HP OpenVMS Systems Documentation
Example 1-6 assumes that the logical COBOLPATH is set as follows:
$ define COBOLPATH MYDEV:[MYDIR]
When you execute the following command line:
$ MYPROG 1028 powers.dat
The following will result:
For additional information, refer to the ACCEPT and DISPLAY statements
in the HP COBOL Reference Manual. <>
126.96.36.199 Accessing Input and Output Devices at Run Time
ACCEPT and DISPLAY statements may interact with the input and output
devices by referring to them through the environment variables
COBOL_INPUT and COBOL_OUTPUT, respectively. See Chapter 11 for more
188.8.131.52 Debugging Environment
RUN [/[NO]DEBUG] file-spec
In the preceding syntax format, file-spec is the name of the executable image to be run. A typical example would be:
$ RUN /DEBUG MYPROG
In this example, MYPROG is the name of the executable image to be run. You would specify the /DEBUG qualifier to invoke the OpenVMS Debugger if the image was not linked with it. You cannot use /DEBUG on images linked with the /NOTRACEBACK qualifier. If the image (in this case, MYPROG) was linked with the /DEBUG qualifier and you do not want the debugger to prompt you, use the /NODEBUG qualifier. The default action depends on whether or not the file was linked with the /DEBUG qualifier.
Using the /DEBUG qualifier with the RUN command does not produce symbol table information if you did not specify the /DEBUG qualifier when you compiled and linked your program.
The following example executes the image MYPROG.EXE without invoking the debugger:
$ RUN MYPROG/NODEBUG
During execution, an image can generate a fatal error called an exception condition. When an exception condition occurs, the system displays a message. Run-time messages can also be issued by the OpenVMS system or by other utilities such as SORT. Other kinds of errors that can occur at run time include program run errors and run-time input/output errors.
%COBThe program name of the HP COBOL Run-Time Library. This prefix indicates a run-time message.
sThe severity of the error. As with messages from the compiler and the linker, the severity indicator can be F (Fatal), E (Error), W (Warning), or I (Informational).
identThe message identification. This is a descriptive abbreviation of the message text.
message-textThe run-time message. This portion may contain more than one line of output. A message generally provides you with enough information to determine the cause of the error so that you can correct it.
%COB-E-DIVBY-ZER, divide by zero; execution continues
Both the compiler and the OpenVMS Run-Time Library include facilities for detecting and reporting errors. You can use the OpenVMS Debugger and the traceback facility to help you locate errors that occur during program execution. For a description of HP COBOL run-time messages, use the HELP COBOL Run-Time Messages command.
Faulty program logic can cause abnormal termination. If errors occur at run time, the Run-Time Library (RTL) displays a message with the same general format as system error messages. In addition, the system traceback facility displays a list of the routines that were active when the error occurred.
When an error occurs, TRACEBACK produces a symbolic dump of the active call frames. A call frame represents one execution of a routine. For each call frame, TRACEBACK displays the following information:
You can also use the OpenVMS Debugger to examine the machine code instruction. To do this, compile and link the program using the /DEBUG qualifier. When you run the program, you automatically enter the debugger. Once in the debugger, you could use the EXAMINE/INSTRUCTION command to examine the contents of the failed instruction. You could also use the debugger in screen mode, which would indicate where the error occurred.
For more information about the OpenVMS Debugger, refer to Appendix C
and the OpenVMS Debugger Manual.
1.3 HP COBOL and Alpha and I64 Architecture System Resources
For many user applications, the HP COBOL compiler requires
significantly more system resources than HP COBOL for OpenVMS VAX. In fact, unless
you have adjusted your system resource parameters accordingly, the
attempt to compile may fail because of insufficient virtual memory.
Also, for very large programs (greater than 10,000 lines), you might
experience extremely long compile times. Knowing why HP COBOL
requires more memory can help you take actions to avoid resource
1.3.1 Compilation Performance
The Alpha and I64 architectures are RISC (reduced instruction set computer) architectures. Many other processor architectures, including the VAX, are CISC (complex instruction set computer) architectures. The main distinguishing characteristic of a RISC machine is that it has few instructions and each instruction does a small amount of work. A CISC machine generally has many instructions, most of which perform many complicated operations in one step.
By reducing the amount of work that is done in each instruction (and by reducing the number of instructions), the complexity of the hardware is reduced. These hardware changes, plus others, result in an increase in the number of instructions per second that can be completed. The result is much faster overall system performance.
A tradeoff of RISC systems is that compilers for these architectures generally must do a great deal more work than a corresponding compiler for a CISC architecture. For example, the compiler must compute the best way to use all of the functional units of the processor, and it must determine how to make the best use of registers and on-chip data cache because reads and writes to main memory are generally slow compared to the speed of the processor.
The code generation portion of the HP COBOL for OpenVMS VAX compiler was developed for the CISC architecture of the VAX. The compiler examines one COBOL statement at a time, determines the VAX instructions to be constructed to execute that statement, and then moves on to the next one. Subsequently it uses "Peephole" optimization to enhance the performance of the generated machine code.
On the other hand, the HP COBOL compiler was developed for the Alpha and I64 architectures. It is a globally optimizing compiler based on the most recent compiler technology. It does many optimizations including Peephole, loop unrolling, and instruction pipelining. Also, the compiler uses mathematical graph theory to construct an internal representation of the entire COBOL program, and it repeatedly traverses this structure at compile time, to produce the most efficient machine code for the program. This results in very high performance code, to the benefit of your users at run time. Although the HP COBOL compiler on OpenVMS Alpha and I64 requires more resources than some other compilers to do this additional work at compile time, this cost is offset by better performance during the many run times that follow.
To reduce the impact on system resources at compile time, do the following:
Large arrays (tables) can have a significant impact on compile time and resource requirements. In addition to the size of the program source, you should also examine the amount of space allocated in your Data Division, particularly for arrays. The number of array elements as well as the size of the array elements is significant. This impact can be minimized in two ways: by system tuning (as suggested in this section), which will optimize system resources for the compile, and by using INITIALIZE instead of VALUE in your data definitions, which will improve compilation performance.