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Diffstat (limited to 'pod/perlguts.pod')
| -rw-r--r-- | pod/perlguts.pod | 73 |
1 files changed, 0 insertions, 73 deletions
diff --git a/pod/perlguts.pod b/pod/perlguts.pod index dce6ca5752..fb52ecfcb7 100644 --- a/pod/perlguts.pod +++ b/pod/perlguts.pod @@ -1252,79 +1252,6 @@ is being used. For a complete description of the PerlIO abstraction, consult L<perlapio>. -=head2 Exception Trapping (JMPENV API) - -As of 5.005, the internal exception trapping mechanism is replaceable -at run-time. - -For a concrete example of usage, see perl.c in the perl source -distribution. Only a general outline is presented here. - -The C<TRYBLOCK()> macro is used to set up a exception handling switch. -C<TRYBLOCK()> takes two arguments. The first argument is a table of -exception handlers: - - struct tryvtbl { - /* [0] executed before JMPENV_POP - [1] executed after JMPENV_POP - (NULL pointers are OK) */ - char *try_context; - void (*try_normal [2]) _((CPERLproto_ void*)); - void (*try_abnormal [2]) _((CPERLproto_ void*)); - void (*try_exception [2]) _((CPERLproto_ void*)); - void (*try_myexit [2]) _((CPERLproto_ void*)); - }; - typedef struct tryvtbl TRYVTBL; - -Each of the functions correspond to the exception types that -are currently supported. The two functions in each array are meant -to be run before and after the exception context is exited, respectively, -via C<JMPENV_POP()>. - -The second argument to C<TRYBLOCK()> is an opaque pointer that is passed -as a first argument to each of the handler functions. This is usually -a structure specific to each particular exception switch containing both -the return value and the arguments to the handler functions. - -Any of the handler function pointers can be C<NULL> except for -C<try_normal[0]>, which is the only thing executed by C<TRYBLOCK()> -after setting up the exception context. Any code executed by -C<try_normal[0]> is free to throw one of the three supported exceptions -using C<JMPENV_JUMP()>. C<JMPENV_JUMP()> can be called with one of the -following values: - - #define JMP_ABNORMAL 1 /* shouldn't happen */ - #define JMP_MYEXIT 2 /* exit */ - #define JMP_EXCEPTION 3 /* die */ - -Control then resumes at the exception switch, which calls the handler -corresponding to the type of exception that was thrown. More exceptions -can be thrown while in the handler, and the process repeats until one of -the handlers return normally. - -In other words, depending on how C<JMPENV_JUMP()> is called, either -C<try_abnormal[0]>, C<try_exception[0]>, or C<try_myexit[0]> are executed. -If C<JMPENV_JUMP()> is invoked yet again before the try handler completes -then execution will B<restart> at the try handler which corresponds to the -most recent C<JMPENV_JUMP()>. Care should be taken to avoid infinite -loops. - -Once the try handler[0] finishes, execution moves on to one of the try -handlers that are run after the exception context is exited (i.e. -handler[1]). However, the difference between the two types of handlers -is that exceptions raised in handlers run after exiting the exception -context are no longer caught by the C<TRYBLOCK()>. Of course, they may -be caught at some outer exception trap set up for the purpose. Therefore, -C<JMPENV_JUMP()> at this point will not be trapped; it will jump to the -previous C<TRYBLOCK()>. This is useful for propagating exceptions to the -top of the stack. - -WARNING: At the time of this writing, the C<CC.pm> compiler backend -does not support exception traps that are configurable at runtime. It -only knows how to handle exceptions thrown with longjmp() (which is what -the default exception mechanism in perl provides). This will be corrected -in a future release. - =head2 Putting a C value on Perl stack A lot of opcodes (this is an elementary operation in the internal perl |