Guardian Procedure Calls Reference Manual

If you are using the Safeguard product, this security information might not apply.
• Tape file open—access mode
The file system does not enforce read-only or write-only access for unlabeled tape, even though
no error is returned if you specify one of these access modes when opening a tape file.
• File open—exclusion and access mode checking
When a file open is attempted, the requested access and exclusion modes are compared with
those of any opens already granted for the file. If the attempted open is in conflict with other
opens, the open fails with error 12.
Figure 8 lists the possible current modes and requested modes, indicating whether an open
succeeds or fails.
NOTE: Protected exclusion mode has meaning only for disk files. For other files, specifying
protected exclusion mode is equivalent to specifying shared exclusion mode.
Figure 8 Exclusion and Access Mode Checking
• Applications with large receive-depth values
If you have applications that use large receive-depth values, you must periodically monitor
their Message Quick Cell (MQC) usage levels using the PEEK /CPU N/ MQCINFO command
in all the processors to make sure that the total amount of memory allocated for MQCs does
not approach the per-processor memory limit for MQCs. This limit is 128 MB in H06.19 /
J06.08 and earlier RVUs, and 1 GB in H06.20 / J06.09 and later RVUs. For more information,
see Table 54 (page 1580).
If you run applications with very large receive-depth values on systems running H06.19/J06.08
or earlier RVUs, you must consider upgrading to H06.20/J06.09 or a later RVU if you notice
MQC memory usage levels approach the per-processor memory limit of 128 MB. To determine
the amount of memory used for MQCs by CPU N from the PEEK /CPU N/ MQCINFO
command output, add the page counts for all MQC sizes, and then multiply the total page
count allocated for MQCs by the page size (16 KB).
904 Guardian Procedure Calls (O)