I want create timer in my program so that I can cause it to rerun every minute and I don't know how to do it in a C++ Application. In C# I could just create a timer but I'm struggling here now...
sleep(); is not an option because as far as I know it makes your program inactive for X seconds, I need my app to be active and working, calculating all the time. This is because my code is used to constantly input information into a MS Access table. I was able to create the necessary components of my code to connect and perform the insert/update to the table but this is just on of the many components to the code that I am creating. Please help me with this little (or big?) problem, I'm very new to C++ and learning ATM, but I am developing a fast learning curve. Thanks
I suppose you work on Windows, since you mentioned C#. So take a look at SetTimer, and if it is a MFC app, then look at CWnd::SetTimer.
Every platform provides api for creating a timer, which will give you a callback usually after timer expires. You can just search for the api available on your platform.
If you are using windows use setTimer function.
If you're using C++ .NET, you can use the same Timer class(es) as C#, just use the C++ syntax (using gcnew instead of new, use the ^ for GC references).
Otherwise you could just have a loop:
while (should_keep_looping) {
// do what you need to do
// if necessary:
sleep(1);
}
See here: http://www.cplusplus.com/forum/beginner/317/
There is on built in "timer" in C++, and you are correct about the behavior of sleep(). The above thread describes a custom implementation.
if you have a window you can use its message queue, as suggested by Als and Marius in their answers
you can use some task dispatcher and some timer to register a callback, e.g. functionality provided by Boost.Asio and its deadline_timer (example)
you can check if timer expired between your tasks manually as proposed in BlackJack's link
or you can create separate thread and make it call your callback when time came. Pros: you can use sleep() there and you callback will be called in parallel with your main thread. Cons: worry about synchronization
Related
I'm trying to create a node interface for a c++ media player. Upon decoding of a frame, there is an event which allows me to access the frame data, which I'm trying to funnel into node. But I can't seem to figure out how to get that kind of functionality to work with the functions available in the node api. My approach, for the time being, is to figure out a push mechanism to get the data from c++ to javascript where all i need is to initialize a callback in javascript, since it seems more elegant. If that fails I could create a polling loop in js to check if there is new frame data, but it seems less efficient.
I've tried with napi_create_async_work, by creating a lambda function in the execute parameter function, which would allow me to call napi_make_callback for every frame callback, but then I get the following error :
Fatal error in HandleScope::HandleScope
Entering the V8 API without proper locking in place
I'm likely approaching this incorrectly, its the first time I use n-api.
Any help is welcome, thank you!
The issue is mainly pertaining to the fact you can’t access V8 (JavaScript) memory outside the event-loop’s main thread. If you're creating an async thread, by default you're also creating a new memory stack.
Fortunately, a fix is on the way which should allow thread safe access with
napi_create_threadsafe_function (example here)
Until then
There is a header only C++ package which integrates great with the C++ N-API wrapper
Napi-addon-api is update. These is a good way that use the Napi::ThreadSafeFunction.
Doc and example.
In objective C there is a method called performselector which help developer to run a method after a time.
https://developer.apple.com/reference/objectivec/nsobject/1416176-performselector
I need a similar logic in C++. I am working with winapi.
I could not implement CreateTheread and WaitForSingleObjectEx since my method is not static.
Is there similar approach in C++ like performselector?
Use a timer from Win API: (edited, thanks to #user2120666)
If you use a GUI (which relies on user32 lib):
https://msdn.microsoft.com/en-us/library/windows/desktop/ms644906(v=vs.85).aspx
If your app is of console-only-type (just kernel32 lib):
https://msdn.microsoft.com/en-us/library/ms686796.aspx
And handle its message. Do all of it in the main thread. This is how Apple does:
This method sets up a timer to perform the aSelector message on the
current thread’s run loop.
use mfc and override CWinApp::OnIdle function.
Could there be any reason why sendARAnimationObject should stop working without any change in the code? Does rendering of bitmaps in a timer depend on any external state like battery level or sensor state etc?
Another issue is that if I use sendARAnimationObjectWithCallback the callback method in the listener onResultSendAnimationObject is never called as stated in the documentation. Could there be any other dependency causing this callback method not called at all?
It works much better with the official SDK v1.0
Now I belive I found the main reason behind. I was not calling disableARAnimationRequest anywhere in my app. Now I am calling it in onPause and it works much better next time I start the app and call enableARAnimationRequest. But I would need someone at sony to confirm this kind of behaviour. Maybe the disable method should be called in some SDK method without putting that burden on the developer. Or some kind of cleanup in SDK when you start your app and enable animation request.
I have some native code and want to update the progressbar from the native code. There isn't no return value because it is a long duration task.
I found a small example http://developer.android.com/reference/android/widget/ProgressBar.html but when I move the update part in a extra method I get a NullPointerException.
It seems that this part must be in the thread of the progressbar.
I tried another way by using the AsyncTask as nested class, but I haven't access on the method publishProgress from anywhere outside the class itself.
Is there any possibility to get it working?
If it is possible to break your long task into multiple incremental calls then I'd recommend doing that. Then you can make those calls from a loop inside AsyncTask.doInBackground(), just like in the SDK examples.
If that's not possible, you'll need a progress variable in your native code that can safely be accessed from multiple threads: Write to it from your worker code and read it from a new "getProgress()" JNI function, with the appropriate synchronisation done in native code. You would then be able to call your getProgress() function from AsyncTask.doInBackground(), or whatever UI scheme you choose to use.
What's the approved way to handle second, third, etc launches of application in Windows (C++) application? I need the running (first) instance to take some special action (pop up a dialog) in this case, but for the secondary instances to terminate.
On Mac, AppleEvents sends you a 're-open' message in this scenario. Mozilla on Windows uses DDE to check for an existing instance and pass the command line through. It feels like a pretty nasty solution, all the same.
The windows way is to open a named mutex and, if you can acquire it, it means you're the first instance, if not, there is another one. At this point you can register a windows message (the function is literally RegisterWindowsMessage) which gives you a WM_ msg you can send to all windows and only your app would know to catch it, which allows you to tell your initial copy to open a dialog box or w/e.
How to limit 32-bit applications to one instance in Visual C++
"The method that is used in this article is the one that is described in MSDN under the WinMain topic. It uses the CreateMutex function to create a named mutex that can be checked across processes. Instead of duplicating the same code for every application that you will use as a single instance, the code that you must have is in a C++ wrapper class that you can reuse across each application."
SendMessage Function
"Sends the specified message to a window or windows. The SendMessage function calls the window procedure for the specified window and does not return until the window procedure has processed the message."
"Applications that need to communicate using HWND_BROADCAST should use the RegisterWindowMessage function to obtain a unique message for inter-application communication."
RegisterWindowMessage
"The RegisterWindowMessage function defines a new window message that is guaranteed to be unique throughout the system. The message value can be used when sending or posting messages."
On windows there is not really solution for that at least not out of the box.
You can use mutex to do such things, basically the app check for the mutex at startup create it if it doesn't exist.
There is one issue with CreateMutex method that you might need to consider - the named mutex might have been created by a third party. Now, most of the time, this won't be an issue, there would be no reason for someone else to block your application. However, if you're making a program that does something important, it may be an issue. Consider, if your program was a virus scanner, a virus could disable it by creating the mutex.
Usually, CreateMutex should do the job, but you should be aware of the limits of this method.