Due to a major time constraint, need to stick with invoking rasphone.exe from my c program, rather than best approach of using RAS API's. From my code, when the rasphone pop's up a dialler window to the user, if the user click's on cancel button, i have to stop blocking another set of code.
Ultimately, i need to handle the rasphone returns to control my code flow based on the Success/Failure-Cancel. How to do this? Also, is there any other possibility for silent dialling without any popup?I hope no, as its discussed.
Related
I have an always one application, listening to a Kafka stream, and processing events. Events are part of a session. And I need to do calculations based off of a sessions data. I am running into a problem trying to correctly run my calculations due to the length of my sessions. 90% of my sessions are done after 5 minutes. 99% are done after 1 hour. Sessions may last more than a day, due to this being a real-time system, there is no determined end. Session are unique, and show never collide.
I am looking for a way where I can process a window multiple times, either with an initial wait period and processing any later events after that, or a pure process per event type structure. I will need to keep all previous events around(ListState), as well as previously processed values(ValueState).
I previously thought allowedLateness would allow me to do this, but it seems the lateness is only considered for when the event should have been processed, it does not extend an actual window. GlobalWindows may also work, but I am unsure if there is a way to process a window multiple times. I believe I can used an evictor with GlobalWindows to purge the Windows after a period of inactivity(although admittedly, I did not research this yet, because I was unsure of how to trigger a GlobalWindow multiple times.
Any suggestions on how to achieve what I am looking to do would be greatly appreciated, I would also be happy to clarify any points needed.
If SessionWindows won't do the job, then you can use GlobalWindows with a custom Trigger and Evictor. The Trigger interface has onElement and timer-based callbacks that can fire whenever and as often as you like. If you go down this route, then yes, you'll also need to implement an Evictor to dispose of elements when they are no longer needed.
The documentation and the source code are helpful when trying to understand how this all fits together.
I am designing an application which has the potential to hang while waiting for data from servers (either Database or internet) the problem is that I don't know how best to cope with the multitude of different places things may take time.
I am happy to display a 'loading' dialog to the user while access is happening but ideally I don't want this to flick up and disappear for short running operations.
Microsoft word appears to handle this quite nicely, as if you click a button and the operation takes a long time, after a few seconds you get a 'working..' dialog. The operation is still synchronous and you can't interrupt the operation. However if the same operation happens quickly you obviously don't get the dialog.
I am happy(ish) to devise some generic background worker thread handler and 99% of my data processing is already done in static atomic methods, but I would like to go best practice on this one if I can.
If anyone has patterns, code or suggestions I welcome them all
Cheers
I would definitely think asynchronously using a pattern with 2 events. The first "event" is that you actually got your data from wherever/whenever you had to wait for it. The second event is a delay timer. If you get your data before this timer pops, all is well and good. If not, THEN you pop up your "I'm busy" and allow them to cancel the request. Usually cancel just mean "ignore" when you finally get the response.
Microsoft word appears to handle this quite nicely, as if you click a button and the operation takes a long time, after a few seconds you get a 'working..' dialog. The operation is still synchronous and you can't interrupt the operation. However if the same operation happens quickly you obviously don't get the dialog.
If this is the behavior your want...
You could handle this, fairly easily, by wrapping a class around BackgroundWorker. Just time the start of the DoWork event, and the time to the first progress report. If a certain amount of time passes, you could show your dialog - otherwise, block (since it's a short process).
That being said, any time you're doing work that can be processed asynchronously, I'd recommend doing it that way. It's much nicer to never block your UI for a noticable interval, even if it's short. This becomes much simpler in .NET 4 (or 3.5 with Rx framework) by using the task parallel library.
Ideally you should be running any IO or non-UI processing either in a background thread or asynchronously to avoid locking up the UI.
We have a button that fires a command which goes to the server to do some validation. This is done asynchronously and if the validation is okay (i.e. the user has the correct permission), I want to show the SaveFileDialog.
However, this is not a user initiated action which means calling the SaveFileDialog.ShowDialog() method raises a "Dialog must be user initiated" exception.
Is there any way to make this work the way I want?
To other option is to launch the SaveFileDialog and make the request after the file has been selected. Not ideal but it works.
JD.
There is no work around after all it would be a pointless restriction if there were a work around.
I think your alternative design choice make sense. You might consider using a busy indicator with the message "Validating..." or some such whilst the async validation occurs then do what ever it is you would have done once the asyc operation completes.
I've been trying to work out how to cancel a long-running AD search in System.DirectoryServices.Protocols. Can anyone help?
I've looked at the supportControl/supportedCapabilities attributes on RootDSE and they don't contain the 1.3.6.1.1.8 OID so I think that means it doesn't support the LDAP CANCEL extended operation as defined here: https://www.rfc-editor.org/rfc/rfc3909
That leaves the original LDAP ABANDON command (see here for list). But there doesn't seem to be a matching DirectoryRequest Class.
Anyone have any ideas?
I think I've found my answer: whilst I was reading around your suggestion, Martin, I came across the Abort method on the LdapConnection class. I didn't expect to find it there: starting out from the LDAP documentation I'd expected to find it as just another LDAPMessage but the MS guys seem to have treated it as a special case. If anyone is familiar with a non-MS implementation of LDAP and can comment on whether the MS approach is typical, I'd appreciate it to improve my understanding.
I think, but I'm not positive, there is no asynch query with a cancel. It has an asynch property but it's to allow a collection to be filled, nothing to do with cancelling. The best I can offer is to put your query in a background worker thread and put an asynch callback that will deal with the answer when it comes back. If the user decides to cancel, you can just cancel the background worker thread. You'll free your app up, even if you haven't freed the ldap server up until it finishes it's query. You can find info on background worker threads at http://www.c-sharpcorner.com/UploadFile/LivMic/BGWorker07032007000515AM/BGWorker.aspx
Don't forget to call .Dispose() when cleaning up your active directory objects to prevent memory leaks.
If the query will produce many data also, you can abandon them through paging. Specify a PageResultRequestControl option in the query, giving a fairly low page size (IIUC, 1000 is the default page size). IIUC, you'll send new requests every time you got a page (passing cookies from one response into the next request). When you choose to cancel the query, send another request with zero expected results.
I'm sure there is a good (or at least decent) reason for this. What is it?
I think this is a brilliant question -
and I think there is need of a better
answer.
Surely the only reason is that there
is something in a framework somewhere
that isn't very thread-safe.
That "something" is almost every single instance member on every single control in System.Windows.Forms.
The MSDN documentation for many controls in System.Windows.Forms, if not all of them, say "Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe."
This means that instance members such as TextBox.Text {get; set;} are not reentrant.
Making each of those instance members thread safe could introduce a lot of overhead that most applications do not need. Instead the designers of the .Net framework decided, and I think correctly, that the burden of synchronizing access to forms controls from multiple threads should be put on the programmer.
[Edit]
Although this question only asks "why" here is a link to an article that explains "how":
How to: Make Thread-Safe Calls to Windows Forms Controls on MSDN
http://msdn.microsoft.com/en-us/library/ms171728.aspx
Because you can easily end up with a deadlock (among other issues).
For exmaple, your secondary thread could be trying to update the UI control, but the UI control will be waiting for a resource locked by the secondary thread to be released, so both threads end up waiting for each other to finish. As others have commented this situation is not unique to UI code, but is particularly common.
In other languages such as C++ you are free to try and do this (without an exception being thrown as in WinForms), but your application may freeze and stop responding should a deadlock occur.
Incidentally, you can easily tell the UI thread that you want to update a control, just create a delegate, then call the (asynchronous) BeginInvoke method on that control passing it your delegate. E.g.
myControl.BeginInvoke(myControl.UpdateFunction);
This is the equivalent to doing a C++/MFC PostMessage from a worker thread
Although it sounds reasonable Johns answer isn't correct. In fact even when using Invoke you're still not safe not running into dead-lock situations. When dealing with events fired on a background thread using Invoke might even lead to this problem.
The real reason has more to do with race conditions and lays back in ancient Win32 times. I can't explain the details here, the keywords are message pumps, WM_PAINT events and the subtle differences between "SEND" and "POST".
Further information can be found here here and here.
Back in 1.0/1.1 no exception was thrown during debugging, what you got instead was an intermittent run-time hanging scenario. Nice! :)
Therefore with 2.0 they made this scenario throw an exception and quite rightly so.
The actual reason for this is probably (as Adam Haile states) some kind of concurrency/locky issue.
Note that the normal .NET api (such as TextBox.Text = "Hello";) wraps SEND commands (that require immediate action) which can create issues if performed on separate thread from the one that actions the update. Using Invoke/BeginInvoke uses a POST instead which queues the action.
More information on SEND and POST here.
It is so that you don't have two things trying to update the control at the same time. (This could happen if the CPU switches to the other thread in the middle of a write/read)
Same reason you need to use mutexes (or some other synchronization) when accessing shared variables between multiple threads.
Edit:
In other languages such as C++ you are
free to try and do this (without an
exception being thrown as in
WinForms), but you'll end up learning
the hard way!
Ahh yes...I switch between C/C++ and C# and therefore was a little more generic then I should've been, sorry... He is correct, you can do this in C/C++, but it will come back to bite you!
There would also be the need to implement synchronization within update functions that are sensitive to being called simultaneously. Doing this for UI elements would be costly at both application and OS levels, and completely redundant for the vast majority of code.
Some APIs provide a way to change the current thread ownership of a system so you can temporarily (or permanently) update systems from other threads without needing to resort to inter-thread communication.
Hmm I'm not pretty sure but I think that when we have a progress controls like waiting bars, progress bars we can update their values from another thread and everything works great without any glitches.