SOAP - Problem with separate threads

[Andre Garzia]

Dave,

never, ever, use a wait command while network routines may be working.
The wait call will wreck them. If the problem is entering a race
condition, like, when one call is being placed, the other can't work.
This happens because libURL will queue requests to the same server, so
if you call the same server two times in a row without allowing it to
deal with the first request, you receive an "error previous request
not completed".

The idea of using a flag local variable is the best option, but do
that without the wait call. Work like this, if the flag is true,
postpone your operation to same later time. like

if isInUseFlag then
  -- call in use, postpone..
  send "doTheRequestAgain" to me in 2 secs
else
  -- do the request...
  put false into isInUseFlasg
end if

The hardest part is making a function that can re-request something
because if you're using send in time, you can't gather what were the
original parameters for the call by examining the pendingMessages.

If I were in your shoes, I'd work like this:

1) create a transaction queue. This would be an array where each web
request would be a member. Each array member stores all the info
needed to do a SOAP request.

2) I'd had a loop that would pick this array and work on the first
member, after dealing with this member, I'd remove it from the array.

3) Pooling the server then is just a matter of a simple send in time
that adds an element to the end of the array.

4) any function that would force a SOAP request would simply add an
element to the end of this array.

This way all your requests will work in order without the need of a
locking mechanism or a wait call. By having a 'callback' stored along
the data for each array member, you make your code as multi-taksing as
it can be in Rev.

Since all your calls are on the same place (the array pooling
function) you will not enter race conditions and your debugging will
be easier.

People with CS background will recognize this as nothing more than a
datastructure known as First-in First-Out queue. By making functions
like:

addToQueue pQueue, pElement -- add Element to Queue at last poisition.
takeElemFromQueue pQueue -- returns the first Element from queue and removes it.

You have created a generic queue function library that can be worked
in other projects.

Cheers
andre