Exception occurs in PL/I

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 exception occurs in PL/I

The actions taken are the following:

1. 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, described below, takes place.
2. Is 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.
3. 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.
4. 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 user-written condition handlers in z/OS Language Environment Programming Guide.

   In this example, no user-written condition handler is registered for the condition, so the condition is percolated.

5. 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.

6. 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.