struct backtrace *backtrace_list;
+/* This structure helps implement the `catch' and `throw' control
+ structure. A struct catchtag contains all the information needed
+ to restore the state of the interpreter after a non-local jump.
+
+ Handlers for error conditions (represented by `struct handler'
+ structures) just point to a catch tag to do the cleanup required
+ for their jumps.
+
+ catchtag structures are chained together in the C calling stack;
+ the `next' member points to the next outer catchtag.
+
+ A call like (throw TAG VAL) searches for a catchtag whose `tag'
+ member is TAG, and then unbinds to it. The `val' member is used to
+ hold VAL while the stack is unwound; `val' is returned as the value
+ of the catch form.
+
+ All the other members are concerned with restoring the interpreter
+ state. */
struct catchtag
{
Lisp_Object tag;
is handled by the command loop's error handler. */
int debug_on_quit;
-/* Nonzero means we are trying to enter the debugger.
- This is to prevent recursive attempts. */
-int entering_debugger;
+/* The value of num_nonmacro_input_chars as of the last time we
+ started to enter the debugger. If we decide to enter the debugger
+ again when this is still equal to num_nonmacro_input_chars, then we
+ know that the debugger itself has an error, and we should just
+ signal the error instead of entering an infinite loop of debugger
+ invocations. */
+int when_entered_debugger;
Lisp_Object Vdebugger;
Vquit_flag = Qnil;
debug_on_next_call = 0;
lisp_eval_depth = 0;
- entering_debugger = 0;
+ when_entered_debugger = 0;
}
Lisp_Object
if (specpdl_size + 40 > max_specpdl_size)
max_specpdl_size = specpdl_size + 40;
debug_on_next_call = 0;
- entering_debugger = 1;
+ when_entered_debugger = num_nonmacro_input_chars;
return apply1 (Vdebugger, arg);
}
return c.val;
}
-/* Discard from the catchlist all catch tags back through CATCH.
- Before each catch is discarded, unbind all special bindings
- made within that catch. Also, when discarding a catch that
- corresponds to a condition handler, discard that handler.
+/* Unwind the specbind, catch, and handler stacks back to CATCH, and
+ jump to that CATCH, returning VALUE as the value of that catch.
- At the end, restore some static info saved in CATCH.
+ This is the guts Fthrow and Fsignal; they differ only in the way
+ they choose the catch tag to throw to. A catch tag for a
+ condition-case form has a TAG of Qnil.
- This is used for correct unwinding in Fthrow and Fsignal,
- before doing the longjmp that actually destroys the stack frames
- in which these handlers and catches reside. */
+ Before each catch is discarded, unbind all special bindings and
+ execute all unwind-protect clauses made above that catch. Unwind
+ the handler stack as we go, so that the proper handlers are in
+ effect for each unwind-protect clause we run. At the end, restore
+ some static info saved in CATCH, and longjmp to the location
+ specified in the
+
+ This is used for correct unwinding in Fthrow and Fsignal. */
static void
-unbind_catch (catch)
+unwind_to_catch (catch, value)
struct catchtag *catch;
+ Lisp_Object value;
{
register int last_time;
+ /* Save the value in the tag. */
+ catch->val = value;
+
+ /* Restore the polling-suppression count. */
+ if (catch->poll_suppress_count > poll_suppress_count)
+ abort ();
+ while (catch->poll_suppress_count < poll_suppress_count)
+ start_polling ();
+
do
{
last_time = catchlist == catch;
+
+ /* Unwind the specpdl stack, and then restore the proper set of
+ handlers. */
unbind_to (catchlist->pdlcount, Qnil);
handlerlist = catchlist->handlerlist;
catchlist = catchlist->next;
gcprolist = catch->gcpro;
backtrace_list = catch->backlist;
lisp_eval_depth = catch->lisp_eval_depth;
+
+ _longjmp (catch->jmp, 1);
}
DEFUN ("throw", Fthrow, Sthrow, 2, 2, 0,
for (c = catchlist; c; c = c->next)
{
if (EQ (c->tag, tag))
- {
- /* Restore the polling-suppression count. */
- if (c->poll_suppress_count > poll_suppress_count)
- abort ();
- while (c->poll_suppress_count < poll_suppress_count)
- start_polling ();
- c->val = val;
- unbind_catch (c);
- _longjmp (c->jmp, 1);
- }
+ unwind_to_catch (c, val);
}
tag = Fsignal (Qno_catch, Fcons (tag, Fcons (val, Qnil)));
}
Lisp_Object val;
struct catchtag c;
struct handler h;
- register Lisp_Object tem;
+ register Lisp_Object var, bodyform, handlers;
- tem = Fcar (args);
- CHECK_SYMBOL (tem, 0);
+ var = Fcar (args);
+ bodyform = Fcar (Fcdr (args));
+ handlers = Fcdr (Fcdr (args));
+ CHECK_SYMBOL (var, 0);
+
+ for (val = handlers; ! NILP (val); val = Fcdr (val))
+ {
+ Lisp_Object tem;
+ tem = Fcar (val);
+ if ((!NILP (tem)) &&
+ (!CONSP (tem) || (XTYPE (XCONS (tem)->car) != Lisp_Symbol)))
+ error ("Invalid condition handler", tem);
+ }
c.tag = Qnil;
c.val = Qnil;
if (!NILP (h.var))
specbind (h.var, Fcdr (c.val));
val = Fprogn (Fcdr (Fcar (c.val)));
+
+ /* Note that this just undoes the binding of h.var; whoever
+ longjumped to us unwound the stack to c.pdlcount before
+ throwing. */
unbind_to (c.pdlcount, Qnil);
return val;
}
c.next = catchlist;
catchlist = &c;
- h.var = Fcar (args);
- h.handler = Fcdr (Fcdr (args));
-
- for (val = h.handler; ! NILP (val); val = Fcdr (val))
- {
- tem = Fcar (val);
- if ((!NILP (tem)) &&
- (!CONSP (tem) || (XTYPE (XCONS (tem)->car) != Lisp_Symbol)))
- error ("Invalid condition handler", tem);
- }
+ h.var = var;
+ h.handler = handlers;
h.next = handlerlist;
- h.poll_suppress_count = poll_suppress_count;
h.tag = &c;
handlerlist = &h;
- val = Feval (Fcar (Fcdr (args)));
+ val = Feval (bodyform);
catchlist = c.next;
handlerlist = h.next;
return val;
catchlist = &c;
h.handler = handlers;
h.var = Qnil;
- h.poll_suppress_count = poll_suppress_count;
h.next = handlerlist;
h.tag = &c;
handlerlist = &h;
return debugger_value;
#else
if (EQ (clause, Qlambda))
+ {
+ /* We can't return values to code which signalled an error, but we
+ can continue code which has signalled a quit. */
+ if (EQ (sig, Qquit))
+ return Qnil;
+ else
error ("Returning a value from an error is no longer supported");
+ }
#endif
if (!NILP (clause))
{
struct handler *h = handlerlist;
- /* Restore the polling-suppression count. */
- if (h->poll_suppress_count > poll_suppress_count)
- abort ();
- while (h->poll_suppress_count < poll_suppress_count)
- start_polling ();
handlerlist = allhandlers;
- unbind_catch (h->tag);
- h->tag->val = Fcons (clause, Fcons (sig, data));
- _longjmp (h->tag->jmp, 1);
+ unwind_to_catch (h->tag, Fcons (clause, Fcons (sig, data)));
}
}
{
if (wants_debugger (Vstack_trace_on_error, conditions))
internal_with_output_to_temp_buffer ("*Backtrace*", Fbacktrace, Qnil);
- if (!entering_debugger
- && (EQ (sig, Qquit) ? debug_on_quit
- : wants_debugger (Vdebug_on_error, conditions)))
+ if ((EQ (sig, Qquit)
+ ? debug_on_quit
+ : wants_debugger (Vdebug_on_error, conditions))
+ && when_entered_debugger < num_nonmacro_input_chars)
{
int count = specpdl_ptr - specpdl;
specbind (Qdebug_on_error, Qnil);
max_specpdl_size = 400;
if (specpdl_size >= max_specpdl_size)
{
+ if (!NILP (Vdebug_on_error))
+ /* Leave room for some specpdl in the debugger. */
+ max_specpdl_size = specpdl_size + 100;
Fsignal (Qerror,
Fcons (build_string ("Variable binding depth exceeds max-specpdl-size"), Qnil));
- max_specpdl_size *= 2;
}
}
specpdl_size *= 2;
extern Lisp_Object Vprint_level;
struct gcpro gcpro1;
- entering_debugger = 0;
-
XFASTINT (Vprint_level) = 3;
tail = Qnil;