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Re: Non-deterministic behavior of multithreaded software

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On 05-08-2011 PM 05:37, Victor Bazarov wrote:
> On 8/5/2011 5:40 AM, itt ium wrote:
>> I have recently modified a software from single threaded to
>> multithreaded design. In single threaded version, a connection fd was
>> read by single thread, so event were always delivered in order. Now
>> since multiple threads handle different events (on the same fd), the
>> events are sometimes delivered out of order.
>
> "Delivered" by whom, to where? Handling of events is one thing,
> delivering them is another. Do you need them processed in order, then
> don't parallelise their processing. If your events can be processed out
> of order but then need to be re-queued, then you need to mark each event
> (see below) for reassembling of the queue.
>
There is another module that receives the processed data and that data 
is delivered to the module out of order. Moreover We want to increase 
the message processing capacity per second  for the software.with a 
single threaded design, we have reached the maximum capacity (in terms 
of message processed per second). Please note we are running the 
software on a hexacore machine.
>  > Please note, on the
>> connection fd, events are received in proper order and this non-
>> deterministic behavior is introduced by my software only.
>>
>> Following are my doubt
>>
>> 1. How to handle such a situation
>
> Every event, when read from your 'fd' (whatever that is), needs to be
> wrapped in a package with the assigned ordinal number so that after
> processing it can be again placed in another queue _sorted_.
>

There are few more inputs here. My software is handing the call session. 
The problem occur, if event for a call are delivered out of order. I 
have modified the software such that message belonging to a call are 
processed by same thread, in this way ordering of events for the call 
state machine is maintained. But this has introduced a pinner thread 
that assign the messages to different worker threads based on a a hash 
function that take input as call ID.

1. Thread ID may not be uniformly distributed, any logic of work 
devision might load few thread.

2. A context switch is introduced because of pinner. Earlier a single 
thread was doing all the work (from reading from socket to delivering it 
to other modules.

>> 2. Is it a bad idea to have multiple threads for the same fd. If yes
>> than how to increase capacity of a software that receives large amount
>> of data on a single fd only.
>
> Are you guessing what can and cannot be parallelized? It's better to do
> a systematic analysis of your own software to see what improvement you
> can make by adding multithreading to it. There are many good/decent
> books on thread and designing for parallel execution, why don't you
> start with them?
>

I think, this is very generic comment, You can safely assume that  I 
know, what can be executed in parallel and I have been using pthread for 
quite sometime.

>>
>> Because of the relevance I am posting the message to following groups.
>>
>> comp.unix.programmer
>>
>> comp.programming.threads
>
> No, you're not. I'm reading this in 'comp.lang.c++'. Perhaps you
> multiposted, but that's a BAD IDEA(tm). If you have to use more than one
> newsgroup, *cross-post*.
>

My apologies and thanks for pointing this out. I will definitely try 
multiplying in future

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Thread

Non-deterministic behavior of multithreaded software itt ium <ittium@gmail.com> - 2011-08-05 02:40 -0700
  Re: Non-deterministic behavior of multithreaded software Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-05 08:07 -0400
    Re: Non-deterministic behavior of multithreaded software "Paul" <pchristor@yahoo.co.uk> - 2011-08-06 22:08 +0100
    Re: Non-deterministic behavior of multithreaded software ittium <ittium@gmail.com> - 2011-08-09 10:05 +0530
  Re: Non-deterministic behavior of multithreaded software Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-06 07:38 +0000
    Re: Non-deterministic behavior of multithreaded software ittium <ittium@gmail.com> - 2011-08-09 10:09 +0530

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