mattleibow
commented
1 year ago Although having perfect page synchronization, I also think that the lifetime of a service that needs clean shutdown should not be on the page.
One thing that may happen is the device can be backgrounded at any time - or the user could rotate the device and trigger a full page reconstruction (in some cases).
It may be better to have a singleton service that is independent of the page and rather the page requests the scanner or requests a shutdown. Below I have totally pseudo-coded an idea, but may form some starting/searching point. In this case, you do not want to attach the scanner to the page, but rather let the scanner work at its own pace and you wait for events/tasks. An alternate (and probably simpler) implementation is to use events so that all things can access the scanner without having to create/destroy on every page navigation. You could have a buffer so if the user accidentally taps a different page/tab, you don't shutdown immediately.
class ScannerService
{
object _locker = new();
TheScannerThing? _scanner;
TaskCompletionSource<TheScannerThing?> _tcs;
TaskCompletionSource _tcsShutdown;
public Task<TheScannerThing?> RequestStartup() {
lock (_locker) {
// wait for any previous shutdowns to happen
if (_tcsShutdown is not null) {
await _tcsShutdown.Task;
_tcsShutdown = null;
}
// return current request
if (_tcs is not null)
return _tcs.Task;
// start a new one
_tcs = new();
if (_scanner is null) {
_scanner = CreateScannerInstance();
_scanner.OnReady += {
// the scanner is ready, so return all the tasks
_tcs.TrySetResult(_scanner);
};
_scanner.OnError += {
_tcs.TrySetException(...);
};
_scanner.Start();
}
}
}
public Task RequestShutdown() {
lock (_locker) {
// wait for any startups to complete
// start shutdown
}
}
}
ghost
genifycom
Description
A classic example of this is using a resource like a Scanner (in SPP mode). On Page A, the scanner is initialized and connected. On a page switch, the scanner needs to be cleanly shutdown (serial port closed and reset). On the switch to another (or the same page), the scanner needs to be in a state that it can be reconnected.
The page dispose does not guarantee that Page A dispose is complete before the next page starts its process but the resource (could be a database, scanner, other device) access needs to be serialized.
How do we handle this using Blazor pages? Is there a way to synchronize cleanly the cleanup of one page before starting up another (not every time of course, but when needed).
Thanks
Public API Changes
Synchronization object that a page might use to coordinate page changes.
Intended Use-Case
For use with page resources that require synchronization for initialize and shutdown.