pTAL Conversion Guide

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pTAL Conversion Guide—527302-002

20-9

Comparing Overflow Trapping in Native Processes

A program running as a TNS process can enable or disable overflow traps only by

using overflow trapping block attributes. Each time you enter or exit a block that

specifies a block overflow trapping attribute, your program enables or disables overflow

traps by executing a small number of TNS instructions that set or reset the T bit in the

TNS environment register.

Table 20-1 on page 20-9 shows how the overflow trapping state within a procedure is

affected by:

•

Whether you run your program as a TNS process or a native process

•

Whether the procedure’s caller has enabled or disabled overflow traps

•

Whether you specify overflow trapping by compiler directive, procedure attribute, or

block attribute

Table 20-1 on page 20-9 shows that:

For a native process, the trapping state of a procedure’s caller does not affect the

trapping state in the procedure it calls.

Specifying an overflow trapping attribute on a BEGIN-END block produces the same

trapping state for TNS and native processes, independent of the overflow trapping

state of the code that surrounds the BEGIN-END block.

For a TNS process, the overflow trapping procedure attribute has no effect. (Compare

#3 and #4 in Table 20-1 on page 20-9.)

For a TNS process, the overflow trapping compiler directive determines the trapping

state in the code that follows the outermost BEGIN-END block with an overflow

trapping attribute. (Compare #5 and #6 in Table 20-1 on page 20-9.)

Table 20-2 on page 20-11 shows the changes in the trapping state of code running as

TNS and native processes. Further comments follow Table 20-2 on page 20-11.

Table 20-1. Trapping State Within a Procedure (page 1 of 2)

# Statement Sequence

Process Type

TNS Native

Caller’s

Traps

Enabled

Caller’s

Traps

Disabled

1 ?NOOVERFLOW_TRAPS

PROC p;

BEGIN

...

END;

Enabled

Disabled