Hi Jeff,
On Thu, Oct 19, 2017 at 10:28 AM, Jeffrey Kain via 4D_Tech <
4d_tech@lists.4d.com> wrote:
> ...
>
all it's doing is waiting for a relatively rare condition to happen (and a
> record to appear in this table). It might happen at most once or twice per
> day, maybe only once every few days, but when it happens it has to be dealt
> with immediately. It's such a waste to be constantly querying for a record
> that 99999 times out of 100000 won't exist.
>
An approach I use in these cases is (I'm using pseudo code and this off the
top of my head):
// Handle_rare_condition (critical param{;internal param})
Case of
:(Count parameters=1)
// Write $1 to the [Message table}
$id:=Execute on server(Current method name;0;Current method name;$1;Current
process;*)
Resume process($id)
:(Count parameters=2) // this part is executing on the server
$done:=false
While(Not($done))
All Records([Message table])
Loop ([Message table]) -- do important stuff
Pause process(Current process)
End while
End case
When Handle_rare_condition is called with one param it writes that param
to the Message Table. Then it calls itself on the server. Execute on server
will either start the process, if it isn't already there, or since I
included the trailing * simply return the id of the existing process, which
if it exists is probably paused. Resume process($id) is ignored if the
process isn't paused (like when you just created it). Otherwise it wakes it
up.
On the server side $1 is pretty much ignored in this case. $2 might be
useful (I use this same form on Clients for spawning processes so knowing
the parent process number can be useful for messaging). In this case you
could make $1 a magic number of some sort to indicate the part of the code
running on the server. Or you could write the [Message table] record first
and then call this method without any params to initiate it and the parent
process as $1 to indicate the server code.
Whatever, the bottom part of the method starts a loop on the server which
sounds like it could get all records for [Message table], loop them and do
the important stuff. Then just go back to sleep. As someone else suggested
this could be called from a trigger on [Message table] to run whenever one
of those records was created.
This would not involve any queries.
I like putting the spawning and execution of server side methods in one
method. All the important stuff is in one place.
--
Kirk Brooks
San Francisco, CA
=======================
*The only thing necessary for the triumph of evil is for good men to do
nothing.*
*- Edmund Burke*
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