David T. Lewis: Very useful your explanation.

Gary: thanks too.

If fact, I did what you tell we. The problem was that the select()
invocation was inside a specific function of OpenDBX. From SqueakDBX the
only thing I can do is to call again that function, but this is very
different that only call select() function again.

So, what I change openDBX code from this:

        if( ( fd = PQsocket( (PGconn*) handle->generic ) ) == -1 )
        {
            conn->errtype = -1;
            return -ODBX_ERR_BACKEND;
        }

        FD_ZERO( &fds );
        FD_SET( fd, &fds );

        switch( select( fd + 1, &fds, NULL, NULL, timeout ) )



to


    do {

            if( ( fd = PQsocket( (PGconn*) handle->generic ) ) == -1 )
            {
                conn->errtype = -1;
                return -ODBX_ERR_BACKEND;
            }

            FD_ZERO( &fds );
            FD_SET( fd, &fds );

            rv = select( fd + 1, &fds, NULL, NULL, timeout );

        } while ((rv == -1) && (errno == EINTR));

        switch( rv )


And now It works perfect. It was difficult to reproduce because openDBX
tests where ok, but squeakDBX ones not. This is because of SqueakVM as you
explain me.

So, I am waiting openDBX author feedback about my code, but at least it
work!!!

Thanks for the help again.

Mariano


On Mon, Jan 26, 2009 at 8:11 PM, Gary Chambers <gazzaguru2 at btinternet.com>wrote:

> Indeed. We did some work with RS485 support for the Serial plugin... EINTRs
> happen all the time... recommended to retry (see Linux documentation around
> the web as to why). Obviously, in a plugin, the retry can happen quite
> quickly. Not sure how using FFI might respond.
>
> Regards, Gary.
>
> ----- Original Message ----- From: "David T. Lewis" <lewis at mail.msen.com>
> To: "The general-purpose Squeak developers list" <
> squeak-dev at lists.squeakfoundation.org>
> Sent: Monday, January 26, 2009 1:50 AM
> Subject: Re: [squeak-dev] Help needed with select() socket function and
> signalhandlers in squeakVM
>
>
>
>  On Sun, Jan 25, 2009 at 08:50:35PM -0200, Mariano Martinez Peck wrote:
>>
>>>
>>> Now, I have a problem with select() invocation. This function returns -1.
>>> And the printf of the errno (where select() stores the errors), says:
>>> "Error
>>> with select function: Interrupted system call" which means I am getting a
>>> EINTR error. If you see console, you can see something like this:
>>>
>>> timeval tv_usec value: 0
>>> timeval tv_sec value: 3
>>> timeval tv_usec value: 0
>>> timeval tv_sec value: 2
>>> timeval tv_usec value: 996000
>>> timeval tv_sec value: 3
>>> timeval tv_usec value: 0
>>> Error with select function: Interrupted system call
>>>
>>>
>>> I asked Norbert (openDBX author) and he tell me exactly this:
>>>
>>> "An interrupted system call is something very normal because signals can
>>> be
>>> sent
>>> at every time to the application, either by the system or by the user. I
>>> guess, in the Squeak code there is some signal handler installed, which
>>> does
>>> something if one of the defined signals arrive.
>>>
>>> What I will do is to hide the consequences (returning an error) by
>>> looking
>>> at
>>> the error value and reenter the select call if the system call is
>>> interrupted."
>>>
>>
>> Norbert is correct, and his solution of reentering the system call sounds
>> like the right thing to do.
>>
>>  All I know is squeakVM is written it SLANG and then that's transformed to
>>> C.
>>> So, squeakVM runs in C. So, there is where it can be a signal handler ?
>>> Is
>>> there some way to change that from squeak (image) ?
>>>
>>
>> Any interrupt handler will service interrupts for the entire VM, so this
>> is
>> not something that you would want to set up for a specific plugin. If one
>> plugin sets a signal handler, it affects all other plugins as well as the
>> VM itself.
>>
>> It is actually quite easy to experiment with setting signal handlers if
>> you are using a Unix VM and if you have OSProcess installed. For example,
>> if you want to handle the SIGQUIT signal, you can evualate the expression
>> 'OSProcess accessor forwardSigQuit' to get a Smalltalk semaphore that will
>> be
>> signalled each time the operating system sends a SIGQUIT (signal number 3)
>> to the VM. You can have a Squeak process that waits on the semaphore and
>> does
>> whatever you like.
>>
>> To be clear however, Norbert's explanation is correct regardless of how
>> the VM chooses to handle a signal. When a system call such as select is
>> interrupted, the application (your plugin) needs to check for this and
>> retry the system call.
>>
>> HTH,
>>
>> Dave
>>
>>
>>
>
>
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