I try to put g_timeout_add () on hold in if it meets one condition without being removed with g_source_remove ().
Basically pause/resume thread.
From documentation g_timeout_add () I do not realize how this could be achieved
Now can do this with:
void
schedule_popup (gpointer data)
{
unschedule_popup (data);
timeout_id = g_timeout_add_seconds (POPUP_TIMEOUT, (GSourceFunc) hide_popup_timeout_cb, data);
g_source_set_name_by_id (timeout_id, "[myapp] hide_popup_timeout_cb");
}
void
unschedule_popup (gpointer data)
{
if (timeout_id > 0)
g_source_remove (timeout_id);
timeout_id = 0;
}
Related
is there anything like onCancel for a StreamSubscription?
example:
var subscription = someStream.listen((item) => null);
subscription.cancel(); // does this trigger any event?
I ended up creating a _StreamSubscriptionDelegate that delegates all methods and so I can put some logic when the subscription is cancelled, however, maybe there is an easier solution to it.
If the stream comes from a StreamController, then the controller is notified of the cancel. The listener is expected to keep track of their own subscription, so if one part of the client code needs to know that another part has cancelled the stream, then wrapping the subscription in something which records that you cancelled it, is a perfectly good approach.
Another approach could be to wrap the stream before listening to it:
Stream<T> onCancel<T>(Stream<T> source, void onCancel()) async* {
bool isCancelled = true;
try {
await for (var event in source) {
yield event; // exits if cancelled.
}
isCancelled = false;
} finally {
if (isCancelled) onCancel();
}
}
or
Stream<T> onCancel<T>(Stream<T> source, void onCancel()) {
var sink = StreamController<T>();
sink.onListen = () {
var subscription = source.listen(sink.add, onError: sink.onError, onDone: sink.close);
sink
..onPause = subscription.pause
..onResume = subscription.resume
..onCancel = () {
subscription.cancel();
onCancel();
};
};
return sink.stream;
}
I have the following code for my IOS implementation, the problem is that the WroteCharacteristicValue event is never fired. Is is being fired on the android side when I connect to the same module. Any ideas what to do?
public void StartUpdates ()
{
// TODO: should be bool RequestValue? compare iOS API for commonality
bool successful = false;
if(CanRead) {
Console.WriteLine ("** Characteristic.RequestValue, PropertyType = Read, requesting read");
_parentDevice.UpdatedCharacterteristicValue += UpdatedRead;
_parentDevice.ReadValue (_nativeCharacteristic);
successful = true;
}
if (CanUpdate) {
Console.WriteLine ("** Characteristic.RequestValue, PropertyType = Notify, requesting updates");
_parentDevice.UpdatedCharacterteristicValue += UpdatedNotify;
_parentDevice.WroteCharacteristicValue += Wrote; // -DP here??
_parentDevice.SetNotifyValue (true, _nativeCharacteristic);
successful = true;
}
Console.WriteLine ("** RequestValue, Succesful: " + successful.ToString());
}
void Wrote(object sender, CBCharacteristicEventArgs e) {
System.Diagnostics.Debug.WriteLine("Characteristic Write Complete!");
this.WriteComplete (this, new CharacteristicReadEventArgs () {
Characteristic = new Characteristic(e.Characteristic, _parentDevice)
});
}
The WroteCharacteristic will only fire if the characteristic writes with response.
You can check it with:
var prop = _nativeCharacteristic.Properties;
if(prop.HasFlag(CBCharacteristicProperties.Write))
{
// Event can be used
}
else if(prop.HasFlag(CBCharacteristicProperties.WriteWithoutResponse))
{
// Event will not fire if WriteWithoutResponse
}
Btw: we provide a plugin for BLE, so you don't have to care about platform sepcific stuff ;) http://smstuebe.de/2016/05/13/blev1.0/
This is related to is there any way to cancel a dart Future?
In my case, there are no HTTP, just expensive calculations. I have a table/list which I scroll through. As the elements become visible, I generate futures to show the calculation results. But if I (the end user) scroll quickly, some results will have "scrolled out of view" and will no longer required. This could be a large number, and would seriously delay the return of futures (results) that are to be usefully :-) displayed in currently visible elements. Can something be done about that? cheers, Steve
You could just set a flag which indicates to the delayed code (run from futures) that the result isn't needed anymore.
When the delayed code is called it just returns.
library cancel_future;
import 'dart:async' show Future, Timer;
import 'dart:math' show Random;
typedef void TaskFunction(Task task);
// Container for a task
class Task {
// an assigned task id
final id;
// data to process
int data;
// Indicate to the task function, that it should stop processing
bool isCanceled = false;
// The task function must set this flat to true when all work is done.
bool isFinished = false;
// The task function which processed the data and sets the result.
TaskFunction fn;
// The result set by the task function when it finished processing.
int result;
Task(this.id, this.data, this.fn);
// Start processing the task.
void execute() => fn(this);
}
final rnd = new Random();
void main(List<String> args) {
// create tasks
final tasks = new List<Task>.from(generate());
// start all tasks
tasks.forEach((t) => t.execute());
// after random delay cancel all unfinished tasks
new Future.delayed(new Duration(seconds: rnd.nextInt(10)), () {
tasks.forEach((t) {
if (!t.isFinished) {
t.isCanceled = true;
}
});
}).then((_) {
// check results
int done = 0;
int canceled = 0;
tasks.forEach((t) {
print(
'Task id: ${t.id}; isCanceled: ${t.isCanceled}; isFinished: ${t.isFinished}; data: ${t.data}; result: ${t.result}');
if (t.isFinished) {
done++;
}
if (t.isCanceled) {
canceled++;
}
});
print('Canceled: $canceled.');
print('Done: $done.');
});
}
// geneator for job 100 jobs
Iterable<Task> generate() sync* {
int i = 0;
while (i++ < 100) {
yield new Task(i, rnd.nextInt(100), calc);
}
}
// job function
void calc(Task t) {
// do a bit of work every 100ms to simulate longer processing
new Timer.periodic(new Duration(milliseconds: 100), (timer) {
var result = 0;
// check if jost was canceled and stop processing in case it was.
if (t.isCanceled) {
timer.cancel();
return;
}
// while not finished do a chunk of work
if (result < t.data) {
result++;
} else {
// finished - clean up and store result
t.isFinished = true;
t.result = result;
timer.cancel();
}
});
}
I am trying to use dart isolate library to improve my application performance.
Look at following code:
import 'dart:isolate';
import 'package:dbcrypt/dbcrypt.dart';
main() {
var pwConPort = new ReceivePort();
pwConPort.listen((data) {
print(data);
pwConPort.close();
}, onError: (err) {
print(err);
});
Isolate.spawn(generatePasswordConcurrency, pwConPort.sendPort);
}
void generatePasswordConcurrency(SendPort sendPort) {
sendPort.send(_generateHashPassword('Passsowr1222!'));
}
String _generateHashPassword(String password) {
var regex = new RegExp(r'^.*(?=.{7,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[^a-zA-Z0-9]).*$');
if (!regex.hasMatch(password)) {
throw new StateError('Errors');
}
return new DBCrypt().hashpw(password, new DBCrypt().gensalt());
}
Everything works fine but i can only pass a static password, or better to say, i don't know, how to pass something dynamically. Here you can see, password is hardcoded, but i want to pass a variable for example.
void generatePasswordConcurrency(SendPort sendPort) {
sendPort.send(_generateHashPassword('Passsowr1222!'));
}
If the method _generateHashPassword will throw an error, how can I handling this error? I try to catch the error on listen method from ReceivePort
pwConPort.listen((data) {
print(data);
pwConPort.close();
}, onError: (err) {
print(err);
});
but still got unhandling exceptions message.
Observatory listening on http://127.0.0.1:51433
in ShutdownIsolate: Unhandled exception:
Bad state: Errors
#0 _generateHashPassword (file:///D:/Dart/samples/bin/isolate_error.dart:26:9)
#1 generatePasswordConcurrency (file:///D:/Dart/samples/bin/isolate_error.dart:19:40)
#2 _startIsolate.isolateStartHandler (dart:isolate-patch/isolate_patch.dart:221)
#3 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:124)
Conclusion my question:
How can I pass a variable to called method on isolate?
How can I handling error on isolate?
First of all,
Isolate are not thread, they are independant process more like a fork() than a thread
dartApi: Isolate
Concurrent programming using isolates:
independent workers that are similar to threads but don't share memory, communicating only via
messages.
So, you can't access to the same variable than your parent process. It's a choice made by the dart team, because it's a mechanism usable when you compile your dart code in js. So it need to be possible in JS
How can I pass a variable to called method on isolate?
To do this, you need to see ReceivePort() like a unidirectionnal way of communication, so to pass variable in two way, you need two.
So on you main process:
pwConPort.listen((data) {
if (isolateSendPort == null && data is SendPort) {
isolateSendPort = data; // Receive the communication object of the isolate
isolateSendPort.send("Passsowr1222!");
} else {
print("Generated password: ${data}");
pwConPort.close();
}
}, onError: (err) {
print("SendPortError: ${err}");
});
});
In you isolate entry point :
sendPort.send(isolateConPort.sendPort);
isolateConPort.listen((data) {
// code ....
});
Note: be careful of what message you send. message send between one process and another need to respect some rules
DartApi: SendPort
The content of message can be: primitive values (null, num, bool,
double, String), instances of SendPort, and lists and maps whose
elements are any of these. List and maps are also allowed to be
cyclic.
How can I handling error on isolate?
Isolate get one method to listen throw error send by the isolate : addErrorListner
That is a useful function.
BUT ! this method is not implement in every plate-forme, so you need to do this in a others.
The way i chose is to send 2 SendPort in the entry point function :
One for the communication
One for the error.
So the spawn function looks like :
Isolate.spawn(generatePasswordConcurrency, [pwConPort.sendPort, errorPort.sendPort])
and the generatePasswordConcurrency :
void generatePasswordConcurrency(List<SendPort> commList) {
var sendPort = commList[0];
var errorPort = commList[1];
var isolateConPort = new ReceivePort();
sendPort.send(isolateConPort.sendPort);
isolateConPort.listen((data) {
try {
sendPort.send(_generateHashPassword(data));
} catch (e) {
errorPort.send("error: ${e.toString()}");
}
});
}
Here the full code :
import 'dart:isolate';
import 'package:dbcrypt/dbcrypt.dart';
main() {
var pwConPort = new ReceivePort();
var errorPort = new ReceivePort();
SendPort isolateSendPort = null;
Isolate.spawn(generatePasswordConcurrency, [pwConPort.sendPort, errorPort.sendPort])
.then((Isolate pcs) {
errorPort.listen((err) {
print("Error: ${err}");
pwConPort.close();
errorPort.close();
});
print(pcs);
pwConPort.listen((data) {
if (isolateSendPort == null && data is SendPort) {
isolateSendPort = data;
isolateSendPort.send("Passsowr1222!");
} else {
print("Generated password: ${data}");
pwConPort.close();
errorPort.close();
//pcs.kill();
}
}, onError: (err) {
print("SendPortError: ${err}");
});
});
}
void generatePasswordConcurrency(List<SendPort> commList) {
var sendPort = commList[0];
var errorPort = commList[1];
var isolateConPort = new ReceivePort();
sendPort.send(isolateConPort.sendPort);
isolateConPort.listen((data) {
try {
sendPort.send(_generateHashPassword(data));
} catch (e) {
errorPort.send("error: ${e.toString()}");
}
});
}
String _generateHashPassword(String password) {
var regex = new RegExp(r'^.*(?=.{7,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[^a-zA-Z0-9]).*$');
if (!regex.hasMatch(password)) {
throw new StateError('Errors');
}
return new DBCrypt().hashpw(password, new DBCrypt().gensalt());
}
I launch a request to a server with a future "requestServer".
I would like to poll a system for a specific value (passed from false to true, when request is done) and return when finished.
Code could be like that, but "while" synchronous and "checkOperation" is asynchronous?
return requestServer().then((operation) {
var done = false;
while (done)
return checkOperation(operation).then((result) {
done = (result == true);
});
sleep(10);
}
});
Any ideas ?
I guess this is not exactly what you want but as far as I know there is no way to block execution so you have to use callbacks.
void main(List<String> args) {
// polling
new Timer.periodic(new Duration(microseconds: 100), (t) {
if(isDone) {
t.cancel();
someCallback();
}
});
// set isDone to true sometimes in the future
new Future.delayed(new Duration(seconds: 10), () => isDone = true);
}
bool isDone = false;
void someCallback() {
print('isDone: $isDone');
// continue processing
}
You can of course pass the callback as parameter instead of hardcode it, because functions are first class members in Dart.
Polling doesn't work very well for async. It is better to wait for a signal from the thing that must complete.
Günter Zöchbauer's answer shows you how to poll anyway, by sampling with a timer.
As an alternative, it would be better to not have a boolean done, but instead complete another future when you are ready. This is busy-polling, which polls again as soon as a result comes back, which may be more intensive than you need. Using timer based polling can be more efficient if you don't need the result as soon as possible.
return requestServer().then((operation) {
var completer = new Completer();
void poll(result) {
if (!result) {
operation.then(poll, onError: completer.completeError);
} else {
completer.complete();
}
}
poll(false);
return completer.future;
});
(Code not really tested, since I don't have your requestServer).
When you want build functions that return Futures, it is sometimes useful to use Completers. Think that requestServer() is living in the Future too, so you will have threat the result as a Future.
return requestServer().then((operation) {
// This is necessary then you want to control async
// funcions.
Completer completer = new Completer();
//
new Timer.periodic(const Duration(seconds: 10), (_) {
checkOperation(operation).then((result) {
// Only when the result is true, you pass the signal
// that the operation has finished.
// You can alse use `completer.complete(result)` if you want
// to pass data inside of the future.
if (result == true) completer.complete();
});
});
// You return the future straight away.
// It will be returned by requestServer();
return completer.future;
});
I use a function like this in a TestUtil library:
static Future<bool> waitUntilTrue(bool Function() callback,
{Duration timeout: const Duration(seconds: 2),
Duration pollInterval: const Duration(milliseconds: 50)}) {
var completer = new Completer<bool>();
var started = DateTime.now();
poll() {
var now = DateTime.now();
if (now.difference(started) >= timeout) {
completer.completeError(Exception('timed out in waitUntilTrue'));
return;
}
if (callback()) {
completer.complete(true);
} else {
new Timer(Duration(milliseconds: 100), () {
poll();
});
}
}
poll();
return completer.future;
}
And then in my test code I'll do something like:
await TestUtil.waitUntilTrue(() => someObj.isDone);
Edit:
Note that if you're using this in a testWidgets test, you have to do a little extra, since it relies on real async work happening:
await tester.runAsync<bool>(
() => TestUtil.waitUntilTrue(() => myObj.isLoaded),
additionalTime: Duration(seconds: 5));