Beeing able to dispatch events while we are dispatching an event is
the expected behaviour. ActionScript doesn't have threads, so it's
threadsafe per definition. In other words, it never happens, that an
event interrupts a running method. If you dispatch an event while you
are in another event handler, the new event is completely handled
before the remaining handlers of the initial event are called. It's
just simple method calls.
1 dispatch event 1
2 handle event 1
3 dispatch event 2
4 handle event 2
5 handle event 2
6handle event 1
7handle event 1
So what is the exact problem you see? An exception in line 2 doesn't
stop the rest of the handling?
Cheers,
Ralf.
On 11/4/06, ncr100 <[EMAIL PROTECTED]> wrote:
> This is a complex one.
>
> Summary:
>
> I believe I'm not confused with try/catch, but am surprised that the
> EventDispatcher assumes our code is reentrant. Reentrant like the
> EventDispatcher is dispatching a system Event in the middle of me
> handling other events. So we're vulnerable to reentrant callbacks
> when we call EventDispatcher.dispatchEvent.
>
> Details:
>
> Normally when an null dereference happens an Error is propagated up
> the call stack to a catch handler.
>
> The bug is this: if in the middle of this call stack there happens to
> be an EventDispatcher.dispatchEvent call and the null pointer happens
> somewhere inside one of the listeners, then the Flash VM runtime
> thingy / implementation of dispatchEvent() itself seems to catch &
> handle the Error, and takes the opportunity to dispatch a pending
> Events. In my case I've seen a ProgressEvent.SOCKET_DATA being
> dispatched because my server pumped out some data to me really
> quickly, though I assume any pending Event could be dispatched.
>
> This really causes havoc because our methods aren't reentrant; flash
> isn't multithreaded afaik and we don't think we have to write
> everything thread-safe.
>
> Here's an illustration I will walk through. At the start of the stack
> our DTVSocket.onSocketConnect listens for an
> ProgressEvent.SOCKET_DATA, and just got one. Notice for now the
> EventDispatcher [no source] in the middle of the stack trace. Capping
> off the stack trace, see our TextUtil.setText method ... it is doing
> something bad, and has just triggered a null pointer exception!
>
> dtv.util::TextUtil$/setText (BANG! null pointer exception)
> MarbachViewer/MarbachViewer::createChannelCanvas
> MarbachViewer/MarbachViewer::subscribeToChannel
> MarbachViewer/MarbachViewer::onConnected
> flash.events::EventDispatcher/flash.events:EventDispatcher::dispatchEventFunction
> [no source]
> flash.events::EventDispatcher/dispatchEvent [no source]
> dtv.util::DTVSocket/dtv.util:DTVSocket::dispatchOnConnectedEvent
> dtv.util::DTVSocket/dtv.util:DTVSocket::onReceivedSessionTicket
> Function/http://adobe.com/AS3/2006/builtin::call [no source]
> dtv.util::DTVSocket/dtv.util:DTVSocket::onJSON
> dtv.util::DTVSocket/dtv.util:DTVSocket::onData
> dtv.util::DTVSocket/dtv.util:DTVSocket::onSocketData
>
>
> Now notice in this second shorter trace the stack has been unwound up
> to the dispatchEvent, but no further. onSocketData was just passed a
> second, new ProgressEvent.SOCKET_DATA. It must be that
> EventDispatcher.dispatchEvent caught my setText's null pointer
> exception and dispatched some additional socket data to my
> ProgressEvent.SOCKET_DATA listener. onSocketData is not thread safe.
> and bad stuff will happen very soon after in our code.
>
> dtv.util::DTVSocket/dtv.util:DTVSocket::onSocketData(WHOA! Not good)
> flash.events::EventDispatcher/flash.events:EventDispatcher::dispatchEventFunction
> [no source]
> flash.events::EventDispatcher/dispatchEvent [no source]
> dtv.util::DTVSocket/dtv.util:DTVSocket::dispatchOnConnectedEvent
> dtv.util::DTVSocket/dtv.util:DTVSocket::onReceivedSessionTicket
> Function/http://adobe.com/AS3/2006/builtin::call [no source]
> dtv.util::DTVSocket/dtv.util:DTVSocket::onJSON
> dtv.util::DTVSocket/dtv.util:DTVSocket::onData
> dtv.util::DTVSocket/dtv.util:DTVSocket::onSocketData
>
>
> So the deal is this: Beware of event listener entry-points being
> called in a reentrant fashion if your app is handling an exception.
> Kind of like someone hitting you when you're down, flash is asking for
> your app to do stuff when it's crippled.
>
> A solution is to wrap the guts of all entry points in try/catch
> handlers. Or maybe only for high-frequency entry points.
>
> I looked thru these links for insight, perhaps hints indicating this
> kind of behavior but didn't find it:
> http://livedocs.macromedia.com/flex/2/docs/wwhelp/wwhimpl/js/html/wwhelp.htm?href=1890.html
> http://livedocs.macromedia.com/flex/2/langref/statements.html#try..catch..finally
>
> Happy November!
> Nick
>
>
>
>
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