FreeBSD deadlock (with fork?)

David Naylor naylor.b.david at
Thu Sep 18 16:57:52 UTC 2008

On Thursday 18 September 2008 15:33:52 Tom Evans wrote:
> On Thu, 2008-09-18 at 06:31 +0200, David Naylor wrote:
> > Hi,
> >
> > I have a program that spawns a lot of subprocesses (with pipes open) from
> > multiple threads.  The problem is the program often deadlocks, but not
> > consistently.  Sometimes the program can run over 5 times to competition
> > without incidence and yet othertimes it locks within a few seconds.
> Do you create threads, which then fork(), or do you fork() and then create
> threads?

I have many threads that then fork.  (aka forking threads).  

> I think the former will not work..

Is there any reason for this and is this a FreeBSD limitation or a general 

The problem is that my program has to have threads (or something similar) 
since it handles lots of IO bound processes concurrently so is there a 
work-a-round for this problem?

I could limit the forking to a single thread (which I tried and did not work) 
but perhaps I need to have it fork from the master thread?

One option I considered was forking a 'slave' program that then does all the 
forking but that will become exceedingly complex (with the communication 
between the 'slave' and the threads).  

Lastly, how does GUIs, such as Qt, handle forking since they are threaded and 
some do fork?  
> Cheers
> Tom


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