CRE Programmer's Guide

CRE Services
Common Run-Time Environment (CRE) Programmer’s Guide—528146-004
2-18
Sharing Standard Files Using the CRE
might write to the same disk location because there is no method for the run-time
libraries to share the file record pointer. That is, because each routine begins writing at
the beginning of the same file, the first record written by each of the program’s routines
writes to the same disk location—thereby overwriting data already written there by
another routine in the same program.
Figure 2-1 on page 2-18 is an example of a mixed-language TNS program that has
COBOL, TAL, and C routines, and does not run in the CRE. The main routine is written
in COBOL. The C and COBOL run-time libraries call system procedures to access a
file. Because the TAL library does not provide support for input or output, TAL routines
must send I/O requests directly to the NonStop operating system.
Sharing Standard Files Using the CRE
For Guardian programs that run in the CRE, I/O requests to standard input, standard
output, and standard log are processed by the language-specific run-time library for the
requesting routine. However, the run-time library requests system services by calling
CRE library functions rather than by calling system procedures directly. If the CRE
receives a request to open a standard file that it has not opened at the operating
system level, it calls the FILE_OPEN_ system procedure to open the file. Having
opened the file, the CRE grants a connection—a path—to the same file open for each
additional request that the CRE receives to open the same standard file. The CRE
coordinates requests for new connections and requests to release previously granted
connections. With the CRE, the standard files belong to a program as a whole, rather
than to any one routine or run-time library of a program.
Figure 2-1. A C-Series Mixed-Language Process
C Run-Time Library
201VST .VSD
$VOL
SUBVOL.FILE
0
1
2
3
COBOL:
TAL:
C:
COBOL Run-Time Library
NonStop Operating System