On Tuesday 07 July 2009 20:41:54 sashee wrote:
> Maybe I don't see something, but I think it is much more simpler. Here it is:
>
> When the processing of RequestElement starts, the ClientRequest object
> is already activated, because FCPClient:305 activates all requests,
> and puts to the v List, and those object are the very same objects
> RequestElement works with. So they are initialized, but maybe the
> Fetch(Insert)Context isn't. So activate it. And also the EventProducer
> if not activated. As the constructor has the ObjectContainer object,
> it can activate. As I see this is used at ClientGet:785. invoked from
> RequestElement:122 , and it seems to be working.
Yes. But these objects may become deactivated shortly after the constructor
ends.
>
> The only problem seems to be that these listeners shouldn't be
> persisted, they aren't supposed to survive a restart. So I think I
> should create a mechanism for transient eventlisteners.
Which is pretty much what I was saying. You can't just add a listener to each
request because it may be deactivated. But if you add it at e.g. the FCPClient
level, you can get a callback while it is active.
>
> What you think about it?
>
> sashee
>
> On Tue, Jul 7, 2009 at 7:56 PM, Matthew
> Toseland<toad at amphibian.dyndns.org> wrote:
> > On Tuesday 07 July 2009 18:50:58 Matthew Toseland wrote:
> >> On Tuesday 07 July 2009 18:26:40 Matthew Toseland wrote:
> >> > ? ? ?public void addEventListener(ClientEventListener cel) {
> >> > + ? ? ? if(listeners==null){
> >> > + ? ? ? ? ? ? ? //Don't know how it can happen, but it did, and checking
> >> > for null isn't going to hurt anything
> >> > + ? ? ? ? ? ? ? listeners=new Vector<ClientEventListener>();
> >> > + ? ? ? }
> >> > ? ? ? ? if(cel != null)
> >> > ? ? ? ? ? ? listeners.addElement(cel);
> >> > ? ? ? ? else
> >> > ? ? ? ? ? ? throw new IllegalArgumentException("Adding a null
> >> > listener!");
> >> > ? ? ?}
> >> >
> >> > It can't happen for transient requests. For persistent requests, a
> >> > persistence-related bug in the code might well cause it to happen
> >> > however. :(
> >> >
> >> Okay, now I see what is going on ...
> >>
> >> + ? ? ? public RequestElement(ClientRequest clientRequest, int[] columns,
> >> String path, ObjectContainer container, boolean advancedModeEnabled,
> >> String[] priorityClasses, boolean isUpload, ToadletContext ctx) {
> >> ...
> >> + ? ? ? ? ? ? ? if (clientRequest instanceof ClientGet) {
> >> + ? ? ? ? ? ? ? ? ? ? ? if (((ClientGet)
> >> clientRequest).getFetchContext().eventProducer != null) ((ClientGet)
> >> clientRequest).getFetchContext().eventProducer.addEventListener(progressListener);
> >> + ? ? ? ? ? ? ? } else if (clientRequest instanceof ClientPutBase) {
> >> + ? ? ? ? ? ? ? ? ? ? ? if (((ClientPutBase)
> >> clientRequest).getInsertContext().eventProducer != null) ((ClientPutBase)
> >> clientRequest).getInsertContext().eventProducer.addEventListener(progressListener);
> >> + ? ? ? ? ? ? ? } else {
> >> + ? ? ? ? ? ? ? ? ? ? ? System.err.println("Dont know this type! type:" +
> >> clientRequest.getClass());
> >> + ? ? ? ? ? ? ? }
> >> + ? ? ? ? ? ? ?
> >> clientRequest.getClient().addRequestCompletionCallback(progressListener);
> >> + ? ? ? }
> >>
> >>
> >> Anything on the download/upload page is a persistent request. A persistent
> >> request is either persistence=reboot or persistence=forever, but the
> >> latter is far more common. These requests are *stored in a database*, and
> >> are not always in memory. Using them as variables will cause them to be
> >> pinned in memory but will not ensure they stay "activated" i.e. that all
> >> their fields are loaded and non-null. The only safe way to access them is
> >> to schedule a job on the database thread (the DBJobRunner, aka
> >> NodeClientCore). Hence, the SimpleEventProducer may well be null, and even
> >> if it isn't, it may not be activated, meaning the listeners array may be
> >> null.
> >>
> >> Hence subscribing to the SimpleEventProducer and listening for events is
> >> not going to be sufficient. You need to implement some sort of global
> >> hook, so that when an event is generated against a request in the global
> >> queue (only the global queue is shown on the downloads/uploads pages), you
> >> get a notification, at that point, while the request is still active.
> >>
> >> What you need to do is as follows:
> >> - FCPServer.globalRebootClient is the half of the global queue that is
> >> persistence=reboot, that is, the part that isn't persisted to the
> >> database. You can ignore it for all practical purposes, but you should
> >> really deal with it when you get around to it.
> >> - FCPServer.globalForeverClient is the half of the global queue that is
> >> persistence=forever, and in practice has almost all global requests
> >> (requests or inserts shown on the downloads/uploads pages). It is never
> >> deactivated.
> >> - This is an FCPClient.
> >> - You need to create a callback method and a registry of listeners on
> >> FCPClient that gets fed every FCP event, at the time it is created, along
> >> with the ClientRequest which created it. This happens in
> >> ClientGet.receive, ClientPutBase.receive, and probably that's about it;
> >> check the call hierarchy for the constructors for e.g.
> >> SimpleProgressMessage if you are concerned. This always happens on the
> >> database thread, or at least, if it's not on the database thread, it
> >> schedules a job on the database thread to send the message (e.g. in
> >> ClientPutBase.trySendProgressMessage). So call the callback at that point.
> >> - The callback should go to some sort of manager object, which determines
> >> which RequestElement(s) want the message. Or you can just register all of
> >> them but it will be slower that way.
> >> - Don't store the pointers, store the UID of the request (this is because
> >> we don't want to pin the request object in memory). This is an long value
> >> for a specific request in the database which doesn't change unless we
> >> defrag (which is an offline operation). You can get it by:
> >>
> >> container.ext().getID(<object>).
> >>
> >> Please let me know if you need any more information on this! The db4o zip
> >> file contains javadocs, you can get it from db4o.com, we use version 7.4.
> >>
> > Also, you should not store the ObjectContainer, and should not access the
> > database except on the database thread (i.e. when an ObjectContainer has
> > been passed in ultimately from a DBJob).
> >
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> >
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