[SR-Users] Keep Number of Messages per Source

[AliReza Khoshgoftar Monfared]

Thanks very much Daniel and Alex,

I switched to the atomic increase ("$var(x) = $shtinc(a=>x);"),

My attempt to get automatic expiration and resetting of values to 0 by
doing "modparam("htable", "htable", "message_counters=>size=10;
autoexpire=10;initval=0;updateexpire=0;")" was not successful (values
persisted), but I could achieve it by having a timer route block (using
"rtimer") that expires every 10 second and calling
"sht_rm_name_re("message_counters=>.*");" inside it (in case that it may
help people who will get into the same issue later)


All the best,
Alireza


On Wed, Aug 13, 2014 at 10:58 AM, Daniel-Constantin Mierla <
miconda at gmail.com> wrote:

>
> On 13/08/14 16:24, Alex Balashov wrote:
>
>> On 08/13/2014 10:21 AM, AliReza Khoshgoftar Monfared wrote:
>>
>>  Another concern is that, if I specify a number of child processes in my
>>> config (e.g. children=4), then will it be safe to increment the hash
>>> table entries in the route block upon receipt of messages? i.e will the
>>> table entries that reside in the shared memory be precise? or do I need
>>> to lock/unlock them while updating?
>>>
>>
>> htable operations are thread-safe, as implemented under the hood. You do
>> not explicitly need to lock anything.
>>
>>  While that is true for htable (direct) operations, one should be careful
> when using hash table items in expressions.
>
> So:
>
> - next is an atomic increment of $sht(a=>x)
>
> $var(x) = $shtinc(a=>x);
>
> - but next might rise races:
>
> $sht(a=>x) = $sht(a=>x) + 1;
>
> because first the value is read, an add expression is evaluated and then
> the item in hash table is set to new value. During the evaluation of the
> expression, the current process can lose CPU, and another process can
> update the item. So you can make it safer with:
>
> sht_lock("a=>x");
> $sht(a=>x) = $sht(a=>x) + 1;
> sht_unlock("a=>x");
>
> Cheers,
> Daniel
>
>
> --
> Daniel-Constantin Mierla
> http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
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