[Xitami-Dev] LWRP : NonBlocking Sockets

[Kimman Balakrishnan]

Hello

Our document management application, comprising 8 different LRWP
modules, are written in either Visual Basic or C (console applications).

We noticed that when the Visual Basic applications are running and
waiting for requests, the machine tends to 'hang' - the applications
work ok but we could not start new instances of Explorer nor Internet
Explorer - any instance of these applications already running would work
fine. Furhter,  the 'open' common dialog of some applications would not
work.  The machine resource usage indicates over 60% free.

We have now changed the implementation in lrwplib.c to optionally use
non-blocking sockets. A new function, lrwp_setoptions has been added
with arguments :

    int non_blocking;        // whether to use non-blocking sockets
    int sleep_interval;       // sleep interval for timer - see below
    callback_proc;         // optional procedure to be called when
'select' indicates no data to read or cannot write
    callback_data;         // caller specific data

This function is called before making the 'connect' request to the
lrwplib.c. The default values are to use blocking sockets as implemented
currently. This ensures no 'break' for existing implementations. The
values of these options have been added as a separate structure and
appended to the existing struct LRWP.

If 'select' indicates that a read/write cannot be performed just yet,
the 'callback_proc', if non-NULL, is called. After this call, if the
sleep_interval is non-zero, the function invokes the 'sleep' function
with the argument, sleep_interval.

The callback_procedure can take over the responsibility for 'delay' or
it can let the lrwplib.c function handle it. In our case, the callback
function in Visual Basic makes a DoEvents call and lets the lrwplib.c
function handle the sleep.

With this implementation, the 'hang' problem seems to have been take
care of but it has yet to be tested on a wider range of machines. I was
able to run these applications and still work on several other
applications (Visual C++, Visual Basic and TextPad) while the requests
were being serviced. The machine on which this was tested is a Win98
(4.10.1998) Intel Pentium II box with 64 MB RAM.

The lrwp_connect2 modification was the main challenge since the quantum
of data expected is not easily predicted - it can either be OK or
CHALLENGE. Likewise after the response to the CHALLENGE, the response
could be either OK or REJECTED.

Comments and suggestions are invited.

Thanks

Kimman Balakrishnan
Imaging Solutions Pvt Ltd