When i am set stop point at line with XREAD programm doing nothing. Maybe i need to configure this XREAD command?
public async void ListenTask()
{
var readTask = Task.Run(async () =>
{
while (!Token.IsCancellationRequested)
{
var result = db.StreamRead(streamName, "$", 1);
if (result.Any())
{
var dict = ParseResult(result.Last());
var sb = new StringBuilder();
foreach (var key in dict.Keys)
{
sb.Append(dict[key]);
}
Console.WriteLine(sb.ToString());
}
await Task.Delay(1000);
}
});
}
It's an illegal operation on StackExchange.Redis
Because of its unique multiplexed architecture, StackExchange.Redis (the library you appear to be using) does not support blocking XREAD operations. This is because all the commands going over the interactive interface (basically everything non-pub/sub) uses the same connection. If you block one of those connections, everything else in your app dependent on the multiplexer will be backed up awaiting the block to complete. The StackExchange.Redis library actually goes so far as to consider the $ id an illegal id, it's only purpose after all is to block. What's most likely happening (you don't see it happen because it's being swallowed up by the synchronization context) is that var result = db.StreamRead(streamName, "$", 1); is throwing an InvalidOperationException: System.InvalidOperationException: StreamPosition.NewMessages cannot be used with StreamRead.
Work Arounds
There are 2 potential workarounds in this case, first, you can use poll with XRANGE command rather than using blocking reads.
var readTask = Task.Run(async () =>
{
var lastId = "-";
while (!token.IsCancellationRequested)
{
var result = await db.StreamRangeAsync("a-stream", lastId, "+");
if(result.Any()
{
lastId = result.Last().Id;
}
await Task.Delay(1000);
}
});
You're already effectively doing a thread sleep so this polling operation is probably good enough for what you're looking for.
If you really need to do blocking operations, you'll have to use a different library, if you try to use StackExchange.Redis (you can possibly force the issue with the Execute/ExecuteAsync commands) you can seriously negatively degrade its performance.
Articles on doing so with ServiceStack.Redis and CsRedis are available on the redis developer site (I'm the author of them)
One final thing
Probably want to make sure that when you are issuing these commands that you are being as async as possible, you're using the sync XREAD command in an Async context (mostly every command in StackExchange.Redis has a sync/async version you can use - use the async when possible).
Related
I have an action method which needs to complete 15~52 long running SQL queries (all of them are similar, each takes more than 5 seconds to complete) according to user-selected dates.
After doing a lot of research, it seems the best way to do this without blocking the ASP.Net thread is to use async/await task methods With SQL Queries:
[HttpPost]
public async Task<JsonResult> Action() {
// initialization stuff
// create tasks to run async SQL queries
ConcurrentBag<Tuple<DateTime, List<long>>> weeklyObsIdBag =
new ConcurrentBag<Tuple<DateTime, List<long>>>();
Task[] taskList = new Task[reportDates.Count()];
int idx = 0;
foreach (var reportDate in reportDates) { //15 <= reportDates.Count() <= 52
var task = Task.Run(async () => {
using (var sioDbContext = new SioDbContext()) {
var historyEntryQueryable = sioDbContext.HistoryEntries
.AsNoTracking()
.AsQueryable<HistoryEntry>();
var obsIdList = await getObsIdListAsync(
historyEntryQueryable,
reportDate
);
weeklyObsIdBag.Add(new Tuple<DateTime,List<long>>(reportDate, obsIdList));
}
});
taskList[idx++] = task;
}
//await for all the tasks to complete
await Task.WhenAll(taskList);
// consume the results from long running SQL queries,
// which is stored in weeklyObsIdBag
}
private async Task<List<long>> getObsIdListAsync(
IQueryable<HistoryEntry> historyEntryQueryable,
DateTime reportDate
) {
//apply reportDate condition to historyEntryQueryable
//run async query
List<long> obsIdList = await historyEntryQueryable.Select(he => he.ObjectId)
.Distinct()
.ToListAsync()
.ConfigureAwait(false);
return obsIdList;
}
After making this change, the time taken to complete this action is greatly reduced since now I am able to execute multiple (15~52) async SQL queries simultaneously and await for them to complete rather than running them sequentially. However, users start to experience lots of time out issues, such as :
(from Elmah error log)
"Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool.
This may have occurred because all pooled connections were in use and max pool size was
reached."
"The wait operation timed out"
Is it caused by thread starvation? I got a feeling that I might be using too many threads from thread pool to achieve what I want, but I thought it shouldn't be a problem because I used async/await to prevent all the threads from being blocked.
If things won't work this way, then what's the best practice to execute multiple long running SQL queries?
Consider limiting the number of concurrent tasks being executed, for example:
int concurrentTasksLimit = 5;
List<Task> taskList = new List<Task>();
foreach (var reportDate in reportDates) { //15 <= reportDates.Count() <= 52
var task = Task.Run(async () => {
using (var sioDbContext = new SioDbContext()) {
var historyEntryQueryable = sioDbContext.HistoryEntries
.AsNoTracking()
.AsQueryable<HistoryEntry>();
var obsIdList = await getObsIdListAsync(
historyEntryQueryable,
reportDate
);
weeklyObsIdBag.Add(new Tuple<DateTime,List<long>>(reportDate, obsIdList));
}
});
taskList.Add(task);
if (concurrentTasksLimit == taskList.Count)
{
await Task.WhenAll(taskList);
// before clearing the list, you should get the results and store in memory (e.g another list) for later usage...
taskList.Clear();
}
}
//await for all the remaining tasks to complete
if (taskList.Any())
await Task.WhenAll(taskList);
Take note I changed your taskList to an actual List<Task>, it just seems easier to use it, since we need to add/remove tasks from the list.
Also, you should get the results before clearing the taskList, since you are going to use them later.
I'm creating an app that requires todo parallel http request, I'm using HttpClient for this.
I'm looping over the urls and foreach URl I start a new Task todo the request.
after the loop I wait untill every task finishes.
However when I check the calls being made with fiddler I see that the request are being called synchronously. It's not like a bunch of request are being made, but one by one.
I've searched for a solution and found that other people have experienced this too, but not with UWP. The solution was to increase the DefaultConnectionLimit on the ServicePointManager.
The problem is that ServicePointManager does not exist for UWP. I've looked in the API's and I thought I could set the DefaultConnectionLimit on HttpClientHandler, but no.
So I have a few Questions.
Is DefaultConnectionLimit still a property that could be set somewhere?
if so, where do i set it?
if not, how do I increase the connnectionlimit?
Is there still a connectionlimit in UWP?
this is my code:
var requests = new List<Task>();
var client = GetHttpClient();
foreach (var show in shows)
{
requests.Add(Task.Factory.StartNew((x) =>
{
((Show)x).NextEpisode = GetEpisodeAsync(((Show)x).NextEpisodeUri, client).Result;}, show));
}
}
await Task.WhenAll(requests.ToArray());
and this is the request:
public async Task<Episode> GetEpisodeAsync(string nextEpisodeUri, HttpClient client)
{
try
{
if (String.IsNullOrWhiteSpace(nextEpisodeUri)) return null;
HttpResponseMessage content; = await client.GetAsync(nextEpisodeUri);
if (content.IsSuccessStatusCode)
{
return JsonConvert.DeserializeObject<EpisodeWrapper>(await content.Content.ReadAsStringAsync()).Episode;
}
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
return null;
}
Oke. I have the solution. I do need to use async/await inside the task. The problem was the fact I was using StartNew instead of Run. but I have to use StartNew because i'm passing along a state.
With the StartNew. The task inside the task is not awaited for unless you call Unwrap. So Task.StartNew(.....).Unwrap(). This way the Task.WhenAll() will wait untill the inner task is complete.
When u are using Task.Run() you don't have to do this.
Task.Run vs Task.StartNew
The stackoverflow answer
var requests = new List<Task>();
var client = GetHttpClient();
foreach (var show in shows)
{
requests.Add(Task.Factory.StartNew(async (x) =>
{
((Show)x).NextEpisode = await GetEpisodeAsync(((Show)x).NextEpisodeUri, client);
}, show)
.Unwrap());
}
Task.WaitAll(requests.ToArray());
I think an easier way to solve this is not "manually" starting requests but instead using linq with an async delegate to query the episodes and then set them afterwards.
You basically make it a two step process:
Get all next episodes
Set them in the for each
This also has the benefit of decoupling your querying code with the sideeffect of setting the show.
var shows = Enumerable.Range(0, 10).Select(x => new Show());
var client = new HttpClient();
(Show, Episode)[] nextEpisodes = await Task.WhenAll(shows
.Select(async show =>
(show, await GetEpisodeAsync(show.NextEpisodeUri, client))));
foreach ((Show Show, Episode Episode) tuple in nextEpisodes)
{
tuple.Show.NextEpisode = tuple.Episode;
}
Note that i am using the new Tuple syntax of C#7. Change to the old tuple syntax accordingly if it is not available.
I have a requirement to a batch a number of web service calls on the receipt of a single message appearing in a (MSMQ) queue.
Is "sagas" the way to go?
The interaction with the 3rd party web service is further complicated because I need to call it once, then poll subsequently for an acknowledgement with a correlation id, returned in the reply to the initial call to the web service.
Yes, sagas could be the way to coordinate the process of initiating the call, polling until the operation has ended, and then doing something else when all the work is done.
If you don't care too much about accidentally making the web service call more than once, you can easily use Rebus' async capabilities to implement the polling - I am currently in the process of building something that basically does this:
public async Task Handle(SomeMessage message)
{
var response = await _client.Get<SomeResponse>("https://someurl") ;
var pollUrl = response.PollUrl;
var resultUrl = response.ResultUrl;
while(true)
{
var result = await _client.Get<PollResult>(pollUrl);
if (result.Status == PollStatus.Processing)
{
await Task.Delay(TimeSpan.FromSeconds(2));
continue;
}
if (result.Status == PollStatus.Done)
{
var finalResult = await _client.Get<FinalResult>(resultUrl);
return new SomeReply(finalResult);;
}
throw new Exception($"Unexpected status while polling {pollUrl}: {result.Status}")
}
}
thus taking advantage of async/await to poll the external webservice while it is processing, while consuming minimal resources in our end.
I found an interesting differences between .NET Framework's HttpClient class/objects and the VS-2013 Project PhotoServer (DLL) class/objects. It made me wonder if there's a bug with the script.
I'm using .NET Framework v4.5.1.
I'm using the HttpClient script in the sychronous Web Generic Handler. Noticed that I'm using the ".Result" for the asynchronous POST to wait for response. So, looking at HttpClient which works is
using (var httpClient = new HttpClient())
{
var response = httpClient.PostAsync(
_baseUrl,
new FormUrlEncodedContent
(
new List<KeyValuePair<string, string>>
{
new KeyValuePair<string, string>("Vin", parmVin),
new KeyValuePair<string, string>("ImageSize", parmImageSize)
}.ToArray()
)
).Result;
//returned string[] datatype...
var photoUrls = response.Content.ReadAsStringAsync().Result;
}
I'm using the "GetPhotoUrlsAsync" script in the sychronous Web Generic Handler. This "GetPhotoUrlsAsync" object comes from the Project class (DLL). Again, I'm using the ".Result" and it doesn't work, it just deadlocked and hung. What I wanna know is why is that and was there a bug with the script?
//[Scripts in Web Generic Handlers]...
var managerVehiclePhoto = new ManagerVehiclePhoto();
var photoUrls = managerVehiclePhoto.GetPhotoUrlsAsync("12345678901234567").Result;
//[Project Class]...
namespace BIO.Dealer.Integration.PhotoServer
{
public seal class VehiclePhotoManager
{
public async Task<string[]> GetPhotoUrlsAsync(string vin)
{
var listResponse = await _client.ListAsync(vin);
return listResponse.ToArray();
}
}
}
Thanks...
Edit #1
//Synchronous API Call...
public string[] GetPhotoUrls(string vin)
{
return GetPhotoUrlsAsync(vin).Result;
}
Using .Result like this is actually a bug in both cases; it just happens not to deadlock in the HttpClient case. Note that the same HttpClient library on other platforms (notably Windows Phone, IIRC) will deadlock if used like this.
I describe the deadlock in detail on my blog, but the gist of it is this:
There's an ASP.NET "request context" that is captured by default every time you use await. When the async method resumes, it will resume within that context. However, types such as HttpContext are not multithread-safe, so ASP.NET restricts that context to one thread at a time. So if you block a thread by calling .Result, it's blocking a thread inside that context.
The reason GetPhotoUrlsAsync deadlocks is because it's an async method that is attempting to resume inside that context, but there is already a thread blocked in that context. The reason HttpClient happens to work is because GetAsync etc. are not actually async methods (note that this is an implementation detail and you should not depend on this behavior).
The best way to fix this is to replace .Result with await:
var managerVehiclePhoto = new ManagerVehiclePhoto();
var photoUrls = await managerVehiclePhoto.GetPhotoUrlsAsync("12345678901234567");
Me again (re: same quest WebPages async) :) That said, I'm one of those that Stephen Cleary identifies as "trying to migrate into async", so all this is (still) a learning moment.
The issue is SynchronizationContext in GUI/ASP.Net. I won't mangle Stephen's explanation so the link is your best bet to grok.
Given the best practices in that article, here's my way (consequently what I use in WebPages for the "top level call") to "mock" awaiting a PostAsync call like what you're doing. In this case I'm using ConfigureAwait (call is from WebPages, not MVC):
public static async Task<string> PostToRequestBin()
{
var _strContent = new FormUrlEncodedContent(new[] {new KeyValuePair<string,string>("fizz","buzz")});
using (var client = new HttpClient())
{
/*
* See http://requestb.in/ for usage
*/
var result = await client.PostAsync("http://requestb.in/xyzblah", _strContent).ConfigureAwait(false);
return await result.Content.ReadAsStringAsync();
}
}
In my WebPages page:
#{
//Class2 is a mock "library" in App_Code where the above async code lives
var postcatcher = Class2.PostToRequestBin();
}
And to make use of it somewhere in the page (where I make use of Task<string>.Result:
<p>#postcatcher.Result</p>
Again, this is a learning moment and I hope it helps/guides you. I fully expect the SO community to comment and or correct/improve on this like:
"Why don't I have to ConfigureAwait on ReadAsStringAsync" (it works either way)?
because at this point, it's "async all the way". I could have awaited some other async method...
...so the learning moments continue :)
I have been experimenting with a lightweight solution for handling my business logic. It consists of a vanilla ADO.NET connection that is extended with Dapper, and monitored by Glimpse.ADO. The use case for this setup will be a web application that has to process a handful of queries asynchronously per request. Below a simple implementation of my setup in an MVC controller.
public class CatsAndDogsController : Controller
{
public async Task<ActionResult> Index()
{
var fetchCatsTask = FetchCats(42);
var fetchDogsTask = FetchDogs(true);
await Task.WhenAll(fetchCatsTask, fetchDogsTask);
ViewBag.Cats = fetchCatsTask.Result;
ViewBag.Dogs = fetchDogsTask.Result;
return View();
}
public async Task<IEnumerable<Cat>> FetchCats(int breedId)
{
IEnumerable<Cat> result = null;
using (var connection = CreateAdoConnection())
{
await connection.OpenAsync();
result = await connection.QueryAsync<Cat>("SELECT * FROM Cat WHERE BreedId = #bid;", new { bid = breedId });
connection.Close();
}
return result;
}
public async Task<IEnumerable<Dog>> FetchDogs(bool isMale)
{
IEnumerable<Dog> result = null;
using (var connection = CreateAdoConnection())
{
await connection.OpenAsync();
result = await connection.QueryAsync<Dog>("SELECT * FROM Dog WHERE IsMale = #im;", new { im = isMale });
connection.Close();
}
return result;
}
public System.Data.Common.DbConnection CreateAdoConnection()
{
var sqlClientProviderFactory = System.Data.Common.DbProviderFactories.GetFactory("System.Data.SqlClient");
var dbConnection = sqlClientProviderFactory.CreateConnection();
dbConnection.ConnectionString = "SomeConnectionStringToAwesomeData";
return dbConnection;
}
}
I have some questions concerning the creation of the connection in the CreateAdoConnection() method. I assume the following is happening behind the scenes.
The call to sqlClientProviderFactory.CreateConnection() returns an instance of System.Data.SqlClient.SqlConnection passed as a System.Data.Common.DbConnection. At this point Glimpse.ADO.AlternateType.GlimpseDbProviderFactory kicks in and wraps this connection in an instance of Glimpse.Ado.AlternateType.GlimpseDbConnection, which is also passed as a System.Data.Common.DbConnection. Finally, this connection is indirectly extended by the Dapper library with its query methods, among them the QueryAsync<>() method used to fetch the cats and dogs.
The questions:
Is the above assumption correct?
If I use Dapper's async methods with this connection - or create a System.Data.Common.DbCommand with this connection's CreateCommand() method, and use it's async methods - will those calls internally always end up using the vanilla async implementations of these methods as Microsoft has written them for System.Data.SqlClient.SqlConnection and System.Data.SqlClient.SqlCommand? And not some other implementations of these methods that are actually blocking?
How much perf do I lose with this setup compared to just returning a new System.Data.SqlClient.SqlConnection directly? (So, without the Glimpse.ADO wrapper)
Any suggestions on improving this setup?
Yes pretty much. GlimpseDbProviderFactory wraps/decorates/proxies all the registered factories. We then pass any calls we get through to the factory we wrap (in this case SQL Server). In the case of CreateConnection() we ask the inner factory we have, to create a connection, when we get that connection, we wrap it and then return it to the originating caller
Yes. Glimpse doesn't turn what was an async request into a blocking request. We persevere the async chain all the way though. If you are interested, the code in question is here.
Very little. In essence, using a decorator pattern like this adds only one or two frames to the call stack. Compared to most operations performed during the request lifecycle, the time to observe whats happening here is extremely minimal.
What you have looks great. Only suggestion is to maybe us this code to build the factory. This code means that you can shift your connection string, etc to the web.config.