The stack frame model
A stack consists of an ordered set of stack elements, called stack frames, which are managed in a last-in first-out manner. Unqualified references to stack mean invocation stack. The invocation stack can contain multiple invocation stack frames, which represent invocation instances of routines. A stack frame is added to the stack on entry to a routine and removed from the stack on exit from the routine.
The Language Environment condition handling model is based on stack frames, in which condition handling can be different in different stack frames. Another condition handling model is global condition handling, which means that one condition handling mechanism remains in effect for the life of an application. The distinction between global condition handling and condition handling within a stack frame-based model can affect how a condition is handled in your application, particularly if it is a mixed-language application.
- A function call in C or C++ that has not been inlined
- Entry into a program in COBOL
- Entry into a main program or subprogram in Fortran
- Entry into a procedure or begin block in PL/I
- Entry into an ON-unit in PL/I
A stack frame is added to the stack every time a new routine is entered and removed when it is exited. Language Environment uses stack frames to keep track of such things as the routine currently executing, the point at which an error occurs, and the point at which execution should resume after the condition is handled.
Each new stack frame can contain user-written condition handlers registered with CEEHDLR, but language-specific handlers such as C/C++ signal handlers are not associated with each stack frame. User condition handlers can be unregistered explicitly (by calling CEEHDLU) or implicitly, as when the routine that registered the handler returns control to its caller.
Two cursors, or pointers, keep track of the state of condition handling. The cursors are named the handle and resume cursors.