I am writing code to consume WinRT API on Windows 10 using C++ WRL (i.e. without using either C++/CX or C++/CLI). I am using GetAppListEntriesAsync() from Package class to get names of UWP applications installed on a system. GetAppListEntriesAsync() calls a callback method asynchronously. I want to wait till all such asynchronous methods have finished. Unlike C++/CX WRL doesn't have any await keyword to wait on asynchronous tasks.
Details
The following code is used to get the list.
ComPtr<ABI::Windows::Foundation::__FIAsyncOperation_1___FIVectorView_1_Windows__CApplicationModel__CCore__CAppListEntry_t> operation;
package3->GetAppListEntriesAsync(&operation);
package3 is pointer to type ABI::Windows::ApplicationModel::IPackage3:-
ComPtr<ABI::Windows::ApplicationModel::IPackage3> package3;
I invoke the asynchronous operation as follows.
operation->put_Completed(cb.Get())
Where cb holds reference to callback function that GetAppListEntriesAsync() calls asynchronously. (see update2)
There are several such asynchronous operations which are invoked. I want to run a piece of code which should run only after all such asynchronous callbacks have completed. C++/CX has await keyword for doing a wait on asynchronous tasks.
How should I do the same using WRL C++?
I tried using WaitForSingleObject() but it doesn't seem to work.
A very brute approach would be to keep checking status of every asynchronous operation in a while loop.
ComPtr<ABI::Windows::Foundation::IAsyncInfo> ai;
operation.As(&ai);
while (true)
{
ai->get_Status(&status);
if (status == Started)
{
continue;
}
else
{
break;
}
}
I am not sure if this is guaranteed to work, or whether if it will incur performance penalty. The COM apartment type for my code is APTTYPE_STA (note sure if this piece of information is relevant to the question; I wanted to set is to RO_INIT_MULTITHREADED but RoInitialize() fails, however WRL code seems to be working fine).
UPDATE 2:
Here is how cb (callback) is implemented.
auto cb = wrl::Callback<ABI::Windows::Foundation::IAsyncOperationCompletedHandler<ABI::Windows::Foundation::Collections::__FIVectorView_1_Windows__CApplicationModel__CCore__CAppListEntry_t *>>(
[](ABI::Windows::Foundation::__FIAsyncOperation_1___FIVectorView_1_Windows__CApplicationModel__CCore__CAppListEntry_t * ppp, AsyncStatus status) -> HRESULT
{
<do something in callback>;
SetEvent(threadCompleted.Get());
}
Trying to implement IAgileObject.
To make my callback implement IAgileObject I will have to use Implements<> WRL template class. so callback would be something like auto cb = Callback<Implements<IAgileObject,...>> but the problem is that IAsyncOperationCompletedHandler<ABI::Windows::Foundation::Collections::__FIVectorView_1_Windows__CApplicationModel__CCore__CAppListEntry_t *> doesn't derive from IInspectable, hence using Implements on that :-
Callback<Implements<ABI::Windows::Foundation::IAsyncOperationCompletedHandler<ABI::Windows::Foundation::Collections::__FIVectorView_1_Windows__CApplicationModel__CCore__CAppListEntry_t *>,IAgileObject>> gives the following error (Visual Studio 2017).
Error C2338 'I' has to derive from 'IWeakReference', 'IWeakReferenceSource' or 'IInspectable' AsyncTask c:\sw\tools\sdk\winsdk\win10\include\winrt\wrl\implements.h 413
Related
Background
I have a legacy application where I need to return a List<Item>
There are many different Service classes each belonging to an ItemType.
Each service class calls a few different backend APIs and collects the responses to create a SubType of the Item.
So we can say, each service class implementation returns an Item
All backend API access code is using WebClient which returns Mono of some type, and I can zip all Mono within the service to create an Item
The user should be able to look up many different types of items in one call. This requires many backend calls
So for performance sake, I wanted to make this all asynchronous using reactor, so I introduced Spring Reactive code.
Problem
If my endpoint had to return Flux<Item> then this code work fine,
But this is some service code which is used by other legacy code caller.
So eventually I want to return the List<Item> but When I try to convert my Flux into the List I get an error
"message": "block()/blockFirst()/blockLast() are blocking,
which is not supported in thread reactor-http-nio-3",
Here is the service, which is calling a few other service classes.
Flux<Item> itemFlux = Flux.fromIterable(searchRequestByItemType.entrySet())
.flatMap(e ->
getService(e.getKey()).searchItems(e.getValue()))
.subscribeOn(Schedulers.boundedElastic());
Mono<List<Item>> listMono = itemFlux
.collectList()
.block(); //This line throws error
Here is what the above service is calling
default Flux<Item> searchItems(List<SingleItemSearchRequest> requests) {
return Flux.fromIterable(requests)
.flatMap(this::searchItem)
.subscribeOn(Schedulers.boundedElastic());
}
Here is what a single-item search is which is used by above
public Mono<Item> searchItem(SingleItemSearchRequest sisr) {
return Mono.zip(backendApi.getItemANameApi(sisr.getItemIdentifiers().getItemId()),
sisr.isAddXXXDetails()
?backendApi.getItemAXXXApi(sisr.getItemIdentifiers().getItemId())
:Mono.empty(),
sisr.isAddYYYDetails()
?backendApi.getItemAYYYApi(sisr.getItemIdentifiers().getItemId())
:Mono.empty())
.map(tuple3 -> Item.builder()
.name(tuple3.getT1())
.xxxDetails(tuple3.getT2())
.yyyDetails(tuple3.getT3())
.build()
);
}
Sample project to replicate the problem..
https://github.com/mps-learning/spring-reactive-example
I’m new to spring reactor, feel free to pinpoint ALL errors in the code.
UPDATE
As per Patrick Hooijer Bonus suggestion, updating the Mono.zip entries to always contain some default.
#Override
public Mono<Item> searchItem(SingleItemSearchRequest sisr) {
System.out.println("\t\tInside " + supportedItem() + " searchItem with thread " + Thread.currentThread().toString());
//TODO: how to make these XXX YYY calls conditionals In clear way?
return Mono.zip(getNameDetails(sisr).defaultIfEmpty("Default Name"),
getXXXDetails(sisr).defaultIfEmpty("Default XXX Details"),
getYYYDetails(sisr).defaultIfEmpty("Default YYY Details"))
.map(tuple3 -> Item.builder()
.name(tuple3.getT1())
.xxxDetails(tuple3.getT2())
.yyyDetails(tuple3.getT3())
.build()
);
}
private Mono<String> getNameDetails(SingleItemSearchRequest sisr) {
return mockBackendApi.getItemCNameApi(sisr.getItemIdentifiers().getItemId());
}
private Mono<String> getYYYDetails(SingleItemSearchRequest sisr) {
return sisr.isAddYYYDetails()
? mockBackendApi.getItemCYYYApi(sisr.getItemIdentifiers().getItemId())
: Mono.empty();
}
private Mono<String> getXXXDetails(SingleItemSearchRequest sisr) {
return sisr.isAddXXXDetails()
? mockBackendApi.getItemCXXXApi(sisr.getItemIdentifiers().getItemId())
: Mono.empty();
}
Edit: Below answer does not solve the issue, but it contains useful information about Thread switching. It does not work because .block() is no problem for non-blocking Schedulers if it's used to switch to synchronous code.
This is because the block operator inherited the reactor-http-nio-3 Thread from backendApi.getItemANameApi (or one of the other calls in Mono.zip), which is non-blocking.
Most operators continue working on the Thread on which the previous operator executed, this is because the Thread is linked to the emitted item. There are two groups of operators where the Thread of the output item differs from the input:
flatMap, concatMap, zip, etc: Operators that emit items from other Publishers will keep the Thread link they received from this inner Publisher, not from the input.
Time based operators like delayElements, interval, buffer(Duration), etc. will schedule their tasks on the provided Scheduler, or Schedulers.parallel() if none provided. The emitted items will then be linked to the Thread the task was scheduled on.
In your case, Mono.zip emits items from backendApi.getItemANameApi linked to reactor-http-nio-3, which gets propagated downstream, goes outside both the flatMap in searchItems and in itemFlux, until it reaches your block operator.
You can solve this by placing a .publishOn(Schedulers.boundedElastic()), either in searchItem, searchItems or itemFlux. This will cause the item to switch to a Thread in the provided Scheduler.
Bonus: Since you requested to pinpoint errors: Your Mono.zip will not work if sisr.isAddXXXDetails() is false, as Mono.zip discards any element it could not zip. Since you return a Mono.empty() in that case, no items can be zipped and it will return an empty Mono.
If we have only spring-boot-starter-webflux defined as application dependency, then springbok spin up a `Netty server.
One is not expected to block() in a reactive application using a non-blocking server.
However, once we add spring-boot-starter-web dependency then even with the presence of spring-boot-starter-webflux, springboot spinup a tomcat server. Which is a thread-per-request model and is expected to have blocking calls
So to solve my problem, all I had to do above is, to add spring-boot-starter-web dependency in pom.xml. After that applications is started in Tomcat
with timcat .collectList().block() works in Controller class to return the List<Item>.
Whereas with the Netty server I could return only Flux<Item> not List<Item>, which is expected.
I am attempting to put together a Cro service that has a react/whenever block consuming data "in the background" So unlike many examples of websocket usage with Cro, this has nothing to do with routes that may be accessed via the browser.
My use case is to consume message received via an MQTT topic and do some processing with them. At a later stage in development I might create a supply out of this data, but for now, when data is received it will be stored in a variable and dependant on certain conditions, be sent to another service via a http post.
My thought was to include a provider() in the Cro::HTTP::Server setup like so:
use Cro::HTTP::Log::File;
use Cro::HTTP::Server;
use Routes;
use DataProvider; # Here
my Cro::Service $http = Cro::HTTP::Server.new(
http => <1.1>,
host => ...,
port => ...,
application => [routes(), provider()], # Made this into an array of subs?
after => [
Cro::HTTP::Log::File.new(logs => $*OUT, errors => $*ERR)
]
);
And in the DataProvider.pm6:
use MQTT::Client;
sub provider() is export {
my $mqtt = MQTT::Client.new: server => 'localhost';
react {
whenever $mqtt.subscribe('some/mqtt/topic') {
say "+ topic: { .<topic> } => { .<message>.decode("utf8-c8") }";
}
}
}
This throws a bunch of errors:
A react block:
in sub provider at DataProvider.pm6 (DataProvider) line 5
in block <unit> at service.p6 line 26
Died because of the exception:
Invocant of method 'write' must be an object instance of type
'IO::Socket::Async', not a type object of type 'IO::Socket::Async'. Did
you forget a '.new'?
in method subscribe at /home/cam/raku/share/perl6/site/sources/42C762836A951A1C11586214B78AD34262EC465F (MQTT::Client) line 133
in sub provider at DataProvider.pm6 (DataProvider) line 6
in block <unit> at service.p6 line 26
To be perfectly honest, I am totally guessing that this is how I would approach the need to subscribe to data in the background of a Cro service, but I was not able to find any information on what might be considered the recommended approach.
Initially I had my react/whenever block in the main service.pm6 file, but that did not seem right. And needed to be wrapped in a start{} block because as I have just learned, react is blocking :) and cro was not able to actually start.
But following the pattern of how Routes are implemented seemed logical, but I am missing something. The error speaks about setting up a new method, but I'm not convinced that is the root cause. Routes.pm6 does not have a constructor.
Can anyone point me in the right direction please?
Thanks to all who have provided information, this has been a very valuable learning exercise.
The approach of passing additional sub routines, along side router() in the application parameter to Cro::HTTP::Server.new gave further trouble. (an array is not allowed, and broke routing)
Instead, I have moved the background work into a class of it's own, and given it a start and stop method more akin to Cro::HTTP::Server.
My new approach:
service.pm6
use Cro::HTTP::Log::File;
use Cro::HTTP::Server;
use Routes;
use KlineDataSubscriber; # Moved mqtt functionality here
use Database;
my $dsn = "host=localhost port=5432 dbname=act user=.. password=..";
my $dbh = Database.new :$dsn;
my $mqtt-host = 'localhost';
my $subscriber = KlineDataSubscriber.new :$mqtt-host;
$subscriber.start; # Inspired by $http.start below
my Cro::Service $http = Cro::HTTP::Server.new(
http => <1.1>,
host => ...,
port => ...,
application => routes($dbh), # Basically back the way it was originally
after => [
Cro::HTTP::Log::File.new(logs => $*OUT, errors => $*ERR)
]
);
$http.start;
say "Listening at...";
react {
whenever signal(SIGINT) {
say "Shutting down...";
$subscriber.stop;
$http.stop;
done;
}
}
And in KlineDataSubscriber.pm6
use MQTT::Client;
class KlineDataSubscriber {
has Str $.mqtt-host is required;
has MQTT::Client $.mqtt = Nil;
submethod TWEAK() {
$!mqtt = MQTT::Client.new: server => $!mqtt-host;
await $!mqtt.connect;
}
method start(Str $topic = 'act/feed/exchange/binance/kline-closed/+/json') {
start {
react {
whenever $!mqtt.subscribe($topic) {
say "+ topic: { .<topic> } => { .<message>.decode("utf8-c8") }";
}
}
}
}
method stop() {
# TODO Figure how to unsubscribe and cleanup nicely
}
}
This feels much more "Cro idiomatic" to me, but I would be happy to be corrected.
More importantly, it works as expected and I feel is somewhat future proof. I should be able to create a supply to make real-time data available to the router, and push data to any connected web clients.
I also intend to have a http GET endpoint /status with various checks to ensure everything healthy
The root cause
The error speaks about setting up a new method, but I'm not convinced that is the root cause.
It's not about setting up a new method. It's about a value that should be defined instead being undefined. That typically means a failure to attempt to initialize it, which typically means a failure to call .new.
Can anyone point me in the right direction please?
Hopefully this question helps.
Finding information on a recommended approach
I am totally guessing that this is how I would approach the need to subscribe to data in the background of a Cro service, but I was not able to find any information on what might be considered the recommended approach.
It might be helpful for you to list which of the get-up-to-speed steps you've followed from Getting started with Cro, including the basics but also the "Learn about" steps at the end.
The error message
A react block:
in sub provider ...
Died because of the exception:
...
in method subscribe ...
The error message begins with the built in react construct reporting that it caught an exception (and handled it by throwing its own exception in response). A "backtrace" corresponding to where the react appeared in your code is provided indented from the initial "A react block:".
The error message continues with the react construct summarizing its own exception (Died because ...) and explains itself by reporting the original exception, further indented, in subsequent lines. This includes another backtrace, this time one corresponding to the original exception, which will likely have occurred on a different thread with a different callstack.
(All of Raku's structured multithreading constructs[1] use this two part error reporting approach for exceptions they catch and handle by throwing another exception.)
The first backtrace indicates the react line:
in sub provider at DataProvider.pm6 (DataProvider) line 5
use MQTT::Client;
sub provider() is export {
my $mqtt = MQTT::Client.new: server => 'localhost';
react {
The second backtrace is about the original exception:
Invocant of method 'write' must be an object instance of type
'IO::Socket::Async', not a type object of type 'IO::Socket::Async'. ...
in method subscribe at ... (MQTT::Client) line 133
This reports that the write method called on line 133 of MQTT::Client requires its invocant is an instance of type 'IO::Socket::Async'. The value it got was of that type but was not an instance, but instead a "type object". (All values of non-native types are either type objects or instances of their type.).
The error message concludes with:
Did you forget a '.new'?
This is a succinct hint based on the reality that 99 times out of a hundred the reason a type object is encountered when an instance is required is that code has failed to initialize a variable. (One of the things type objects are used for is to serve the role of "undefined" in languages like Perl.)
So, can you see why something that should have been an initialized instance of 'IO::Socket::Async' is instead an uninitialized one?
Footnotes
[1] Raku's constructs for parallelism, concurrency, and asynchrony follow the structured programming paradigm. See Parallelism, Concurrency, and Asynchrony in Raku for Jonathan Worthington's video presentation of this overall approach. Structured constructs like react can cleanly observe, contain, and manage events that occur anywhere within their execution scope, including errors such as error exceptions, even if they happen on other threads.
You seem to be fine now but when I first saw this I made this https://github.com/jonathanstowe/Cro-MQTT which turns the MQTT client into a first class Cro service.
I haven't released it yet but it may be instructive.
So Rx is single-threaded by default. In the case of the Sample operator it's not. In my ASPNetCore application, I want to be able to have Subscribe run on the main thread (single thread). I tried using ObserveOn passing in SynchronizationContext.Current, but it's null in ASPNetCore.
A possible solution will be to push all items into BlockingCollection then read from it, but that kinda adds another layer of complexity.
Console.WriteLine ($"Main Thread: {Thread.CurrentThread.ManagedThreadId}");
var source = Observable
.Interval (TimeSpan.FromSeconds (1))
.Sample (TimeSpan.FromSeconds (2));
source
.Subscribe (
data => {
Console.WriteLine ($"{Thread.CurrentThread.ManagedThreadId}"); // different thread
// Here each onNext is invoked asynchronously
// But I have a shared resource that I would like to invoke synchronously.
}
);
Any recommendations will be greatly appreciated :).
If you want to schedule it on the main thread, you should specify a scheduler for your operators.
var source = Observable
.Interval(TimeSpan.FromSeconds(1))
.Sample(TimeSpan.FromSeconds(2), Scheduler.CurrentThread);
Please note that this is blocking (since it's doing work on the main thread) - which is similar to your enumerable sample.
Also see this answer by #Enigmativity.
I am very new to NServiceBus, and in one of our project, we want to accomplish following -
Whenever table data is modified in Sql server, construct a message and insert in sql server broker queue
Read the broker queue message using NServiceBus
Publish the message again as another event so that other subscribers
can handle it.
Now it is point 2, that I do not have much clue, how to get it done.
I have referred the following posts, after which I was able to enter the message in broker queue, but unable to integrate with NServiceBus in our project, as the NServiceBus libraries are of older version and also many methods used are deprecated. So using them with current versions is getting very troublesome, or if I was doing it in improper way.
http://www.nullreference.se/2010/12/06/using-nservicebus-and-servicebroker-net-part-2
https://github.com/jdaigle/servicebroker.net
Any help on the correct way of doing this would be invaluable.
Thanks.
I'm using the current version of nServiceBus (5), VS2013 and SQL Server 2008. I created a Database Change Listener using this tutorial, which uses SQL Server object broker and SQLDependency to monitor the changes to a specific table. (NB This may be deprecated in later versions of SQL Server).
SQL Dependency allows you to use a broad selection of all the basic SQL functionality, although there are some restrictions that you need to be aware of. I modified the code from the tutorial slightly to provide better error information:
void NotifyOnChange(object sender, SqlNotificationEventArgs e)
{
// Check for any errors
if (#"Subscribe|Unknown".Contains(e.Type.ToString())) { throw _DisplayErrorDetails(e); }
var dependency = sender as SqlDependency;
if (dependency != null) dependency.OnChange -= NotifyOnChange;
if (OnChange != null) { OnChange(); }
}
private Exception _DisplayErrorDetails(SqlNotificationEventArgs e)
{
var message = "useful error info";
var messageInner = string.Format("Type:{0}, Source:{1}, Info:{2}", e.Type.ToString(), e.Source.ToString(), e.Info.ToString());
if (#"Subscribe".Contains(e.Type.ToString()) && #"Invalid".Contains(e.Info.ToString()))
messageInner += "\r\n\nThe subscriber says that the statement is invalid - check your SQL statement conforms to specified requirements (http://stackoverflow.com/questions/7588572/what-are-the-limitations-of-sqldependency/7588660#7588660).\n\n";
return new Exception(messageMain, new Exception(messageInner));
}
I also created a project with a "database first" Entity Framework data model to allow me do something with the changed data.
[The relevant part of] My nServiceBus project comprises two "Run as Host" endpoints, one of which publishes event messages. The second endpoint handles the messages. The publisher has been setup to IWantToRunAtStartup, which instantiates the DBListener and passes it the SQL statement I want to run as my change monitor. The onChange() function is passed an anonymous function to read the changed data and publish a message:
using statements
namespace Sample4.TestItemRequest
{
public partial class MyExampleSender : IWantToRunWhenBusStartsAndStops
{
private string NOTIFY_SQL = #"SELECT [id] FROM [dbo].[Test] WITH(NOLOCK) WHERE ISNULL([Status], 'N') = 'N'";
public void Start() { _StartListening(); }
public void Stop() { throw new NotImplementedException(); }
private void _StartListening()
{
var db = new Models.TestEntities();
// Instantiate a new DBListener with the specified connection string
var changeListener = new DatabaseChangeListener(ConfigurationManager.ConnectionStrings["TestConnection"].ConnectionString);
// Assign the code within the braces to the DBListener's onChange event
changeListener.OnChange += () =>
{
/* START OF EVENT HANDLING CODE */
//This uses LINQ against the EF data model to get the changed records
IEnumerable<Models.TestItems> _NewTestItems = DataAccessLibrary.GetInitialDataSet(db);
while (_NewTestItems.Count() > 0)
{
foreach (var qq in _NewTestItems)
{
// Do some processing, if required
var newTestItem = new NewTestStarted() { ... set properties from qq object ... };
Bus.Publish(newTestItem);
}
// Because there might be a number of new rows added, I grab them in small batches until finished.
// Probably better to use RX to do this, but this will do for proof of concept
_NewTestItems = DataAccessLibrary.GetNextDataChunk(db);
}
changeListener.Start(string.Format(NOTIFY_SQL));
/* END OF EVENT HANDLING CODE */
};
// Now everything has been set up.... start it running.
changeListener.Start(string.Format(NOTIFY_SQL));
}
}
}
Important The OnChange event firing causes the listener to stop monitoring. It basically is a single event notifier. After you have handled the event, the last thing to do is restart the DBListener. (You can see this in the line preceding the END OF EVENT HANDLING comment).
You need to add a reference to System.Data and possibly System.Data.DataSetExtensions.
The project at the moment is still proof of concept, so I'm well aware that the above can be somewhat improved. Also bear in mind I had to strip out company specific code, so there may be bugs. Treat it as a template, rather than a working example.
I also don't know if this is the right place to put the code - that's partly why I'm on StackOverflow today; to look for better examples of ServiceBus host code. Whatever the failings of my code, the solution works pretty effectively - so far - and meets your goals, too.
Don't worry too much about the ServiceBroker side of things. Once you have set it up, per the tutorial, SQLDependency takes care of the details for you.
The ServiceBroker Transport is very old and not supported anymore, as far as I can remember.
A possible solution would be to "monitor" the interesting tables from the endpoint code using something like a SqlDependency (http://msdn.microsoft.com/en-us/library/62xk7953(v=vs.110).aspx) and then push messages into the relevant queues.
.m
What is a good case/example for using the ScheduledDisposable in Reactive Rx
I like the using the CompositeDisposable and SerialDisposable, but would you need the ScheduledDisposable.
The logic of using the Rx disposables is that code that performs some sort of set up operation can return an IDisposable that anonymously contains the code that will do the associated clean up at a later stage. If this pattern is used consistently then you can compose together many disposables to perform a single clean up operation without any specific knowledge of what is being cleaned up.
The problem is that if that clean up code needs to run on a certain thread then you need some way for Dispose called on one thread to be marshalled to required thread - and that's where ScheduledDisposable comes in.
The primary example is the SubscribeOn extension method which uses ScheduledDisposable to ensure that the "unsubscribe" (i.e. the Dispose) is run on the same IScheduler that the Subscribe was run on.
This is important for the FromEventPattern extension method, for example, that attaches to and detaches from event handlers which must happen on the UI thread.
Here's an example of where you might use ScheduledDisposable directly:
var frm = new SomeForm();
frm.Text = "Operation Started.";
var sd = new ScheduledDisposable(
new ControlScheduler(frm),
Disposable.Create(() =>
frm.Text = "Operation Completed."));
Scheduler.ThreadPool.Schedule(() =>
{
// Long-running task
Thread.Sleep(2000);
sd.Dispose();
});
A little contrived, but it should show a reasonable example of how you'd use ScheduledDisposable.