Inter Process Synchronisation

Resit Sahin resit.sahin at
Tue Jun 5 12:15:26 UTC 2012

Hello Everybody,

I am working on a multi process system. I have 10 or more processes 
(that are created with fork) and i want to synchronise them. There is a 
data structure which must be shared among the processes. The data 
structure contains statistics about some users which are more then some 
thousands. Each process needs to "read from" / "write to" this data 
structure thousands of times in a second. They all may need to update it 
500.000 times a second in total.  This is the scenario i need to build.

I am using NUMA architecture and ia64 CPUs like E5506.

I have investigated the options i have in FreeBSD and come up with few 
solutions. I am already using sockets for inter-process communication 
but it does not seem to be suitable for the above scenario. It is very 

The most suitable way seems to create a shared memory between the 
processes. The question is how to synchronise the access to the memory:

I have found two solutions for synchronisation. One is mutexes and  
other is semaphores.

The mutexes works only between threads but not between processes. Is 
there any support for inter process mutexes in FreeBSD 8.2 ?

The second option is semaphores. There are two types of semaphores, they 
are named semaphores and the memory based semaphores. Memory based 
semaphores seem to be a better option but they do not support inter 
process operation in FreeBSD 8.2 .

The only option seems to be using named semaphores and locking the whole 
data structure for each access. Would it be feasible to use named 
semaphores for locking 500.000 times a second?

I have read about atomic operations here: 

Would atomic operations be an option in my case?

The manual page says :

"On the i386 architecture, the cache coherency
      model requires that the hardware perform this task, thus the atomic oper-
      ations are atomic across multiple processors.  On the ia64 architecture,
      coherency is only guaranteed for pages that are configured to using a
      caching policy of either uncached or write back."

Is it safe to use named semaphores for*ia64* architecture ? Does FreeBSD 
8.2 support interprocess locking for ia64 architecture?

Kind Regards
Res,i S,ahin

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