This scenario describes the behavior of an application that contains
a PL/I and
a C routine.
Refer to Figure 1 throughout the following
discussion. In this example, a C main
routine invokes a PL/I subroutine.
An exception occurs in the PL/I subroutine.
Figure 1. Stack contents when the PL/I
exception occurs
The actions taken are the following:
- In the enablement step, PL/I determines
if the exception that occurred should be handled as a condition according
to the PL/I rules
of enablement.
- If the exception is to be ignored, control is returned to the
next sequential instruction after where the exception occurred.
- If the exception is to be enabled and processed as a condition,
the condition handling step takes place.
- If a user-written condition handler has been registered on the PL/I stack
frame using CEEHDLR, it is given control. If it issues a resume, the
condition handling step ends. Processing continues in the routine
at the point where the resume cursor points. In this example, no user-written
condition handler is registered for the condition, so the condition
is percolated.
- If an ON-unit has been established for the condition being processed
on the PL/I stack
frame, it is given control. If it issues a GOTO out-of-block, the
condition handling step ends. Execution resumes at the label of the
GOTO. In this example, no ON-unit is established for the condition,
so the condition is percolated.
- If a user-written condition handler has been registered using
CEEHDLR on the C stack
frame, it is given control. If it issues a resume, the condition handling
step ends. Processing continues in the routine to which the resume
cursor points.
Note: There are special considerations for resuming
from some IBM® conditions of
severity 2 or greater. See the chapter on coding a user-written condition
handler in
z/OS Language Environment Programming Guide
for more
information.
In this example, no user-written condition
handler is registered for the condition, so the condition is percolated.
- If a C signal
handler has been registered for the condition, it is given control.
If it successfully issues a resume or a call to longjmp(),
the condition handling step ends. Processing resumes in the routine
to which the resume cursor points.
In this example no C signal
handler is registered for the condition, so the condition is percolated.
- What happens next depends on whether the condition is promotable
to the PL/I ERROR
condition. The following can happen:
- If the condition is not promotable to the PL/I ERROR
condition, then the Language Environment default
actions take place, as described in Table 1. Condition handling
ends.
- If the PL/I default
action for the condition is to promote it to the PL/I ERROR
condition, the condition is promoted, and another pass of the stack
is made to look for ERROR ON-units or user-written condition handlers.
If an ERROR ON-unit or user-written condition handler is found, it
is invoked.
- If either of the following occurs:
- An ERROR ON-unit or user-written condition handler is found, but
it does not issue a GOTO out of block or similar construct
- No ERROR ON-unit or user-written condition handler is found
then the ERROR condition is promoted to T_I_U (Termination Imminent
due to an Unhandled condition). Condition handling now enters the
termination imminent step. Because T_I_U maps to the PL/I FINISH
condition, a FINISH ON-unit is run if the stack frame in which it
is established is reached.
- If no condition handler moves the resume cursor and issues a resume, Language Environment terminates
the thread.