONE         Name, *NONE                  
   Library  . . . . . . . . . . .                 Name, *LIBL, *CURLIB...      
                + for more values                                                 
 Activation group . . . . . . . .   *CALLER       Name, *ENTMOD, *NEW, *CALLER 





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