Exception mechanism internals - Revision history

Manus at 12:17, 21 January 2016

2016-01-21T12:17:52Z

Manus at 12:15, 21 January 2016

2016-01-21T12:15:55Z

Ted at 07:10, 26 June 2012

2012-06-26T07:10:55Z

Ted: New page: Category:Exception == Overview == This article documents exception handling mechanisms at implementation level, including runtime and code generation. == Typical execution/trace stack...

2012-06-26T07:01:14Z

New page: Category:Exception == Overview == This article documents exception handling mechanisms at implementation level, including runtime and code generation. == Typical execution/trace stack...

New page

[[Category:Exception]]
== Overview ==
This article documents exception handling mechanisms at implementation level, including runtime and code generation.

== Typical execution/trace stack operation in a routine ==
Once or routine with old variable is slightly different.
See following pseudocode:

<eiffel>
-- entry

new_exset
do
-- eif_stack: Create a new vector EX_CALL on eif_stack.
end

if not setjmp then

-- Routine body

else

exresc

do

-- eif_trace: Check the stack of eif_trace top element must be EN_FAIL or EN_RES

-- eif_trace: Mark top node as rescued

-- eif_trace: Create new EN_ILVL item on eif_trace, indicating entering a new level

-- eif_stack: Create new EX_RESC vector on eif_stack.

end

Rescue_body

-- If there is retry clause, it calls

exret

do

-- eif_stack: Check top vector of eif_stack is EX_RESC

-- eif_stack: Override top item of eif_stack with the vector of current routine (saved as local). Change the type of the vector to EX_RETY

-- eif_trace: Pop off eif_trace, which must be EN_ILVL item

-- eif_trace: unwind_trace, pop items from eif_trace until EN_ILVL item is found. Restore `exdata' at previous level.

end

-- If no retry is called, call at the end:

exfail

do

-- eif_stack: pop EX_RESC from eif_stack

-- eif_trace: pop EN_ILVL from eif_trace, leaving call failures created by `draise' on stack.

-- create last_exception (ROUTINE_FAILURE)

-- eif_stack: call `backtrack' which will pop eif_stack until find the top most jmpbuf.

-- Call longjmp with the found jmpbuf.

end

end

exok

do

-- eif_stack: Pop eif_stack until a EX_CALL, EX_RESC, EX_RETY or EX_OSTK is found and popped.

-- eif_trace: unwind_trace, pop item from eif_trace until we find EN_ILVL item. Restore `exdata' at previous level.

end
</eiffel>

@@ Line 1: / Line 1: @@
 [[Category:Exception]]
 [[Category:Code Generation]]
-[[Category:Language]]
+[[Category:Eiffel Language]]
 == Overview ==

← Older revision		Revision as of 07:10, 26 June 2012
Line 84:		Line 84:
	end		end
	</eiffel>		</eiffel>
		+
		+	== Raise an exception (draise, eraise, com_raise, ) ==
		+
		+	* Create a new item on eif_trace, with the type the exception.
		+
		+	* Pop and push back eif_stack in order to get information. Fill those information into `exdata'.
		+
		+	* Setup information for top node in eif_trace.
		+
		+	* In make_exception, when building trace, traverse eif_stack, and push corresponding items into eif_trace, until jmp pointer is found. In the meantime, if the item is EX_RESC, we change it to EN_OLVL and put into eif_trace.
		+
		+	* Continue buidling trace from the rest element of eif_stack until root node is reached.
		+
		+	* Call `back_track' to really pop off items in eif_stack and call longjmp when the first jmp pointer is found.
		+
		+	== System signal handler ==
		+
		+	* Push an EN_ILVL item on eif_trace
		+
		+	* Push an EX_HDLR item on eif_stack and setup a jmpbuf
		+
		+	* Call exception handler and be ready to longjmp back and call eraise to populate the exception.