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Posted to dev@turbine.apache.org by Christian Asmussen <kr...@kriconet.com.br> on 2002/02/16 20:05:36 UTC
Recursion -> Possible infinite loop
I got across a problem, and would like to know if you guys have a formal
way of dealing with it. Supose we have the following recursive method
public int getDepth(){
return getParent() == null ? 0 : getParent().getDepth() + 1;
}
If an interface disigner creates an object with "setParent(this)" then
getDepth would cause an infinite loop. Depending on the method, this
could cause a whole server to go OOME. Whats the best for to deal whit
this? I thought of three ways of avoiding it. What's the best one?
1 - Simply avoid recursion
2 - Something like semaphores
boolean recursing = false;
public int getDepth(){
if(recursing) throw new RuntimeException("DeadLock");
recursing = true;
int ret = 0;
if(getParent() != null)
ret = 1 + getParent().getDepth();
recursing = false;
return ret;
}
3 - Keep some kinda graph (vertices are conected by getDepth()), something
like:
public void setParent(ThisObject o){
if(formsCycle(o)) throw new Exception("Cycle detected");
...
}
Maybe I should have sent this message to the user list? If so, sorry.
Tks
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we would literally astound ourselves"
- Thomas Edison
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Re: Recursion -> Possible infinite loop
Posted by Daniel Rall <dl...@finemaltcoding.com>.
Christian Asmussen <kr...@kriconet.com.br> writes:
> On 16 Feb 2002, Jason van Zyl wrote:
>
>> On Sat, 2002-02-16 at 14:05, Christian Asmussen wrote:
>> > I got across a problem, and would like to know if you guys have a formal
>> > way of dealing with it. Supose we have the following recursive method
>> >
>> > public int getDepth(){
>> > return getParent() == null ? 0 : getParent().getDepth() + 1;
>> > }
>> >
>> >
>> > If an interface disigner creates an object with "setParent(this)" then
>> > getDepth would cause an infinite loop. Depending on the method, this
>> > could cause a whole server to go OOME. Whats the best for to deal whit
>> > this? I thought of three ways of avoiding it. What's the best one?
>>
>> If in this particular case you required an acyclic graph of objects then
>> you could either use something like a class invariant or an assertion to
>> make sure that the parameter to setParent(Object o) isn't itself.
>
> But what if the guy goes getParent().setParent(this); or more? Ooops you
> sayd acyclic right ;-) But I assume it is the developers task to avoid
> this right?
An IllegalArgumentException or subclass could be thrown. Submit a
patch:
http://jakarta.apache.org/site/source.html
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Re: Recursion -> Possible infinite loop
Posted by Christian Asmussen <kr...@kriconet.com.br>.
On 16 Feb 2002, Jason van Zyl wrote:
> On Sat, 2002-02-16 at 14:05, Christian Asmussen wrote:
> > I got across a problem, and would like to know if you guys have a formal
> > way of dealing with it. Supose we have the following recursive method
> >
> > public int getDepth(){
> > return getParent() == null ? 0 : getParent().getDepth() + 1;
> > }
> >
> >
> > If an interface disigner creates an object with "setParent(this)" then
> > getDepth would cause an infinite loop. Depending on the method, this
> > could cause a whole server to go OOME. Whats the best for to deal whit
> > this? I thought of three ways of avoiding it. What's the best one?
>
> If in this particular case you required an acyclic graph of objects then
> you could either use something like a class invariant or an assertion to
> make sure that the parameter to setParent(Object o) isn't itself.
But what if the guy goes getParent().setParent(this); or more? Ooops you
sayd acyclic right ;-) But I assume it is the developers task to avoid
this right?
--
"If we did all the things we are capable of,
we would literally astound ourselves"
- Thomas Edison
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Re: Recursion -> Possible infinite loop
Posted by Jason van Zyl <jv...@zenplex.com>.
On Sat, 2002-02-16 at 14:05, Christian Asmussen wrote:
> I got across a problem, and would like to know if you guys have a formal
> way of dealing with it. Supose we have the following recursive method
>
> public int getDepth(){
> return getParent() == null ? 0 : getParent().getDepth() + 1;
> }
>
>
> If an interface disigner creates an object with "setParent(this)" then
> getDepth would cause an infinite loop. Depending on the method, this
> could cause a whole server to go OOME. Whats the best for to deal whit
> this? I thought of three ways of avoiding it. What's the best one?
If in this particular case you required an acyclic graph of objects then
you could either use something like a class invariant or an assertion to
make sure that the parameter to setParent(Object o) isn't itself.
--
jvz.
Jason van Zyl
jvanzyl@apache.org
http://tambora.zenplex.org
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