[Tcl-bugs] [ tcl-Patches-2868499 ] TIP #348: Substituted errorStack

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Patches item #2868499, was opened at 2009-09-28 01:57
Message generated for change (Comment added) made by ferrieux
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Category: None
Group: TIP Implementation
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Alexandre Ferrieux (ferrieux)
Assigned to: miguel sofer (msofer)
Summary: TIP #348: Substituted errorStack

Initial Comment:
Here is a crude but functional implementation of TIP #348.
The variable ::errorStack, comes to life when defined (which is not the case by default, to avoid any performance hit).
While unwinding, it is populated by substituted argslists as described in the TIP.
It is automatically reset (to the empty list)  whenever ::errorInfo is. (But this leaves it enabled. To disable it, unset it.)

(Among crudities: uses ::errorStack instead of ::tcl::errorStack, doesn't pay attention to code style, no test cases.
Also, it inserts two fields in the private interp structure, right in the middle, not at the end. ABI hazard, don't forget to 'make clean' after applying  ;-)



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>Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-10-31 17:37

Message:
Test suite now fixed. Thanks to -match glob :)

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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-10-31 17:01

Message:
Patch now restricted as per Joe's recommendations on tclcore:
 - always on
 - non-flat list
 - with options dict
Test suite now needs fixes wherever the options dict was checked in
extenso...

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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-10-23 03:03

Message:
Extended patch adds bit value 4 as "flat list", ie errorstack is built as
 2 foo bar 1 baz 2 gnu gnats
instead of
 {foo bar} baz {gnu gnats}
Hence:
   use=0 : pristine
   use=1 : info errorstack
   use=2 : + dict
   use=5 : 1 + flatlist
   use=6 : 2 + flatlist

Timings below:
Case: Ten-fold catch ladder use=0 -> 101.3854 microseconds per iteration
Case: Ten-fold catch ladder use=1 -> 106.2653 microseconds per iteration
Case: Ten-fold catch ladder use=2 -> 106.8439 microseconds per iteration
Case: Ten-fold catch ladder use=5 -> 103.5229 microseconds per iteration
Case: Ten-fold catch ladder use=6 -> 103.7669 microseconds per iteration
Case: Single Catch with opt dict use=0 -> 25.814 microseconds per
iteration
Case: Single Catch with opt dict use=1 -> 26.2905 microseconds per
iteration
Case: Single Catch with opt dict use=2 -> 27.0002 microseconds per
iteration
Case: Single Catch with opt dict use=5 -> 26.0665 microseconds per
iteration
Case: Single Catch with opt dict use=6 -> 26.783 microseconds per
iteration

Conclusion: while the gain for a tight catch loop is negligible, for a
ten-fold  catch ladder building a long errorstack it is substantial: the
flatlist roughly divides the overhead by three.

However, the flatlist is a bit less convenient for the programmer.
It could be postprocessed into a nested list in [info errorstack] but not
int the options dict...


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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-10-20 18:17

Message:
Attaching a new patch, errorstack2.patch, fulfilling Joe's request of [info
errostack ?interp?] and [dict get $d -errostack].
I left the ::tcl::useErrorStack control variable for perf measurements:
    0 --> pristine HEAD
    1 --> just [info errorstack]
    2 ---> adds options dict entry -errorstack

Note the implementation still uses ckalloc-based Tcl_NewListObj for
argslist, pending proof that optimization is needed.
Here are the figures:

Case: Ten-fold catch ladder  use=0 ->    74.7924 microseconds per
iteration
Case: Ten-fold catch ladder  use=1 ->    76.7888 microseconds per
iteration
Case: Ten-fold catch ladder  use=2 ->    77.1977 microseconds per
iteration
Case: Single Catch with opt dict  use=0 ->    19.2613 microseconds per
iteration
Case: Single Catch with opt dict  use=1 ->    19.7608 microseconds per
iteration
Case: Single Catch with opt dict  use=2 ->    20.2815 microseconds per
iteration

with code:

for {set i 1} {$i<10} {incr i} {
	proc f$i x "f[expr {$i+1}] \$x"
}
proc f10 x {error F10:$x}

proc boo {} {error BOO}

proc catchloop {} {
	for {set i 0} {$i<100000} {incr i} {
		if {[catch boo m d]} continue
	}
}

foreach {mm ss} {
	"Ten-fold catch ladder" {catch {f1 12}}
	"Single Catch with opt dict" {catch boo m d}
} {
	
	foreach v {0 1 2} {
		set ::tcl::useErrorStack $v
		puts "Case: $mm  use=$v ->    [time $ss 10000]"
	}
}

       

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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-10-05 10:12

Message:
Complete with test cases now.

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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-10-05 02:46

Message:
Mostly done.
- now the var is ::tcl::errorStack and the flag is ::tcl::useErrorStack
- zero overhead when ::tcl::useErrorStack is 0 (default)
- uses a read trace to postpone var machinery until real use
- uses an optimized in-place lappend/reset to keep the list intrep as much
as possible (just as fast as the linked list approach IMO)
TBD: test cases.

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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2009-09-29 01:00

Message:
First slight improvement: explicitly skip iPtr->rootFramePtr, like in [info
level $n], since the root frame will always have argc==0. This removes the
parasitic {} always found at the end of ::errorStack, and also an extra one
generated by [tailcall] and [coroutine].

Next improvements planned:

(1) make the on/off switch more efficient by using a linked boolean var
rather than the existence of ::errorStack which costs a hash lookup when
negative.

(2) make the list building slightly more efficient by using a backbone of
Tcl_Obj as Cons'es (linked list), and turning it into a Tcl list only in a
read trace attached to ::errorStack (instead of directly lappending as is
currently the case. This construction is wasted in caught, expected
exception handling where the errorStack is not used).

(3) proper ::tcl namespace + test cases.


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