250116 ‐ more on async - cywongg/2025 GitHub Wiki

Ah, I see! If restrikingValidationService.Init(myInstruments.Values) is not asynchronous, then using Task.Run in this specific case can make sense, but it depends on the nature of the work being done. Let’s clarify and analyze whether Task.Run is appropriate here.

1. For CPU-bound Operations:
   If restrikingValidationService.Init(myInstruments.Values) is a CPU-intensive task (e.g., computationally heavy processing, data transformations, etc.), then wrapping it in Task.Run is appropriate because it offloads the computation to a thread pool thread, ensuring that the UI thread remains free to handle user interactions.

2. For Blocking I/O Operations:
   If restrikingValidationService.Init(myInstruments.Values) involves blocking I/O (e.g., synchronous database queries, API calls, file system operations, etc.), then wrapping it in Task.Run is also acceptable. While it’s better to rewrite such methods to be truly asynchronous (e.g., using async/await or I/O-specific libraries), Task.Run can mitigate the impact of blocking the UI thread.

3. When You Need to Avoid Blocking the UI Thread:
   If Init runs long enough to risk freezing the UI (e.g., taking several seconds), Task.Run is a reasonable workaround to ensure the UI remains responsive.

However, if Init is neither CPU-bound nor blocking I/O, then Task.Run is unnecessary and introduces extra overhead.

Since restrikingValidationService.Init(myInstruments.Values) is not async, using Task.Run is valid if:

1. It performs CPU-bound or blocking I/O operations.
2. You want to run it concurrently with other tasks.

Here’s what happens under the hood with Task.Run:

• Task.Run queues the Init method to run on a thread pool thread.
• The Task returned by Task.Run is awaited, so the UI thread remains free to process other events during execution.
• This allows the Init method to run concurrently with the second task (corporateActionTask).

If you don’t use Task.Run, the synchronous Init method will execute on the UI thread, blocking it until the method completes.

The ideal solution is to refactor restrikingValidationService.Init to be asynchronous if it involves blocking I/O or long-running operations. For example:

• If it performs database calls, use async database libraries (e.g., Entity Framework’s ToListAsync).
• If it makes synchronous API calls, use HttpClient’s SendAsync.
• If it reads files, use FileStream’s async methods.

This would eliminate the need for Task.Run. However, if refactoring is not feasible, Task.Run is a reasonable workaround.

Using Task.Run introduces some overhead:

• It schedules the work on the thread pool, which incurs a small cost.
• If Init is already lightweight, the overhead of switching threads may outweigh the benefits of offloading it.

Ensure proper exception handling and cancellation support. For example, if the Task.Run task fails, you should handle exceptions gracefully. Use try-catch around Task.WhenAll to manage exceptions.

If restrikingValidationService.Init cannot be made asynchronous and you want to keep it responsive, your current approach is fine. Here’s the updated code:

public async Task HandleAsiaSpecificLogicAsync()
{
    // Log the start
    Elastic.AddLog("Start processing Destriking check & CA");

    // Start both tasks concurrently
    Task restrikingCheckTask = Task.Run(() => restrikingValidationService.Init(myInstruments.Values)); // Use Task.Run for the synchronous method
    Task corporateActionTask = CorporateActionInitAsync(); // Async task

    try
    {
        // Await both tasks concurrently
        await Task.WhenAll(restrikingCheckTask, corporateActionTask);
    }
    catch (Exception ex)
    {
        // Handle exceptions from either task
        Elastic.AddLog("Error during Destriking check or Corporate Action processing", ex);
        throw; // Re-throw if necessary
    }

    // Log completion
    Elastic.AddLog("Restriking check & CA processed successfully");
}

private async Task CorporateActionInitAsync()
{
    // Fetch required data
    ICollection<string> prIndexes = GetPrIndexes();
    ICollection<string> prStocks = GetPrStocks();
    DateTime latestNextFixingDate = GetLatestNextFixingDate();

    // Call the async method for corporate action service
    await corporateActionService.Init(prIndexes, prStocks, DateTime.Today, latestNextFixingDate);
}

Here’s how the threads behave in this setup:

1. UI Thread Starts:
   The UI thread calls HandleAsiaSpecificLogicAsync().

2. restrikingCheckTask Runs on a Thread Pool Thread:

   • The Task.Run call queues restrikingValidationService.Init to run on a thread pool thread.
   • The UI thread is immediately released after queuing this task.

3. CorporateActionInitAsync Runs on the UI Thread Until Awaited:

   • The async method begins execution on the UI thread.
   • When it hits the first await (e.g., await corporateActionService.Init), the UI thread is released.

4. Task.WhenAll Waits for Both Tasks:

   • The await Task.WhenAll pauses execution of HandleAsiaSpecificLogicAsync until both tasks complete.
   • The UI thread remains free to process other messages during this time.

5. Tasks Complete:
   Once both restrikingCheckTask and corporateActionTask finish, the method resumes execution on the UI thread.

• Using Task.Run Here Is Fine, given that restrikingValidationService.Init is synchronous and cannot be changed to async. It ensures the UI thread isn’t blocked.
• However, if Init can be made asynchronous, refactor it to avoid Task.Run. This is a cleaner and more efficient solution.

1. Avoid Task.Run Unless Necessary:
   Use it only for CPU-bound or blocking synchronous code that cannot be made asynchronous.

2. Refactor Synchronous Code to Async:
   Whenever possible, update synchronous methods to leverage async APIs for better performance and scalability.

3. Monitor Overhead:
   Be cautious about the overhead of switching threads with Task.Run. For lightweight synchronous methods, it might not be worth it.

4. Handle Exceptions Gracefully:
   Use try-catch blocks with Task.WhenAll to handle exceptions from concurrent tasks.

By following these principles, you ensure that your UI remains responsive while maintaining clean, efficient, and maintainable code.

Yes, the line

issueDateByBasket[instrument.BasketInstrumentID] = instrument.IssueDate;

adds or updates an entry in the issueDateByBasket dictionary. Here's a breakdown of what it does:

1. uniqueBasketInstrumentIds.Add(instrument.BasketInstrumentID):

   • This attempts to add the BasketInstrumentID to the HashSet.
   • If the BasketInstrumentID is already in the HashSet, the Add method returns false, and the body of the if block is skipped.
   • If the BasketInstrumentID is not in the HashSet, the Add method returns true, meaning it's a unique ID, and the code inside the if block is executed.

2. issueDateByBasket[instrument.BasketInstrumentID] = instrument.IssueDate;:

   • If the BasketInstrumentID does not already exist in the issueDateByBasket dictionary, this line adds a new key-value pair to the dictionary where:
     • The key is instrument.BasketInstrumentID.
     • The value is instrument.IssueDate.
   • If the BasketInstrumentID already exists in the issueDateByBasket dictionary (although in this case it won't, because of the HashSet check), this line would update the value associated with the key.

• The HashSet ensures that each BasketInstrumentID is processed only once by filtering out duplicates.
• The dictionary (issueDateByBasket) is populated or updated only for unique BasketInstrumentID values due to the HashSet check.

In this code, the line issueDateByBasket[instrument.BasketInstrumentID] = instrument.IssueDate; adds a new entry to the dictionary for each unique BasketInstrumentID. If the BasketInstrumentID is a duplicate, the dictionary is not modified at all for that particular instrument.

To prevent a number from showing in scientific notation in XAML, you can apply a StringFormat directly in the Binding. This allows you to control how the number is displayed. Here's how you can update your XAML to fix this issue:

<GridViewColumn DisplayMemberBinding="{Binding Path=(77).CurrentA, StringFormat=N}">
    <GridViewColumn.Header>
        <GridViewColumnHeader Content="CurrentA" MinWidth="100" Name="CurrentA" />
    </GridViewColumn.Header>
</GridViewColumn>

1. StringFormat=N:

   • This ensures the number is displayed in a standard numeric format (not in scientific notation).
   • You can also use more specific formats, e.g., "N2" for two decimal places, "F3" for fixed-point with three decimal places, etc.

2. Updated Binding:

   • The StringFormat is applied directly in the Binding, so no changes are needed in your data model or code-behind.

If you want to display the number with two decimal places, you can use:

<GridViewColumn DisplayMemberBinding="{Binding Path=(77).CurrentA, StringFormat=N2}">
    <GridViewColumn.Header>
        <GridViewColumnHeader Content="CurrentA" MinWidth="100" Name="CurrentA" />
    </GridViewColumn.Header>
</GridViewColumn>

This will ensure your number is always displayed in a readable format without scientific notation.