Exception occurs in C

This scenario describes the behavior of an application that contains a C and a PL/I routine. Refer to Figure 1 throughout the following discussion. In this scenario, a PL/I main routine invokes a C subroutine. An exception occurs in the C subroutine.

Figure 1. Stack contents when the exception occurs in C
The figure shows the contents of the stack when the exception occurs in C.

The actions taken are the following:

  1. In the enablement step, it is determined whether the exception in the C routine should be enabled and treated as a condition. If any of the following are true, the exception is ignored, and processing continues at the next sequential instruction after where the exception occurred:
    • You specified SIG_IGN for the exception in a call to signal().
      Note: The system or user abend corresponding to the signal(SIGABND) or the Language Environment message 3250 is not ignored. The enclave is terminated.
    • The exception is one of those listed as masked in Table 2, and you have not enabled it using the CEE3SPM callable service.
    • You did not specify any action, but the default action for the condition is SIG_IGN (see Table 2).
    • You are running under CICS® and a CICS handler is pending.
    If you did none of these things, the condition is enabled and processed as a condition.
  2. If a user-written condition handler has been registered on the stack frame using CEEHDLR, 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.

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

  3. If a C signal handler has been registered for the condition on the C stack frame, 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 case, there is not a C signal handler registered for the condition.

  4. The condition is still unhandled. If C does not recognize the condition, or if the C default action (listed in Table 2) is to terminate, the condition is percolated.
  5. 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.
  6. 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.
  7. 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 is made of the stack 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 or user-written condition handler is run if the stack frame in which it is established is reached.
    • If no condition handler moves the resume cursor and issued a resume, Language Environment terminates the thread.
Parent topic: C to PL/I condition handling