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From Stephen Powis <spo...@salesforce.com>
Subject Re: thread safe output collector
Date Thu, 28 Apr 2016 15:58:53 GMT
So the Spout documentation (assuming its correct...) here (
http://storm.apache.org/releases/current/Concepts.html#spouts) mentions
this:

"The main method on spouts is nextTuple. nextTuple either emits a new tuple
into the topology or simply returns if there are no new tuples to emit. *It
is imperative that nextTuple does not block for any spout implementation,
because Storm calls all the spout methods on the same thread.*"

When developing a custom spout we interpreted it to mean that any "real
work" done by a spout should be done in a separate thread, and decided on
the following pattern which seems some what relevant to what you are trying
to do in your bolts.

On Spout prepare, we create a concurrent/thread safe queue.  We then create
a new Thread passing it a reference to our thread safe queue.  This thread
handles finding new data that needs to be emitted.  When that thread finds
data, it adds it to the shared queue.  When the spout's nextTuple() method
is called, it looks for data on the shared queue and emits it.

I imagine doing async processing in a bolt using one or more threads could
work with a similar pattern.  On prepare you setup your thread(s) with
references to a shared queue.  The bolt passes work to be completed to the
thread(s), the thread(s) communicate back to the bolt the result via a
shared queue.  Add in the concept of tick tuples to ensure your bolt checks
for completed work on a regular basis?

Is there a better way to do this?

On Thu, Apr 28, 2016 at 11:22 AM, Julien Nioche <
lists.digitalpebble@gmail.com> wrote:

> Thanks for the clarification
>
> On 28 April 2016 at 15:12, P. Taylor Goetz <ptgoetz@gmail.com> wrote:
>
>> The documentation is wrong. See:
>>
>> https://issues.apache.org/jira/browse/STORM-841
>>
>> At some point it looks like the change made there got reverted. I will
>> reopen it to make sure the documentation is corrected.
>>
>> OutputCollector is NOT thread-safe.
>>
>> -Taylor
>>
>> On Apr 28, 2016, at 9:06 AM, Stephen Powis <spowis@salesforce.com> wrote:
>>
>> "Its perfectly fine to launch new threads in bolts that do processing
>> asynchronously. OutputCollector
>> <http://storm.apache.org/releases/current/javadocs/org/apache/storm/task/OutputCollector.html>
>> is thread-safe and can be called at any time."
>>
>>
>> From the docs for 0.9.6:
>> http://storm.apache.org/releases/0.9.6/Concepts.html#bolts
>>
>> On Thu, Apr 28, 2016 at 9:03 AM, P. Taylor Goetz <ptgoetz@gmail.com>
>> wrote:
>>
>>> IIRC there was discussion about making it thread safe, but I don't
>>> believe it was implemented.
>>>
>>> -Taylor
>>>
>>> On Apr 28, 2016, at 3:52 AM, Julien Nioche <
>>> lists.digitalpebble@gmail.com> wrote:
>>>
>>> Hi Stephen
>>>
>>> I asked the same question in February but did not get a reply
>>>
>>>
>>> https://mail-archives.apache.org/mod_mbox/storm-user/201602.mbox/%3CCA+-fM0urPf3FUERoZywPzmxu-KDbGF-Zj3wbYr8evsAQJC6u_g@mail.gmail.com%3E
>>>
>>> Anyone who could confirm this?
>>>
>>> Thanks
>>>
>>> On 27 April 2016 at 14:05, Steven Lewis <Steven.Lewis@walmart.com>
>>> wrote:
>>>
>>>> I have conflicting information, and have not checked personally but has
>>>> the output collector finally been made thread safe for emitting in version
>>>> 1.0 or 0.10? I know it was a huge problem in 0.9.5 when trying to do
>>>> threading in a bolt for async future calls and emitting once it returns.
>>>>
>>>> This email and any files transmitted with it are confidential and
>>>> intended solely for the individual or entity to whom they are addressed.
If
>>>> you have received this email in error destroy it immediately. *** Walmart
>>>> Confidential ***
>>>>
>>>
>>>
>>>
>>> --
>>>
>>> *Open Source Solutions for Text Engineering*
>>>
>>> http://www.digitalpebble.com
>>> http://digitalpebble.blogspot.com/
>>> #digitalpebble <http://twitter.com/digitalpebble>
>>>
>>>
>>
>>
>
>
> --
>
> *Open Source Solutions for Text Engineering*
>
> http://www.digitalpebble.com
> http://digitalpebble.blogspot.com/
> #digitalpebble <http://twitter.com/digitalpebble>
>

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