Re: [rules-users] Multiple threading

[Mark Proctor]

On 10/02/2012 22:46, apache wrote:

Mark
  the first link in my previous post says something contradictory to what you
mentioned. I understand that one thread at a time can use the session just
not 2 or more threads at the same time . Is that what you meant too ?
I think you are referring to the javadoc of one particular method, let 
me know if there are others.



 getStatefulKnowledgeSessions

Collection  
<http://download.oracle.com/javase/1.5.0/docs/api/java/util/Collection.html?is-external=true>http://docs.jboss.org/jbpm/v5.2/javadocs/org/drools/runtime/StatefulKnowledgeSession.html>>
  *getStatefulKnowledgeSessions*()

Return a collection of the StatefulKnowledgeSessions that exist in this 
KnowledgeBase. Be careful as sessions are not thread-safe and could be 
in use elsewhere.


That is incorrect and we'll get it corrected for next release.

Mark


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Re: [rules-users] Multiple threading

[Mark Proctor]

On 14/02/2012 02:01, Richard Calmbach wrote:
Sorry to burst your bubble, but stateful knowledge sessions are most 
definitely not thread-safe. I have seen hard evidence to this effect 
in the form of incorrect execution results and log statements that 
clearly show that two threads were interacting in unexpected ways. In 
a nutshell: Rule consequences are not executed atomically. This can 
cause unexpected working memory changes (e.g., fact insertion) to 
happen on one thread in one rule consequence before another thread has 
finished executing another rule consequence. Note that I'm not talking 
about whatever threads Drools may be creating internally. I'm talking 
about application threads.


I have found synchronizing on the session object to be a reliable 
safeguard against unwanted thread interactions. Basically, this way 
all external fact insertions and calls to fireAllRules() are serialized.


If this is not supposed to be necessary (synchronizing on the 
session), then there is a thread-safety bug in Drools.
Over various releases we have tried to catch any areas that might bypass 
these locks. If you have found one, please provide us with a unit test 
and we'll fix.


Mark


-Richard

2012/2/10 Mark Proctor >


On 10/02/2012 03:36, Apache wrote:

Hey,
I am trying to get multiple threads to insert events and run rules against 
the union of events inserted ( an as soon as they are inserted, a timer drools 
thread kicking of fireallrules() is not an option because that would introduce 
a delay ) and wanted some opinion on the following:

1. Stateless session is basically a wrapper around statefulsession and 
since per doc  statefulsession is not threadsafe is it  safe to assume 2 
threads cannot insert and run fireallrules to compare against a union of 
objects inserted by multiple threads without some synchronication on event 
insertion and ESP fireallrulesrules ? ( would the answer still hold despite a 
drools-camel endpoint reading and storing exchanges from multiple threads ? )

stateful sessions are thread safe, they just aren't
multi-threaded. Each of the working memory actions hold a lock, so
only one thread at a time can enter.

2. If in the above point we simplify the case where the rule uses the 
"from" keyword and reads from a cache or a Db ( is reading from
A cache supported out of the box ? ) then will drools bhaviour will be 
bound by the thread which invokes fireallrules() ?


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Re: [rules-users] Multiple threading

[Richard Calmbach]

Sorry to burst your bubble, but stateful knowledge sessions are most
definitely not thread-safe. I have seen hard evidence to this effect in the
form of incorrect execution results and log statements that clearly show
that two threads were interacting in unexpected ways. In a nutshell: Rule
consequences are not executed atomically. This can cause unexpected working
memory changes (e.g., fact insertion) to happen on one thread in one rule
consequence before another thread has finished executing another rule
consequence. Note that I'm not talking about whatever threads Drools may be
creating internally. I'm talking about application threads.

I have found synchronizing on the session object to be a reliable safeguard
against unwanted thread interactions. Basically, this way all external fact
insertions and calls to fireAllRules() are serialized.

If this is not supposed to be necessary (synchronizing on the session),
then there is a thread-safety bug in Drools.

-Richard

2012/2/10 Mark Proctor 

>  On 10/02/2012 03:36, Apache wrote:
>
> Hey,
> I am trying to get multiple threads to insert events and run rules against 
> the union of events inserted ( an as soon as they are inserted, a timer 
> drools thread kicking of fireallrules() is not an option because that would 
> introduce a delay ) and wanted some opinion on the following:
>
> 1. Stateless session is basically a wrapper around statefulsession and since 
> per doc  statefulsession is not threadsafe is it  safe to assume 2 threads 
> cannot insert and run fireallrules to compare against a union of objects 
> inserted by multiple threads without some synchronication on event insertion 
> and ESP fireallrulesrules ? ( would the answer still hold despite a 
> drools-camel endpoint reading and storing exchanges from multiple threads ? )
>
>  stateful sessions are thread safe, they just aren't multi-threaded. Each
> of the working memory actions hold a lock, so only one thread at a time can
> enter.
>
> 2. If in the above point we simplify the case where the rule uses the "from" 
> keyword and reads from a cache or a Db ( is reading from
> A cache supported out of the box ? ) then will drools bhaviour will be bound 
> by the thread which invokes fireallrules() ?
>
>
>
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>
>
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Re: [rules-users] Multiple threading

[Wolfgang Laun]

There is just one interpretation of "thread-safe": All operations on an
object are synchronized to avoid race conditions when two threads operate
concurrently on an object.

Therefore it is, for instance, possible for two different threads to call,
say, insert(): Locks ensure that one thread finishes the insertion before
the other one is permitted to enter the critical section.

Notice, also, that a method such as fireUntilHalt() would be useless if the
method would not guarantee proper synchronization while other threads (who
else?) insert or modify or retract.

Mark's statement "Each of the working memory actions hold a lock, so only
one thread at a time can enter." is somewhat misleading - there isn't one
lock "held" by "each of the WM actions". There is one lock to be acquired
and released by each action.

-W

On 10 February 2012 23:46, apache  wrote:

> Mark
>  the first link in my previous post says something contradictory to what
> you
> mentioned. I understand that one thread at a time can use the session just
> not 2 or more threads at the same time . Is that what you meant too ?
>
> --
> View this message in context:
> http://drools.46999.n3.nabble.com/rules-users-Multiple-threading-tp3731592p3733915.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
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Re: [rules-users] Multiple threading

[apache]

Mark
 the first link in my previous post says something contradictory to what you
mentioned. I understand that one thread at a time can use the session just
not 2 or more threads at the same time . Is that what you meant too ? 

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Re: [rules-users] Multiple threading

[Mark Proctor]

On 10/02/2012 03:36, Apache wrote:

Hey,
I am trying to get multiple threads to insert events and run rules against the 
union of events inserted ( an as soon as they are inserted, a timer drools 
thread kicking of fireallrules() is not an option because that would introduce 
a delay ) and wanted some opinion on the following:

1. Stateless session is basically a wrapper around statefulsession and since 
per doc  statefulsession is not threadsafe is it  safe to assume 2 threads 
cannot insert and run fireallrules to compare against a union of objects 
inserted by multiple threads without some synchronication on event insertion 
and ESP fireallrulesrules ? ( would the answer still hold despite a 
drools-camel endpoint reading and storing exchanges from multiple threads ? )
stateful sessions are thread safe, they just aren't multi-threaded. Each 
of the working memory actions hold a lock, so only one thread at a time 
can enter.


2. If in the above point we simplify the case where the rule uses the "from" 
keyword and reads from a cache or a Db ( is reading from
A cache supported out of the box ? ) then will drools bhaviour will be bound by 
the thread which invokes fireallrules() ?


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Re: [rules-users] Multiple threading

[apache]

http://docs.jboss.org/jbpm/v5.2/javadocs/org/drools/KnowledgeBase.html#getStatefulKnowledgeSessions%28%29

http://docs.jboss.org/jbpm/v5.2/javadocs/org/drools/runtime/StatelessKnowledgeSession.html

Any replies ?

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Re: [rules-users] Multiple threading

[Wolfgang Laun]

2012/2/10 Apache 

> Hey,
> I am trying to get multiple threads to insert events and run rules against
> the union of events inserted ( an as soon as they are inserted, a timer
> drools thread kicking of fireallrules() is not an option because that would
> introduce a delay ) and wanted some opinion on the following:
>
> 1. Stateless session is basically a wrapper around statefulsession and
> since per doc  statefulsession is not threadsafe


>From where did you learn this?
-W


> is it  safe to assume 2 threads cannot insert and run fireallrules to
> compare against a union of objects inserted by multiple threads without
> some synchronication on event insertion and ESP fireallrulesrules ? ( would
> the answer still hold despite a drools-camel endpoint reading and storing
> exchanges from multiple threads ? )
>
> 2. If in the above point we simplify the case where the rule uses the
> "from" keyword and reads from a cache or a Db ( is reading from
> A cache supported out of the box ? ) then will drools bhaviour will be
> bound by the thread which invokes fireallrules() ?
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[rules-users] Multiple threading

[Apache]

Hey,
I am trying to get multiple threads to insert events and run rules against the 
union of events inserted ( an as soon as they are inserted, a timer drools 
thread kicking of fireallrules() is not an option because that would introduce 
a delay ) and wanted some opinion on the following:

1. Stateless session is basically a wrapper around statefulsession and since 
per doc  statefulsession is not threadsafe is it  safe to assume 2 threads 
cannot insert and run fireallrules to compare against a union of objects 
inserted by multiple threads without some synchronication on event insertion 
and ESP fireallrulesrules ? ( would the answer still hold despite a 
drools-camel endpoint reading and storing exchanges from multiple threads ? )

2. If in the above point we simplify the case where the rule uses the "from" 
keyword and reads from a cache or a Db ( is reading from
A cache supported out of the box ? ) then will drools bhaviour will be bound by 
the thread which invokes fireallrules() ? ___
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