Call async await method in sync calling method

Question

This is only the idea on what im doing in a window service. I get the idea from this video to do it in parallel processing.

I have two different method and a model class.

Model Class code:

public class Email(){
    public string Recipient { get; set; }
    public string Message { get; set; }
}

Methods is something like this:

public void LoadData(){
    while(Main.IsProcessRunning){
        // 1. Get All Emails
        var emails = new dummyRepositories().GetAllEmails(); //This will return List<Emails>.
        // 2. Send it
        // After sending assume that the data will move to other table so it will not be query again for the next loop.
        SendDataParallel(emails);//this will function async? even though the calling method is sync.

        // This will continue here or wait until it already send?
        // If it will continue here even though it will not send already
        // So there's a chance to get the email again for the next loop and send it again?
    }
}

//This will send email at parallel
public async void SendDataParallel(IList<Email> emails){
    var allTasks = emails.Select(SendDataAsync);
    await TaskEx.WhenAll(allTasks);
}

//Assume this code will send email asynchronously. (this will not send email, for sample only)
public async void SendDataAsync(Email email){
    using (var client = new HttpClient())
    {
        client.PostAsync(email);
    }
}

I only want to get all queued emails then send it in parallel then wait until it already send. I'm avoiding using foreach on every email that I get.

What is the question or problem?

Sriram Sakthivel
– Sriram Sakthivel

2015-08-17 09:20:51 +00:00
Commented Aug 17, 2015 at 9:20 — Sriram Sakthivel
– Sriram Sakthivel, Commented Aug 17, 2015 at 9:20
@SriramSakthivel already edited.,.

jmvtrinidad
– jmvtrinidad

2015-08-17 09:33:09 +00:00
Commented Aug 17, 2015 at 9:33 — jmvtrinidad
– jmvtrinidad, Commented Aug 17, 2015 at 9:33
@janmvtrinidad There is still no question here.

Ant P
– Ant P

2015-08-17 09:35:28 +00:00
Commented Aug 17, 2015 at 9:35 — Ant P
– Ant P, Commented Aug 17, 2015 at 9:35
@AntP i put question as a comment in code.,.

jmvtrinidad
– jmvtrinidad

2015-08-17 09:41:12 +00:00
Commented Aug 17, 2015 at 9:41 — jmvtrinidad
– jmvtrinidad, Commented Aug 17, 2015 at 9:41

Yuval Itzchakov · Accepted Answer · 2015-08-18 07:25:46Z

1

Lets start at the bottom:

You dispose your client before you actually finish receiving the HttpResponseMessage asynchronously. You'll need to make your method async Task and await inside:

public async Task SendDataAsync(Email email)
{
    using (var client = new HttpClient())
    {
        var response = await client.PostAsync(email);
    }
}

Currently, your SendDataParallel doesn't compile. Again, it needs to return a Task:

public Task SendEmailsAsync(IList<Email> emails)
{
    var emailTasks = emails.Select(SendDataAsync);
    return Task.WhenAll(allTasks);
}

At the top, you'll need to await on SendEmailsAsync:

public async Task LoadDataAsync()
{
    while (Main.IsProcessRunning)
    {
        var emails = new dummyRepositories().GetAllEmails(); 
        await SendEmailsAsync(emails);
    }
}

Edit:

If you're running this inside a windows service, you can offload it to Task.Run and use the async keyword:

var controller = new Controller();
_processThread = Task.Run(async () => await controller.LoadDataAsync());

edited Aug 18, 2015 at 7:25

answered Aug 17, 2015 at 9:52

Yuval Itzchakov

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6 Comments

jmvtrinidad Over a year ago

It's okay to add static type for LoadDataAsync.,?

Yuval Itzchakov Over a year ago

You want the method to be static?

jmvtrinidad Over a year ago

I will be using LoadData to call as a background service in windows service.,.

Yuval Itzchakov Over a year ago

@janmvtrinidad Ok, but what does that have to do with a static method?

jmvtrinidad Over a year ago

I will create a Thread like this one _processThread = new Thread(Controllers.LoadData) { IsBackground = true };, it needs to be a static to place LoadData as parameters for Thread.

|

Community · Accepted Answer · 2017-05-23 12:06:12Z

1

Doesn't your compiler highlight your code with errors?

If you mark your method as async while it doesn't return any value, you should set your return type as Task, not void:

public async Task SendDataParallel(IList<Email> emails){
    var allTasks = emails.Select(SendDataAsync);
    await Task.WhenAll(allTasks);
}

Your second method also shoud return a Task, otherwise what you want to (a)wait in the first method?

public async Task SendDataAsync(Email email){
    using (var client = new HttpClient())
    {
        return client.PostAsync(email);
    }
}

Now you can Select all your SendDataAsync tasks in SendDataParallel and .Wait() it's task in LoadData in synchronious mode:

public void LoadData(){
    while(Main.IsProcessRunning){
        var emails = new dummyRepositories().GetAllEmails(); //This will return List<Emails>.
        SendDataParallel(emails).Wait();
    }
}

More information you can find reading answers in other SO questions and docs on MSDN:

And as you used LINQ's Select() which is based on foreach cycle next article also could be useful: Nested task inside loop

edited May 23, 2017 at 12:06

CommunityBot

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answered Aug 17, 2015 at 9:42

Nozim Turakulov

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1 Comment

jmvtrinidad Over a year ago

I will use an wait() on my LoadData().., I think it will have an error on SendDataAsync, there is no await keyword on return.., Anyway thanks for your solution.,.

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