Hi Terry (and David),

I was wondering if there are any news 
on the floundering issue. 

In the meanwhile I have what appears to be another 
bug to report. I am using the basic loop structure 
that's shown in the manual to get answers to a query: 

int rc = xsb_query_string_string(query_thread, goal,&return_string,"|"); 
while (rc == XSB_SUCCESS) {
   char* answer = return_string.string;
   // do stuff with answer ...
   rc = xsb_next_string(query_thread, &return_string,"|");
   if (rc == XSB_ERROR) 
     ... print some error message ... 

The loop starts out fine, processes a few answers, but then 
on some iteration and for some reason I don't understand, the 
call to xsb_next_string crashes the system with the error message: 
"Partial forward continuation." The query is well-formed, 
so I don't quite understand the crash. It seems that the loop 
should conclude with the remaining answers, if any. At any rate, 
even if the call to xsb_next_string causes an error on the
n^th iteration, shouldn't that be captured in the value of
rc and handled by the next line, if (rc == XSB_ERROR)? 
That's question #1.

Question #2: After digging around a bit, it appears that
the call to xsb_next_string inside the while loop crashes 
when it's time to resolve a rule whose body involves 
both static and dynamic predicates. Before that point, 
all of the rules considered involved only dynamic predicates. 
But the minute a mixed-body rule is examined, xsb_next_string 
breaks. Is that a coincidence or is it meaningful? 

Unsurprisingly btw, this is not reproducible in pure XSB.
When I spawn a thread to do the same query in the command-line
interface, I get the right answers without an error. 

As usual, any feedback will be highly appreciated.


On Aug 22, 2012, at 10:25 AM, Terrance Swift <tswift@cs.stonybrook.edu> wrote:

Yes, that is an odd error.  I'll take a look ASAP -- today is pretty booked, but I should have time this evening or tomorrow morning.


From: K. A. [k_a_7245@yahoo.com]
Sent: Tuesday, August 21, 2012 4:56 PM
To: David Warren
Cc: Xsb-development@lists.sourceforge.net; Terrance Swift
Subject: Re: Bug in multi-threaded XSB?

Hi David, Terry,

The manual lists abolish_all_private_tables/0 (in Chapter 6)
as a "standard predicate", described on p. 100 as predicates 
"which are always available to the Prolog interpreter and do 
not need to be imported or loaded explicitly as do other Prolog 
predicates." Terry has volunteered to fix that in the manual

I've run into what appears to be a threading bug though, which
I hope that Terry can shed some light on. Per Terry's suggestion,
I've declared privately tabled versions of all my shared dynamic 
predicates, by appending the capital letter 'P' at the end of 
each predicate's name (e.g., if I have a shared dynamic predicate 
'before' then I introduce a privately tabled predicate 'beforeP'). 
Then I define the privately tabled versions to be supersets of the shared ones (again, as Terry suggested), e.g.:

beforeP(X,Y,Z) :- before(X,Y,Z).

However, I'm running into another thread issue, which is 
(again) a discepancy between doing something on the main
thread and doing the exact same thing on a spawned thread.
This time I was able to reproduce the problem in pure 
XSB - no C involved. Consider the following interaction
with XSB:

findall(X/Y/L,familyOfP(X,Y,L),R), write(R). 

(See below for the contents of prelude.P.)

This works fine (because it's done on the main thread): 
it correctly reasons out that a is familyOfP b, b is familyOfP a, 
etc. Now I *should* get the same result when I evaluate 
this query on a spawned thread. But I don't. When I do:

thread_create((findall(X/Y/L,familyOfP(X,Y,L),R),Id), thread_join(Id,ExitCode).

I get the following odd error:

| ?- thread_create((findall(X/Y/L,familyOfP(X,Y,L),R),write(R)),Id), thread_join(Id,ExitCode).
++Error[XSB/Runtime/P]: [Miscellaneous] [th 1]  Floundering goal in tnot/1 familyOfP(_v185356496

X = _h171
Y = _h185
L = _h199
R = _h261
Id = 1

ExitCode = exception(error(misc_error,[th 1]  Floundering goal 
in tnot/1 familyOfP(_v185356496,[[Forward Continuation...,... 
standard:call/1,... standard:call_c/1,... standard:call/1,... 
standard:call/1],Backward Continuation...]))

This is especially perplexing given that there is no negation
anywhere, tabled or otherwise. How/where does floundering enter 
the picture? I've actually run into a number of such "floundering" 
errors recently while trying to do seemingly innocuous things on 
spawned threads. (I've forwarded some such errors before to David, 
though we were both stumped by the nature of the error message.) 
Again, I've only seen such errors on spawned threads, never on 
the main XSB thread. Clarification/feedback would be appreciated.


The contents of prelude.P are pasted below. Most of this stuff
is irrelevant to the problem, but I've spent the last 3 hours
throwing away the majority of the stuff from prelude.P. What's left
is, I think, pretty manageable and readable:

:- import append/3 from basics.

appendAll([H|T],L) :- appendAll(T,L1), append(H,L1,L).

append3(L1,L2,L3,L) :- append(L1,L2,R), append(L3,R,L).
append4(L1,L2,L3,L4,L) :- append3(L1,L2,L3,R), append(L4,R,L).
append5(L1,L2,L3,L4,L5,L) :- append4(L1,L2,L3,L4,R), append(L5,R,L).

            Private tabled predicate declarations 

:- table afterP/3 as private.
:- table beforeP/3 as private.
:- table dateAfterP/3 as private.
:- table dateBeforeP/3 as private.
:- table intervalAfterP/3 as private.
:- table intervalBeforeP/3 as private.
:- table differentFromP/3 as private.
:- table knowsOfP/3 as private.
:- table relatedPersonOfP/3 as private.
:- table familyOfP/3 as private.
:- table auntOfP/3 as private.
:- table cousinOfP/3 as private.
:- table nephewOfP/3 as private.
:- table nieceOfP/3 as private.
:- table uncleOfP/3 as private.
:- table ancestorOfP/3 as private.
:- table grandParentOfP/3 as private.
:- table grandMotherOfP/3 as private.
:- table grandFatherOfP/3 as private.
:- table parentOfP/3 as private.
:- table fatherOfP/3 as private.
:- table motherOfP/3 as private.
:- table descendantOfP/3 as private.
:- table childOfP/3 as private.
:- table daughterOfP/3 as private.
:- table sonOfP/3 as private.
:- table grandChildOfP/3 as private.
:- table grandsonOfP/3 as private.
:- table granddaughterOfP/3 as private.
:- table inLawOfP/3 as private.
:- table brotherInLawOfP/3 as private.
:- table daughterInLawOfP/3 as private.
:- table fatherInLawOfP/3 as private.
:- table motherInLawOfP/3 as private.
:- table sisterInLawOfP/3 as private.
:- table sonInLawOfP/3 as private.
:- table siblingOfP/3 as private.
:- table brotherOfP/3 as private.
:- table sisterOfP/3 as private.
:- table spouseOfP/3 as private.
:- table husbandOfP/3 as private.
:- table wifeOfP/3 as private.
:- table unknownPersonRelationP/3 as private.
:- table endsInDateP/3 as private.
:- table startsInDateP/3 as private.
:- table expirationDateP/3 as private.
:- table hasLocationP/3 as private.
:- table ownedByP/3 as private.
:- table involvedP/3 as private.
:- table occursInP/3 as private.
:- table occursDuringP/3 as private.
:- table operationAreaP/3 as private.
:- table ownerOfP/3 as private.
:- table relatedEventP/3 as private.
:- table teacherP/3 as private.
:- table relationObjectP/3 as private.
:- table studentP/3 as private.
:- table ageP/3 as private.
:- table dateDayP/3 as private.
:- table dateMonthP/3 as private.
:- table dateYearP/3 as private.
:- table descriptionP/3 as private.
:- table dateP/1 as private.
:- table dateIntervalP/1 as private.
:- table eventP/1 as private.
:- table locationP/1 as private.
:- table cityP/1 as private.
:- table countryP/1 as private.
:- table regionP/1 as private.
:- table stateP/1 as private.

            Dynamic predicate declarations 

:- dynamic after/3 as shared.
:- dynamic before/3 as shared.
:- dynamic dateAfter/3 as shared.
:- dynamic dateBefore/3 as shared.
:- dynamic intervalAfter/3 as shared.
:- dynamic intervalBefore/3 as shared.
:- dynamic differentFrom/3 as shared.
:- dynamic knowsOf/3 as shared.
:- dynamic relatedPersonOf/3 as shared.
:- dynamic familyOf/3 as shared.
:- dynamic auntOf/3 as shared.
:- dynamic cousinOf/3 as shared.
:- dynamic nephewOf/3 as shared.
:- dynamic nieceOf/3 as shared.
:- dynamic uncleOf/3 as shared.
:- dynamic ancestorOf/3 as shared.
:- dynamic grandParentOf/3 as shared.
:- dynamic grandMotherOf/3 as shared.
:- dynamic grandFatherOf/3 as shared.
:- dynamic parentOf/3 as shared.
:- dynamic fatherOf/3 as shared.
:- dynamic motherOf/3 as shared.
:- dynamic descendantOf/3 as shared.
:- dynamic childOf/3 as shared.
:- dynamic daughterOf/3 as shared.
:- dynamic sonOf/3 as shared.
:- dynamic grandChildOf/3 as shared.
:- dynamic grandsonOf/3 as shared.
:- dynamic granddaughterOf/3 as shared.
:- dynamic inLawOf/3 as shared.
:- dynamic brotherInLawOf/3 as shared.
:- dynamic daughterInLawOf/3 as shared.
:- dynamic fatherInLawOf/3 as shared.
:- dynamic motherInLawOf/3 as shared.
:- dynamic sisterInLawOf/3 as shared.
:- dynamic sonInLawOf/3 as shared.
:- dynamic siblingOf/3 as shared.
:- dynamic brotherOf/3 as shared.
:- dynamic sisterOf/3 as shared.
:- dynamic spouseOf/3 as shared.
:- dynamic husbandOf/3 as shared.
:- dynamic wifeOf/3 as shared.
:- dynamic unknownPersonRelation/3 as shared.
:- dynamic endsInDate/3 as shared.
:- dynamic startsInDate/3 as shared.
:- dynamic expirationDate/3 as shared.
:- dynamic hasLocation/3 as shared.
:- dynamic ownedBy/3 as shared.
:- dynamic involved/3 as shared.
:- dynamic occursIn/3 as shared.
:- dynamic occursDuring/3 as shared.
:- dynamic operationArea/3 as shared.
:- dynamic ownerOf/3 as shared.
:- dynamic relatedEvent/3 as shared.
:- dynamic teacher/3 as shared.
:- dynamic relationObject/3 as shared.
:- dynamic student/3 as shared.
:- dynamic age/3 as shared.
:- dynamic dateDay/3 as shared.
:- dynamic dateMonth/3 as shared.
:- dynamic dateYear/3 as shared.
:- dynamic description/3 as shared.
:- dynamic date/1 as shared.
:- dynamic dateInterval/1 as shared.
:- dynamic event/1 as shared.
:- dynamic location/1 as shared.
:- dynamic city/1 as shared.
:- dynamic country/1 as shared.
:- dynamic region/1 as shared.
:- dynamic state/1 as shared.


            Private predicate definitions

afterP(X,Y,L) :- after(X,Y,L).
beforeP(X,Y,L) :- before(X,Y,L).
dateAfterP(X,Y,L) :- dateAfter(X,Y,L).
dateBeforeP(X,Y,L) :- dateBefore(X,Y,L).
intervalAfterP(X,Y,L) :- intervalAfter(X,Y,L).
intervalBeforeP(X,Y,L) :- intervalBefore(X,Y,L).
differentFromP(X,Y,L) :- differentFrom(X,Y,L).
knowsOfP(X,Y,L) :- knowsOf(X,Y,L).
relatedPersonOfP(X,Y,L) :- relatedPersonOf(X,Y,L).
familyOfP(X,Y,L) :- familyOf(X,Y,L).
auntOfP(X,Y,L) :- auntOf(X,Y,L).
cousinOfP(X,Y,L) :- cousinOf(X,Y,L).
nephewOfP(X,Y,L) :- nephewOf(X,Y,L).
nieceOfP(X,Y,L) :- nieceOf(X,Y,L).
uncleOfP(X,Y,L) :- uncleOf(X,Y,L).
ancestorOfP(X,Y,L) :- ancestorOf(X,Y,L).
grandParentOfP(X,Y,L) :- grandParentOf(X,Y,L).
grandMotherOfP(X,Y,L) :- grandMotherOf(X,Y,L).
grandFatherOfP(X,Y,L) :- grandFatherOf(X,Y,L).
parentOfP(X,Y,L) :- parentOf(X,Y,L).
fatherOfP(X,Y,L) :- fatherOf(X,Y,L).
motherOfP(X,Y,L) :- motherOf(X,Y,L).
descendantOfP(X,Y,L) :- descendantOf(X,Y,L).
childOfP(X,Y,L) :- childOf(X,Y,L).
daughterOfP(X,Y,L) :- daughterOf(X,Y,L).
sonOfP(X,Y,L) :- sonOf(X,Y,L).
grandChildOfP(X,Y,L) :- grandChildOf(X,Y,L).
grandsonOfP(X,Y,L) :- grandsonOf(X,Y,L).
granddaughterOfP(X,Y,L) :- granddaughterOf(X,Y,L).
inLawOfP(X,Y,L) :- inLawOf(X,Y,L).
brotherInLawOfP(X,Y,L) :- brotherInLawOf(X,Y,L).
daughterInLawOfP(X,Y,L) :- daughterInLawOf(X,Y,L).
fatherInLawOfP(X,Y,L) :- fatherInLawOf(X,Y,L).
motherInLawOfP(X,Y,L) :- motherInLawOf(X,Y,L).
sisterInLawOfP(X,Y,L) :- sisterInLawOf(X,Y,L).
sonInLawOfP(X,Y,L) :- sonInLawOf(X,Y,L).
siblingOfP(X,Y,L) :- siblingOf(X,Y,L).
brotherOfP(X,Y,L) :- brotherOf(X,Y,L).
sisterOfP(X,Y,L) :- sisterOf(X,Y,L).
spouseOfP(X,Y,L) :- spouseOf(X,Y,L).
husbandOfP(X,Y,L) :- husbandOf(X,Y,L).
wifeOfP(X,Y,L) :- wifeOf(X,Y,L).
unknownPersonRelationP(X,Y,L) :- unknownPersonRelation(X,Y,L).
endsInDateP(X,Y,L) :- endsInDate(X,Y,L).
startsInDateP(X,Y,L) :- startsInDate(X,Y,L).
expirationDateP(X,Y,L) :- expirationDate(X,Y,L).
hasLocationP(X,Y,L) :- hasLocation(X,Y,L).
ownedByP(X,Y,L) :- ownedBy(X,Y,L).
involvedP(X,Y,L) :- involved(X,Y,L).
occursInP(X,Y,L) :- occursIn(X,Y,L).
occursDuringP(X,Y,L) :- occursDuring(X,Y,L).
operationAreaP(X,Y,L) :- operationArea(X,Y,L).
ownerOfP(X,Y,L) :- ownerOf(X,Y,L).
relatedEventP(X,Y,L) :- relatedEvent(X,Y,L).
teacherP(X,Y,L) :- teacher(X,Y,L).
relationObjectP(X,Y,L) :- relationObject(X,Y,L).
studentP(X,Y,L) :- student(X,Y,L).
ageP(X,Y,L) :- age(X,Y,L).
dateDayP(X,Y,L) :- dateDay(X,Y,L).
dateMonthP(X,Y,L) :- dateMonth(X,Y,L).
dateYearP(X,Y,L) :- dateYear(X,Y,L).
descriptionP(X,Y,L) :- description(X,Y,L).
dateP(X) :- date(X).
dateIntervalP(X) :- dateInterval(X).
eventP(X) :- event(X).
locationP(X) :- location(X).
cityP(X) :- city(X).
countryP(X) :- country(X).
regionP(X) :- region(X).
stateP(X) :- state(X).
schoolP(X) :- school(X).
personP(X) :- person(X).
relationP(X) :- relation(X).
directRelationP(X) :- directRelation(X).
acquaintanceP(X) :- acquaintance(X).
cohabitationP(X) :- cohabitation(X).
colleagueshipP(X) :- colleagueship(X).
enmityP(X) :- enmity(X).
friendshipP(X) :- friendship(X).
neighborhoodP(X) :- neighborhood(X).
teachingP(X) :- teaching(X).
indirectRelationP(X) :- indirectRelation(X).

            Subproperty rules 

relationObjectP(X,Y,L) :- studentP(X,Y,L).
relationSubjectP(X,Y,L) :- teacherP(X,Y,L).
differentFromP(X,Y,L) :- knowsOfP(X,Y,L).
knowsOfP(X,Y,L) :- relatedPersonOfP(X,Y,L).
relatedPersonOfP(X,Y,L) :- unknownPersonRelationP(X,Y,L).
relatedPersonOfP(X,Y,L) :- familyOfP(X,Y,L).
familyOfP(X,Y,L) :- spouseOfP(X,Y,L).
spouseOfP(X,Y,L) :- wifeOfP(X,Y,L).
spouseOfP(X,Y,L) :- husbandOfP(X,Y,L).
familyOfP(X,Y,L) :- siblingOfP(X,Y,L).
siblingOfP(X,Y,L) :- sisterOfP(X,Y,L).
siblingOfP(X,Y,L) :- brotherOfP(X,Y,L).
familyOfP(X,Y,L) :- inLawOfP(X,Y,L).
inLawOfP(X,Y,L) :- sonInLawOfP(X,Y,L).
inLawOfP(X,Y,L) :- sisterInLawOfP(X,Y,L).
inLawOfP(X,Y,L) :- motherInLawOfP(X,Y,L).
inLawOfP(X,Y,L) :- fatherInLawOfP(X,Y,L).
inLawOfP(X,Y,L) :- daughterInLawOfP(X,Y,L).
inLawOfP(X,Y,L) :- brotherInLawOfP(X,Y,L).
familyOfP(X,Y,L) :- descendantOfP(X,Y,L).
descendantOfP(X,Y,L) :- grandChildOfP(X,Y,L).
grandChildOfP(X,Y,L) :- granddaughterOfP(X,Y,L).
grandChildOfP(X,Y,L) :- grandsonOfP(X,Y,L).
descendantOfP(X,Y,L) :- childOfP(X,Y,L).
childOfP(X,Y,L) :- sonOfP(X,Y,L).
childOfP(X,Y,L) :- daughterOfP(X,Y,L).
familyOfP(X,Y,L) :- ancestorOfP(X,Y,L).
ancestorOfP(X,Y,L) :- parentOfP(X,Y,L).
parentOfP(X,Y,L) :- motherOfP(X,Y,L).
parentOfP(X,Y,L) :- fatherOfP(X,Y,L).
ancestorOfP(X,Y,L) :- grandParentOfP(X,Y,L).
grandParentOfP(X,Y,L) :- grandFatherOfP(X,Y,L).
grandParentOfP(X,Y,L) :- grandMotherOfP(X,Y,L).
familyOfP(X,Y,L) :- uncleOfP(X,Y,L).
familyOfP(X,Y,L) :- nieceOfP(X,Y,L).
familyOfP(X,Y,L) :- nephewOfP(X,Y,L).
familyOfP(X,Y,L) :- cousinOfP(X,Y,L).
familyOfP(X,Y,L) :- auntOfP(X,Y,L).

            Symmetry rules

relatedPersonOfP(X,Y,L) :- relatedPersonOfP(Y,X,L).
intervalOverlapP(X,Y,L) :- intervalOverlapP(Y,X,L).
familyOfP(X,Y,L) :- familyOfP(Y,X,L).
cousinOfP(X,Y,L) :- cousinOfP(Y,X,L).
siblingOfP(X,Y,L) :- siblingOfP(Y,X,L).
spouseOfP(X,Y,L) :- spouseOfP(Y,X,L).

            Transitivity rules

beforeP(X,Y,L) :- beforeP(X,Z,L1), beforeP(Z,Y,L2), append(L1,L2,L).
afterP(X,Y,L) :- afterP(X,Z,L1), afterP(Z,Y,L2), append(L1,L2,L).
dateAfterP(X,Y,L) :- dateAfterP(X,Z,L1), dateAfterP(Z,Y,L2), append(L1,L2,L).
dateBeforeP(X,Y,L) :- dateBeforeP(X,Z,L1), dateBeforeP(Z,Y,L2), append(L1,L2,L).
intervalAfterP(X,Y,L) :- intervalAfterP(X,Z,L1), intervalAfterP(Z,Y,L2), append(L1,L2,L).
intervalBeforeP(X,Y,L) :- intervalBeforeP(X,Z,L1), intervalBeforeP(Z,Y,L2), append(L1,L2,L).
relatedPersonOfP(X,Y,L) :- relatedPersonOfP(X,Z,L1), relatedPersonOfP(Z,Y,L2), append(L1,L2,L).
familyOfP(X,Y,L) :- familyOfP(X,Z,L1), familyOfP(Z,Y,L2), append(L1,L2,L).
ancestorOfP(X,Y,L) :- ancestorOfP(X,Z,L1), ancestorOfP(Z,Y,L2), append(L1,L2,L).
cousinOfP(X,Y,L) :- cousinOfP(X,Z,L1), cousinOfP(Z,Y,L2), append(L1,L2,L).
descendantOfP(X,Y,L) :- descendantOfP(X,Z,L1), descendantOfP(Z,Y,L2), append(L1,L2,L).
siblingOfP(X,Y,L) :- siblingOfP(X,Z,L1), siblingOfP(Z,Y,L2), append(L1,L2,L).
hasLocationP(X,Y,L) :- hasLocationP(X,Z,L1), hasLocationP(Z,Y,L2), append(L1,L2,L).

            Inverse rules

beforeP(X,Y,L) :- afterP(Y,X,L).
afterP(X,Y,L) :- beforeP(Y,X,L).
dateBeforeP(X,Y,L) :- dateAfterP(Y,X,L).
dateAfterP(X,Y,L) :- dateBeforeP(Y,X,L).
intervalBeforeP(X,Y,L) :- intervalAfterP(Y,X,L).
intervalAfterP(X,Y,L) :- intervalBeforeP(Y,X,L).
ancestorOfP(X,Y,L) :- descendantOfP(Y,X,L).
descendantOfP(X,Y,L) :- ancestorOfP(Y,X,L).
childOfP(X,Y,L) :- parentOfP(Y,X,L).
parentOfP(X,Y,L) :- childOfP(Y,X,L).
grandChildOfP(X,Y,L) :- grandParentOfP(Y,X,L).
grandParentOfP(X,Y,L) :- grandChildOfP(Y,X,L).
ownedByP(X,Y,L) :- ownerOfP(Y,X,L).
ownerOfP(X,Y,L) :- ownedByP(Y,X,L).

            Property-Chain rules

uncleOfP(X1,X3,L) :- brotherOfP(X1,X2,L1), parentOfP(X2,X3,L2), append(L1,L2,L).
uncleOfP(X1,X4,L) :- husbandOfP(X1,X2,L1), sisterOfP(X2,X3,L2), parentOfP(X3,X4,L3), append3(L1,L2,L3,L).
parentOfP(X1,X3,L) :- parentOfP(X1,X2,L1), siblingOfP(X2,X3,L2), append(L1,L2,L).
nieceOfP(X1,X3,L) :- daughterOfP(X1,X2,L1), siblingOfP(X2,X3,L2), append(L1,L2,L).
nephewOfP(X1,X3,L) :- sonOfP(X1,X2,L1), siblingOfP(X2,X3,L2), append(L1,L2,L).
sonInLawOfP(X1,X3,L) :- husbandOfP(X1,X2,L1), childOfP(X2,X3,L2), append(L1,L2,L).
sisterInLawOfP(X1,X3,L) :- sisterOfP(X1,X2,L1), spouseOfP(X2,X3,L2), append(L1,L2,L).
sisterInLawOfP(X1,X3,L) :- wifeOfP(X1,X2,L1), siblingOfP(X2,X3,L2), append(L1,L2,L).
motherInLawOfP(X1,X3,L) :- motherOfP(X1,X2,L1), spouseOfP(X2,X3,L2), append(L1,L2,L).
fatherInLawOfP(X1,X3,L) :- fatherOfP(X1,X2,L1), spouseOfP(X2,X3,L2), append(L1,L2,L).
daughterInLawOfP(X1,X3,L) :- wifeOfP(X1,X2,L1), childOfP(X2,X3,L2), append(L1,L2,L).
brotherInLawOfP(X1,X3,L) :- brotherOfP(X1,X2,L1), spouseOfP(X2,X3,L2), append(L1,L2,L).
brotherInLawOfP(X1,X3,L) :- husbandOfP(X1,X2,L1), siblingOfP(X2,X3,L2), append(L1,L2,L).
grandMotherOfP(X1,X3,L) :- motherOfP(X1,X2,L1), parentOfP(X2,X3,L2), append(L1,L2,L).
grandFatherOfP(X1,X3,L) :- fatherOfP(X1,X2,L1), parentOfP(X2,X3,L2), append(L1,L2,L).
grandsonOfP(X1,X3,L) :- sonOfP(X1,X2,L1), childOfP(X2,X3,L2), append(L1,L2,L).
granddaughterOfP(X1,X3,L) :- daughterOfP(X1,X2,L1), childOfP(X2,X3,L2), append(L1,L2,L).

On Aug 21, 2012, at 12:34 PM, David Warren <warren@cs.stonybrook.edu> wrote:

abolish_all_private_tables/0 is defined in thread.P, so I guess you need to import it from there.
The manual should say what module a predicate is defined in, and if it doesn't say it's a standard predicate, then it must be imported


-----Original Message-----
From: K. A. [mailto:k_a_7245@yahoo.com]
Sent: Tuesday, August 21, 2012 10:47 AM
To: Xsb-development@lists.sourceforge.net; David Warren; Terrance Swift
Subject: RE: Bug in multi-threaded XSB?

That's good to hear. After checking with the manual I thought that I would want to call abolish_all_private_tables/0 on a thread poised to answer a query. (This is described on p. 237 of vol. I.) However, when I try that I get:

"Error: [XSB/Runtime/P]: [Existence (No procedure usermod:
abolish_all_private_tables/0 exists)] []"

The command-line version doesn't seem to recognize this predicate either. Do I need to import it first from somewhere?
If that doesn't work, what other alternatives are there for destroying private tables? 



--- On Tue, 8/21/12, Terrance Swift <tswift@cs.stonybrook.edu> wrote:

From: Terrance Swift <tswift@cs.stonybrook.edu>
Subject: RE: Bug in multi-threaded XSB?
To: "K. A." <k_a_7245@yahoo.com>,
<Xsb-development@lists.sourceforge.net>, "David Warren"
Date: Tuesday, August 21, 2012, 8:02 AM Absolutely -- private tables
are handled just as tables in the single threaded engine, so you can
abolish them whenever it makes sense in the single threaded engine. 
Heap gc for threads works just as in the single-threaded engine, and
private dynamic code also works as in the st-engine.


From: K. A. [k_a_7245@yahoo.com]
Sent: Monday, August 20, 2012 10:08 PM
To: Xsb-development@lists.sourceforge.net;
David Warren; Terrance Swift
Subject: RE: Bug in multi-threaded XSB?

Hi Terry,

Thanks for the suggestion. One question: Can a private thread table be
explicitly abolished on that thread while other threads are running?
If so, then your suggestion could work with the unkillable threads
created by xsb_ccall_thread_create - I can maintain a queue of 20 or
so such threads and reuse them to answer queries, since I can't kill
(This would obviously be unworkable in general, but in this case it's
unlikely that I'll have more than 20 concurrent queries at any given
time, so it might be viable.) But this presupposes that I can abolish
their private tables while other threads are running. If not, then I'd
have to continually spawn new threads to answer new queries, and if
these threads never quit then I'll be out of memory before too long.



--- On Mon, 8/20/12, Terrance Swift <tswift@cs.stonybrook.edu>

From: Terrance Swift <tswift@cs.stonybrook.edu>
Subject: RE: Bug in multi-threaded XSB?
To: "K. A." <k_a_7245@yahoo.com>,
"David Warren" <warren@cs.stonybrook.edu>
Date: Monday, August 20, 2012, 9:34 AM Here is the simple attached

A couple of people have written large applications
MT-XSB but they probably did not use all the features
are trying to use, and MT-XSB is certainly less stable
single-threaded XSB.  I wish I had sufficient time
help every user, but looking very briefly at your code,
impossible to understand.

1) Why you can't remove the C/XSB interface, at least
2) Why you can't use thread exiting, at least for
(actually its not an issue from the prolog level,
exit  once they have been joined.)
3) How many of the problems in XSB and how many are
multi-programming errors of yours.  No offense, everybody makes
MT-programming errors.

I hope you'll take seriously the suggestions I gave you
start breaking down the program to help isolate the bugs.  I'll try
to fix the bugs I can once they
clear to me.

From: K. A. [k_a_7245@yahoo.com]
Sent: Sunday, August 19, 2012 7:06 PM
To: Xsb-development@lists.sourceforge.net;
David Warren; Terrance Swift
Subject: RE: Bug in multi-threaded XSB?

Hi Terry,

Thanks for the reply.

You're absolutely right that sharing tables can (and most probably
would) lead to problems with concurrently executing threads.

In principle, it shouldn't.  In local
evaluation, there is a
mechanism to share concurrently evaluated
tables which
I think is described in the manual, and is
in gory
detail in Marques and Swift, 2008 ICLP.

It shouldn't, as long as there are no insertions while concurrent
queries are being answered. But if there are such insertions (as is
almost always the case in question-answering systems), then these
will not occur with abolished tables but
with whatever tables happen to be in effect at
which will in turn depend on the state of the various active queries
at the time. This will most likely invalidate
and lead to wrong results. It seems to me that what
needs is the ability to spawn a query at time t with a
*fresh* (empty)
set of tables and with whatever data happens to be in
database at t. I don't know if, with private predicates/tables,
there is a way to forcibly copy the contents of one thread's
predicates/tables into another. If so, then this could
readily implemented in XSB as things stand. But if
I don't see how XSB's tabling can be used to implement
system that does concurrent updates/queries.

However if you are using MT XSB, I strongly
recommend first
testing out the programming idioms you use from
shell, then putting things into the C-XSB
interface.  XSB's
MT C-Prolog interface is quite ambitious, but
as a
result it
may have some undiagnosed bugs.  Just as
importantly, XSB-only
code will be far, far easier to debug.

I'm sure that's the case, but I would think that the
of having a C<-->XSB interface is to facilitate
for some reason or other, cannot be easily done
in XSB. If I could program the whole thing in XSB by itself, I
could, but I can't. Moreover, it may well be that
are peculiar to the C<-->XSB interface and are
when the code is expressed purely in XSB. What happens

So I tried declaring
tables to be private, *but* it seems you cannot
shared dynamic predicates with private tables. The predicates
themselves (the facts in the database)
to be "dynamic as shared", because otherwise a new
spawned to answer a query would not have any
to work with. But again, the combination "table p/2
with "dynamic p/2 as shared" does not seem to be
by XSB
(perhaps someone can set me straight if I'm

I haven't looked at your code, but in principle
can do this.
See the attached file, though I'm sure that
program is much
more complex than the attached file.

I didn't see an attached file - could you please
I'd be very interested to see how this could be done.

At any rate, we're still left with the more narrow
of why in the world the query threads in this
example are not exiting when they are explicitly

XSB threads should exit when they are killed,
although there are cases ?>>where this doesn't happen.  For instance
if the thread is waiting on
or waiting on a mutex, etc. the waiting thread
to be signaled, to >>wake up, quit doing whatever
doing, and exit.  XSB has a lot of OS
interfaces, and I haven't yet >>handled this in
single case.  In addition, when a thread is
it must clean up after itself, and free what
mutexes, db_cursors, >>etc. that it has (but may
be currently working
on).  While XSB can and does do this for
resources, it doesn't >>always have full
knowledge of
all of the resources a thread has taken.
getting thread cancellation to work in any system is awkward, and
requires a lot from both the
system and
the user.
In pretty much any MT system, its better to
have the
thread itself exit, >>and save thread
cancellation for
special cases.

Well, these are all special cases unfortunately -
*never* exit by themselves because for some reason
which I
quite understand, they go into a read-eval loop
are finished evaluating the goal that they were
to answer. As far as I can see there is no mechanism
the C<-->XSB interface to create a thread to do
job and then quit. The only way to do that would be to execute
embedded XSB code using thread_create, but
keeping track of the thread id and getting the thread to communicate
properly becomes very difficult
again, we are not in XSB proper but in the embedded
world. So xsb_ccall_thread_create seems to be the only viable
option, but again, these threads don't quit by
so killing them is the only option (and an absolute
because it seems that when multiple threads are
tables cannot be abolished, resources cannot be

So if you can show me how your program works from
command-line >interface, I'll help debug at that level.  Once we are
sure the program is >doing
you want at that level, we can see how to add the

Like I said earlier, this seems to assume that the bug will be
reproducible in pure XSB, and I'm not at all sure about that. The C
code sample is very small so I hope someone will be able to take a
look at it and reach a (tentative, at least) verdict. In the
I'll try to take the client/server I've written in C
re-express it in pure XSB using the samples given in
/examples/sockets directory of the distribution. Is
anyone in particular in this list to whom I should
questions pertaining to that client/server code?

Many thanks,


--- On Sat, 8/18/12, David Warren <warren@cs.stonybrook.edu>

From: David Warren <warren@cs.stonybrook.edu>

Subject: RE: Bug in multi-threaded XSB?

To: "K. A." <k_a_7245@yahoo.com>,

Cc: "Terrance Swift" <tswift@cs.stonybrook.edu>

Date: Saturday, August 18, 2012, 12:17 PM

I strongly suspect it is because you

are sharing the tables and that other thread is

(or at least XSB doesn't know it has exited.)

I would suggest that you don't use shared tables

tables. If they are not causing this problem now,

certainly will if you run a multithreaded query

where you have a number of queries and some can

underlying data.


-----Original Message-----

From: K. A. [mailto:k_a_7245@yahoo.com]

Sent: Friday, August 17, 2012 5:24 PM

To: Xsb-development@lists.sourceforge.net

Cc: David Warren; Terrance Swift

Subject: Bug in multi-threaded XSB?

Could someone please explain to me why the
following C

fails to find any answers to the last query in

function - the parentOf(X,Y,L) query?

Note that every insertion does an

and that right before each insertion or query in

should be (as far as I can see) only one XSB
active -

the main one.

I assume this is a bug in multi-threaded XSB

can provide an alternative explanation.

If you put the C code below in a file test.c, you

the program as follows:

gcc -c -I/home/.../XSB/emu


-fno-strict-aliasing -Wall -pipe -D_GNU_SOURCE

gcc -o test.out -lm -ldl -Wl -export-dynamic



#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <string.h>

#include <sys/types.h>

#include <pthread.h>

#include <ctype.h>

#include "cinterf.h"

#include "varstring_xsb.h"

#include "context.h"

void doInsert(char* insertion_command,th_context*

res = xsb_command_string(th,
res =

xsb_command_string(th, insertion_command);}

void doCommand(char* cmd,th_context* th){ int res

xsb_command_string(th, cmd);}

struct QueryArgs {

char* query;

th_context* th;};

void* doQuery(void* args) {

struct QueryArgs * pt = (struct QueryArgs *)

char* query = (*pt).query;

th_context* th = (*pt).th;


th_context* new_query_thread;


int rc =


int answer_count = 0;

while ((rc == XSB_SUCCESS) &&


printf("\nAnswer: %s\n",retstr.string);

rc = xsb_next_string(new_query_thread,



printf("\n%d answers for this query:



return NULL;}

void answerQuery(char* query,th_context* th){

void* exit_status;

pthread_t new_thread;

struct QueryArgs args = {.query = query, .th =





int main() {

char init_string[MAXPATHLEN];

char* xsbHome = getenv("XSB_HOME");

strcpy(init_string, xsbHome);


th_context *main_th = xsb_get_main_thread();








return 0;}

The contents of the other 2 files are as follows:

/************* Contents of prelude.P :


assertAll([H|T]) :- asserta(H),assertAll(T).

/************* Contents of main.P :

:- import append/3 from basics.

:- table motherOf/3 as shared.

:- table fatherOf/3 as shared.

:- table parentOf/3 as shared.

:- table ancestorOf/3 as shared.

:- table auntOf/3 as shared.

:- table familyOf/3 as shared.

:- dynamic motherOf/3 as shared.

:- dynamic fatherOf/3 as shared.

:- dynamic parentOf/3 as shared.

:- dynamic ancestorOf/3 as shared.

:- dynamic auntOf/3 as shared.

:- dynamic familyOf/3 as shared.

familyOf(X,Y,L) :- ancestorOf(X,Y,L).

ancestorOf(X,Y,L) :- parentOf(X,Y,L).

parentOf(X,Y,L) :- motherOf(X,Y,L).

parentOf(X,Y,L) :- fatherOf(X,Y,L).

familyOf(X,Y,L) :- auntOf(X,Y,L).

familyOf(X,Y,L) :- familyOf(Y,X,L).

ancestorOf(X,Y,L) :- ancestorOf(X,Z,L1),