What I want to do feels like sending av event from one module to another (like pressing a button). But as I have searched it seems that it should be done in an other way becuase I haven't found any standard way to send av event trigger/notification.
My simple model consists of two mudules, 1 Generator and 1 Controller. I want the Generator to be able to set an internal boolean in the Controller to true (indicating that there has been a registration on a sensor). The controller has a thread that acts if there has been a registration since last time and then resets the bool to false (effectively ignoring and discarding more sensor registrations during the 5 second wait).
if(sensor_activity)
{
doStuff();
wait(5, SC_SEC);
sensor_activity = 0;
}
How should I send my signal from Generator to Controller?
Use a buffer. It will trigger even if u write the value that it already has.
There are so many ways this can be done.
Systemc is basically C++. So generator can call a public function of controller, which will notify an internal event, which will trigger required thread.
Make a process in controller sensitive to a port, which will notify an internal event, which will trigger required thread. Write to the port from generator.
Declare a global sc_event variable. Now notify it in generator and use it to trigger the thread in controller.
Related
I have a dashboard with a list of items and a finite number of users. I want to show "an item is being edited" near said item to avoid simultaneous edits and overwrites of data.
This seems to me like updating a flag in the database and relatively simple signalr implementation with the javascript simply adding/removing a css class.
I have seen this:
Prevent multiple people from editing the same form
which describes a method with posting every X minutes and clearing the flag from the database when there are no more update messages from the user.
The issue is:
I was wondering if there was a signalr method (like disconnect; i know it exists but I don't know if it fits this scenario) to do that elegantly rather than running a timer function. If so, is it possible for the server to miss the event and permanently leave the flagged as "editing" when it is not?
you could implement a hub for this, here is a example:
public class ItemAccessHub : Hub
{
public override Task OnConnectedAsync()
{
// your logic to lock the object, set a state in the db
return base.OnConnectedAsync();
}
public override Task OnDisconnectedAsync(Exception exception)
{
// your logic to unlock the object
return base.OnDisconnectedAsync(exception);
}
}
to get information from the query you can access the HttpContext:
Context.GetHttpContext().Request.Query.TryGetValue("item-id", out var itemId)
so you could start a connection when the user is accessing the form and send the id of the item in the query:
/hub/itemAccess?item-id=ITEM_ID
and when the user closes the form then disconnect the connection.
with this method the item is also unlocked when the user loses his network connection.
the on disconnect method is allays invoked when a client disconnects, so you can do your clean up in this method.
in this hub you can than also implement the update function
i hope this is what you are looking for
I'm building a server and a client for a chat that runs on Tcp and Sockets, I want the client to handle more than one connection (to servers) so I made a class called "Client" to manage the async connection, so that I can run more instances at the same time like:
Dim ConnectionToServer1 as new Client
Dim ConnectionToServer2 as new Client
Since it's async when the the "connection" receives a message it generates an event (AsyncCallback) where I can convert the received bytes into a string.
The problem is: I've tried to set this string to a RichTextBox on my Form from inside the Client class, but nothing happens, I've tried to create a delegate in the form code but nothing works, the only way I was able to put the received message in the RichTextBox is by creating a public variable called LastMessage in the Client class where the last message is stored (every time it receives a message, the sub overrides the string), and then running a thread created by the Form which keeps checking for data (since the thread has been created by the form it has access to the controls, including the RichTextBox, right?)
Although I find this a bit clunky, is there any other way (through delegates maybe?) I can do it?
Here's some code:
Client class: http://pastebin.com/GF9um8Ss
Form code: http://pastebin.com/xW7mDj8j
Sounds like you started down all the right paths.
Now, on threaded applications one of the challenges that you will face is you can have tons of worker threads, but only the main, UI thread can actually make any updates to the UI. So keeping that in mind, if you have async code that needs to update the ui you will need to use what is effectively a delegate.
You can do this using tasks these days a lot easier, so read up on the Task Parallel Library, but essentially you need a delegate/task that is marshaled to run on the ui thread to handle the UI updates.
Set this global property as false
Control.CheckForIllegalCrossThreadCalls = false
this will let you edit any control of your form from any thread
My purpose is as follows: I want to create a deferred calling method. I might need to create a block for this, but I'm not sure. Can you explain me how to create a block for this?
This is the code:
- (IBAction)buyItem:(id)sender {
BOOL purchase = ... /*call purchase method use block*/
}
In this method I make a purchase and after the purchase has completed successfully I want to get result in my variable purchase.
To be more clear:
Step 1: Call the buyItem method.
Step 2: Wait for a response to the purchase (I've omitted the actual methods for the purchase)
Step 3: After the StoreKit object return a response about the purchase, write a value into the variable purchase.
Step 4: After writing the value into purchase, my method buyItem completes execution (go to the } and release).
My question is not about StoreKit specifically (meaning the StoreKit response method - this is an example only). The purchase variable is an example, too. For this variable I will use a data model and it will change after the deferred method executes.
Thanks all!
You do need a block, but maybe a different kind than you're thinking about. You don't need a 'closure', you need a function that will block until it receives the response from the store kit/server.
You can just write a normal buyItem method, but inside you either make a synchronous call to store kit, or if that's not possible, you use threading techniques to achieve what you want. For example, you could wait on a condition variable and then signal it when the store kit call returns.
For both cases, you'll want to perform the 'buyItem' call on a thread other than the UI thread, otherwise your UI will freeze. Given that constraint (if you're even dealing with a UI), I would say this entire approach doesn't make sense. Instead, you'll want to launch the store kit call, set some indicator or spinner or something in your UI, and then when the store kit call returns, unset the spinner or whatever. Make sense?
Inside ClassA:
-(void)authenticateUser
{
authenticate_Obj = [classB_Obj authenticateMobileUser];
}
Inside ClassB:
-(AuthenticateObj*)authenticateMobileUser
{
[mobile_Obj AuthenticateMobileServer:self action:#selector(Handler:)];
return authenticate_G_Obj;
}
-(void)Handler:(id)value
{
authenticate_G_Obj = (AuthenticateObj*)value;
}
Now once the authenticateMobileUser method of classB returns the controll back to ClassA, we will get the Object authenticate_Obj initiated.
My problem is , when i run the project the authenticate_Obj is NULL... actually when it enters the handler method , the Object is initiallized. but the controlled is returned back to ClassA, without entering into Handler method. I guess this is the problem of Asynchronous execution.
How to make it enter into handler method and then only return the controll to ClassA??
Plz help me..
Thank You.
It sounds like what you think you want to do is to block execution until authentication completes. This might be possible if AuthenticateMobileServer spawns a background thread to work in -- you'd use a synchronisation object such as NSLock -- but it's really a Bad Idea. Why have a background thread at all if you're going to block anyway? And thread synchronisation is notoriously tricky and prone to errors if you don't know what you're doing, which (let's face it) you don't.
Instead, you probably should accept that there will be a period of uncertainty while the authentication takes place, during which your app should keep processing in some intermediate state, and then use a callback to notify you when the authentication is complete and you can then go on with whatever it is you need to do with the authenticated user.
There are a bunch of ways you could do this, and there's not enough detail in the question to say exactly which would be best. But you already seem to be using something very similar within ClassB, so I'd say do the same from ClassA:
Inside ClassA:
-(void)authenticateUser
{
authenticate_Obj = nil;
[classB_Obj authenticateMobileUserAndNotify:self action:#selector(authenticatedObject:)];
// returns more or less immediately, not yet authenticated
}
-(void)authenticatedObject:(YourAuthObjectClass*) authObj
{
authenticate_Obj = authObj;
// do post-authentication stuff here
}
Inside ClassB:
-(void)authenticateMobileUserAndNotify:(id)target action:(SEL)sel
{
// I'm making these ivars for simplicity, there might be other considerations though
callbackTarget = target;
callbackSelector = sel;
[mobile_Obj AuthenticateMobileServer:self action:#selector(Handler:)];
}
-(void)Handler:(id)value
{
authenticate_G_Obj = (AuthenticateObj*)value;
[callbackTarget performSelectorOnMainThread:callbackSelector withObject:authenticate_G_Obj waitUntilDone:NO];
}
Obviously this is just a sketch and not intended to be used as is. And you'll need to consider what goes on in your app while in the waiting state, with authentication in progress but authenticate_Obj still nil. But hopefully you get the idea.
I think you are saying that AuthenticateMobileServer:action: is asynchronous and you want to block until it's finished so you can get the return value. Unfortunately, we can't really tell you without knowing how it works. The main question is does it run the Handler action on the main thread or a secondary thread.
If it runs the action on the main thread, the best strategy is to return immediately from authenticateMobileUser without waiting for the authentication object and disable the UI elements that depend on being authenticated. Then later when you get the authentication object, you should re-enable the UI elements.
If it runs the action on a background thread, the easiest thing is to set up another method similar to Handler (by the way, the naming convention for methods and variables is to start with lower case), which you then invoke from Handler with performSelectorOnMainThread:waitUntilDone:. You can then use the same strategy as outlined above.
Both answers of JeremyP and walkytalky are correct and go at the heart of creating a respondsive UI. The rule of thumb:
If you doing potentially blocking operations such as networking on the main thread, you will get in trouble.
There are at least two reasons:
you are blocking the run loop so it cannot process user events anymore. This will result in a spinning beachball on the mac and a unresponsive UI on both mac and iOS.
If you are on iOS, there is a watchdog going around and checking if your UI is still responding to user events. If you are blocking the UI longer than I think 20s you will be terminated with the error code 0x8badf00d.
So to get this things done which maybe take some time you have to do it on the background thread. As the two answers of JeremyP and walkytalky point out often you get a callback. That is fine but there are in total three ways of messaging:
Delegation
Notifications
Kev-value-observing
All three can be and are used. There are subtle differences between them. One of the most important is that delegation is a 1:1 messaging whereas the other to are a 1:n messaging.
Now that said do not think that you have to use NSThread. Have a look at NSOperation and NSOperationQueue instead. They allow to encapsulate pieces of work in an operation and let them run on a queue in the background. Also if you are using these callbacks with the #selector(methodname:) syntax there is something new: blocks. Often there are equivalent methods which take a block instead of a selector to be executed as a callback.
To finish here is the golden rule:
You may update your model on the background thread, but NEVER update your UI on a background thread.
Check out the WWDC10 videos about these topics. There is a great 2-part talk about networking which explains the concepts in detail.
I'm working on a small application using C++/wxWidgets, where several parts of the GUI need to be updated based on e.g. received UDP datagrams. More specifically, a secondary thread tries to keep a list of available "clients" in the network (which may come and go away) and e.g. corresponding comboboxes in the UI need to be updated to reflect the changes.
The documentation mentions that for this kind of thing EVT_UPDATE_UI would be a good choice. As far as I can understand from the sparse documentation, this event is sent automatically by the system and provides some support for assisted UI change.
However, I'd feel more comfortable using a more direct approach, i.e. where e.g. a window object could register/subscribe to receive notifications (either events or callbacks) upon particular events and another part of the code is sending out these notifications when required. I could do this in C++ using my own code, however I guess if wxWidgets already supports something like that, I should make use of it. However I haven't found anything in that regards.
So, the question is: does wxWidgets support this kind of notification system (or similar alternatives) or would I be best served coding my own?
AFAIK there is nothing directly usable in wxWidgets, but doing it on your own seems easy.
What I would do:
Create a wxEvtHandler-descendent class to hold the list of available "clients" in the network. Let this class have a wxCriticalSection, and use a wxCriticalSectionLocker for that in all methods that add or delete "clients".
Create a worker thread class by inheriting wxThread to handle your UDP datagrams, using blocking calls. The thread should directly call methods of the client list object whenever a client has to be added or removed. In these methods update the list of clients, and ::wxPostEvent() an event to itself (this will execute the whole notification calls in the main GUI thread).
Handle the event in the client list class, and notify all listeners that the list of clients has changed. The observer pattern seems to me a good fit. You could either call a method of all registered listeners directly, or send a wxCommandEvent to them.
Have you tried calling Update() on the widget(s) that change? Once you update the contents of the combo box, call Update(), and the contents should update.