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ParallelGateway for Service Task

lojian

As we know that ParallelGateway could fork all outgoing sequence flows, create one concurrent execution for each sequence flow.
My question here is, ”concurrent" here means "each flow is running in different thread" ?

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Comments

jbarrez

No, Activiti does not spawn new threads. All outgoing sequence flow are taken in the same transaction (plus all automatic paths that follow). If you were to do that in different threads, this would cause unneeded delays and locking problems.

lojian

Thank you very much!

actuser

Hi,
Just raising this question again. Can using "asynchronous continuations" provide this type of 'concurrency' for service tasks on separate sequence flows of a parallel gateway, i.e. the service tasks will be executed concurrently in different background threads ??

Thanks..

trademak

Hi,

We're currently implementing a patch for this.
Right now you can only have one async continuation after the parallel gateway.
So if you have multiple outgoing paths with async continuations, you'll be running into errors.
But we have a patch on one of the branches right now that overcomes this. So it will certainly be in the Activiti 5.9 release.

Best regards,

actuser

Thanks for that info. Will there be any limitations with this fix like, for example, imposing a limit on the number of asynchronous continuations (e.g. 2) that can be modelled after a parallel gateway ? We have a requirement to run several service tasks concurrently in a part of our workflow, so at the moment this seems to be the only way possible that we could meet that requirement using the activiti workflow engine.

jsher

Hi,

I also would like to see the removal of the restriction on number of async continuations after a parallel gateway. Hopefully the fix will make it into next release as you say.

A related question… are there any similar restrictions on
(i) the number of concurrent user tasks after a parallel gateway ?
(ii) the the number of concurrent receive tasks after a parallel gateway ?

Many thanks
James

trademak

Hi,

No after the patch there will be no limitations.

Best regards,

ronald_van_kuij

no limitations besides maybe the number of concurrent job executors?

actuser

Hi,
Is there any way I can get the code for this patch in order to merge it into our Activiti 5.8 code base ? I'd like to do some testing with our model before the Activiti 5.9 release.
Thanks again.
John

actuser

Hi Tijs,
Is it still planned to include this patch in the 5.9 release ? From a preliminary test using the trunk code it seems that it is still not possible to successfully run multiple "asynchronous continuations" in their own separate thread in the parallel gateway.
Regards..
John

trademak

Hi John,

Yes this should be possible in the 5.9 release. Can you share a test that doesn't work as it's supposed to?

Best regards,

actuser

Hi Tijs,
I will check this with the developer. The initial test showed that the 'Asynchronous' tasks on the Gateway executed successfully, but they executed "in-sequence" rather than concurrently. He said that the same thread was reused for each task execution, so maybe it was a configuration problem in our test.
I will come back to you on this…
Cheers.
John

actuser

Hi Tijs,
Does the threading behaviour differ when using the "StandaloneInMemProcessEngineConfiguration" ? In this test the same thread from the thread-pool is used to execute the 'asynchronous continuation' task logic (just a system.out), so they execute in sequence. This is the same behaviour as for 'synchronous' tasks.
Just to clarify - should the patch allow the running of "Asynchronous Continuation" tasks on a gateway in their own separate thread ? So we should see multiple threads running concurrently in the gateway ?

/John.

guy_gavriely

5.9 is in two weeks, so I guess this feature should be included already, can someone confirm? I've checked out the code but still not sure if its there.
Thanks,
Guy

feecon

Hi,

I get the latest snapshot of Activiti 5.9, and I run sucessfully some workflow with asynchronous tasks and parallel gateway.
However when I grow up the bench by starting 1000 workflows with the same ProcessEngine and changing the size of the thread pool size to 1024 (min = max = queuesize) in the DefaultJobExecutor class, I get some racing exceptions:

SEVERE: Error while closing command context
java.lang.NullPointerException
at org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionCreateScope.execute(AtomicOperationTransitionCreateScope.java:34)
at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:77)
at org.activiti.engine.impl.jobexecutor.AsyncContinuationJobHandler.execute(AsyncContinuationJobHandler.java:35)
at org.activiti.engine.impl.persistence.entity.JobEntity.execute(JobEntity.java:78)
at org.activiti.engine.impl.persistence.entity.MessageEntity.execute(MessageEntity.java:29)
at org.activiti.engine.impl.cmd.ExecuteJobsCmd.execute(ExecuteJobsCmd.java:67)
at org.activiti.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:24)
at org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:42)
at org.activiti.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:42)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:130)
at org.activiti.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:40)
at org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:33)
at org.activiti.engine.impl.jobexecutor.ExecuteJobsRunnable.run(ExecuteJobsRunnable.java:46)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)

And some times:

SEVERE: Error while closing command context
org.activiti.engine.ActivitiException: No job found with id '3323'
at org.activiti.engine.impl.cmd.ExecuteJobsCmd.execute(ExecuteJobsCmd.java:58)
at org.activiti.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:24)
at org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:42)
at org.activiti.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:42)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:130)
at org.activiti.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:40)
at org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:33)
at org.activiti.engine.impl.jobexecutor.ExecuteJobsRunnable.run(ExecuteJobsRunnable.java:46)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)

I guess this exceptions don't appear with the default configuration because there are only 10 threads running concurrently.
Are you aware of this issues ?
Thanks

feecon

I try to minimize an unit test to reproduce these previous exceptions.
You can change variables NB_PARALLEL_WORKFLOWS and threadPoolSize.

Hoping it can help…

testParallelGateway.zip

BenchMarkTest.png

falko_menge

no limitations besides maybe the number of concurrent job executors?

You're right. The number of Job Executor theads limits the number of jobs executed in parallel.

Does the threading behaviour differ when using the "StandaloneInMemProcessEngineConfiguration" ?

No.

I try to minimize an unit test to reproduce these previous exceptions.

Your tasks have not set activiti:exclusive="false". Hence, one JobExecutor thread will execute all jobs sequentially:

Since activiti 5.9, the JobExecutor makes sure that jobs from a single process instance are never executed concurrently.
[…]
All asynchronous continuations and timer events are thus exclusive by default. In addition, if you want a job to be non-exclusive, you can configure it as such using activiti:exclusive="false".

See also: Activiti Userguide: Exclusive Jobs

However, this doesn't explain the exceptions you got.