Using threads (pthreads) in a VFS module on Linux

Richard Sharpe realrichardsharpe at
Sun Sep 30 22:19:46 MDT 2012

On Sat, Sep 29, 2012 at 12:31 PM, Volker Lendecke
<Volker.Lendecke at> wrote:
> On Sat, Sep 29, 2012 at 01:45:45PM -0700, Richard Sharpe wrote:
>> At Samba XP during my presentation on the Samba VFS someone asked me
>> about whether or not you can really use threads in a VFS Module.
>> At that time I blithely answered yes. While the answer is true, in my
>> experience, at least for Linux, it is a little more complicated than
>> that.
>> If you use AIO, you should be aware that it uses signals. If you do
>> not disable the signals that Samba uses in your threads you risk nasty
>> things happening. For example, IO completions can silently disappear
>> if you have multiple outstanding AIO requests at any one time, which
>> after all, is the raison d'être of AIO. Windows does not like it when
>> it does not get a response for some IOs for a long period of time and
>> simply resets the connection.
>> The solution is to use pthread_sigmask and friends to switch off all
>> signals, or at least the ones Samba wants, before starting your
>> threads.
> Please be aware that neither aio_fork nor aio_pthread (now
> the default) use signals. The Posix API is now done in the
> aio_posix module. Please also be aware that our internal
> messaging system uses SIGUSR1, but this use might possibly
> go away relatively soon (not for 4.0 though).

Heh. Thanks. I did not think to look for aio modules :-( Both aio_fork
and aio_pthread are available as modules in 3.6.x while aio_fork is
available as a module in 3.5.x by the look of things.

So, you will still probably want to switch off signals like SIGUSR1.
In our case we were using the default AIO support.

Richard Sharpe

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