My application has background threads that communicate with our weather radar
hardware and need to notify all web sessions of status changes (e.g. the
position of the antenna, the status of the transmitter).
I have tried using both WServer::post() as well as signal/slot - each has their
advantages and disadvantages.
Using WServer::post
I've been using WServer::post(), but the callback function doesn't take any
arguments, so the notified session has to retrieve the status, and then decode
it. Note if I want to send multiple arguments, I have to encode them into a
StatusEvent, and the session needs to decode the StatusEvent. (This technique
was shamelessly borrowed from the Wt simplechat example).
===========================
Using signal and slots
I have some older code that is using Wt signals and slots. I liked that I
could send multiple parameters to a slot, but the UpdateLock caused me problems
- I needed to run one copy of the hardware polling thread per session, rather
than a single instance.
===========================
Questions:
1) Is there any way to send multiple parameters using WServer::post()?
2) How should I use signal/slot from a background boost thread to notify
multiple sessions?
My current code looks like:
app = Wt::WApplication::Instance()
Wt::WApplication::UpdateLock lock app->getUpdateLock();
logSignal_.emit(text);
app->triggerUpdate(); // push the changes to the browser
Do I need to call logSignal_.emit(text) multiple times, once for each session
that needs to be notified? Or do I need to lock all sessions, before calling
logSignal_.emit(text) ?
3) Is there any other mechanism I should use to send notifications with
multiple parameters from a polling thread to multiple sessions?
===========================
FYI, using WServer::post() the sequence of calls is:
<Session>
statusServer_.registerCallback(
this, wApp->bind( boost::bind( &SystemStatus_UI::statusEventCallback,
this)), ids)
<background thread>:
StatusServer::postStatusEvent(const StatusEvent &event)
WServer:post(sessionId, callback)
<Session>
SystemStatus_UI::statusEventCallback() // called from WServer::post()
event = statusServer_.getEvent(this)
processStatusEvent(event)
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