AwaitMultiple

Await multiple tasks in parallel and get their return values with concise code.

How to use and why

AwaitMultiple can be used like this up to 16 arguments:

var (value1, value2, value3) = await Tasks(task1, task2, task3);

Add:

global using static AwaitMultiple.__Await;

Write

var (books, employees) = await Tasks(
   dbConnection.GetAllAsync<Books>(),
   dbConnection.GetAllAsync<Employees>());

instead of

var books = await dbConnection.GetAllAsync<Book>();
var employees = await dbConnection.GetAllAsync<Employee>();

because the latter code is not executing the employees-related task until the books-related task has finished.

Optional feature

Await tasks with and without return value in a single call:

var (books, employees) = await Tasks(
   dbConnection.GetAllAsync<Books>(),
   dbConnection.GetAllAsync<Employees>(),
   [
      dbConnection.InsertHistoryRecordAsync(),
      // ... any number of tasks...
   ]);

or

var books = await Tasks(
   dbConnection.GetAllAsync<Books>(),
   [
      dbConnection.InsertHistoryRecordAsync(),
      // ... any number of tasks...
   ]);

For code consistency, you can also use:

await Tasks([
   dbConnection.InsertHistoryRecordAsync(),
   // ... any number of tasks...
]);

Exception handling options

By default, only the first occurring exception is thrown (and the others are caught but not re-thrown). This is consistent with Task.WhenAll and more parts of the C# language.

Continue if one task fails

You may want to continue if "getting value b" fails. In that case, you could use the NuGet package TaskExceptionCatcher like this:

var (a, catchResultB, c) = await Tasks(
   StartTaskAAsync(),
   Catcher.Run(() => StartTaskBAsync()),
   StartTaskCAsync());
if (catchResultB.Exception is { } exception)
{
   // no problem!
}
else
{
   var b = catchResultB.Value;
   // use `b`.
}

// use `a` and `c`.

Getting all the exceptions

If you're interested in not only the first, but all the exceptions:

• set the exceptionOption to ExceptionOption.Aggregate
• use Task.Run on all arguments, all tasks.

var (a, b) = await Tasks(
   Task.Run(() => StartTaskAAsync()),
   Task.Run(() => StartTaskBAsync()),
   exceptionOption: ExceptionOption.Aggregate);

Then all errors are returned in a single AggregateException. Its Message property is like:

One or more errors occurred. (First exception message.) (Second exception message.)

Use the property aggregateException.InnerExceptions for more details like StackTraces etc.

Why is Task.Run needed? Because async functions don't return a task until the first await keyword. If an exception occurs before that, then that function throws even before it passes an argument into Tasks.

Configuring awaits

This section is for nerds only. Using ConfigureAwait is NOT necessary.

AwaitMultiple uses .ConfigureAwait(false) internally. Programmers using AwaitMultiple in their own library can use .ConfigureAwait(false):

var (books, employees) = await Tasks(
   dbConnection.GetAllAsync<Books>(),
   dbConnection.GetAllAsync<Employees>())
   .ConfigureAwait(false);

More details:

• The above is slightly better for performance. Normally, after having awaited an async operation, the "context" is set to the same as before the await. That costs time. In most libraries there is no need to capture and return to a specific context, so one might want to set continueOnCapturedContext to false in those libraries.
• Library writers using the above also avoid some deadlock problems for consumers that use their library wrongly.
• In app-level code you will probably not see .ConfigureAwait(false) being used. The performance gain is very small.
• One must not use .ConfigureAwait(false) in a method body that interacts with UI. It is fine to never use it at all.
• Writing await task.ConfigureAwait(true); is functionally identical to await task;, so you never need to use .ConfigureAwait(true).

Conclusion for consumers of this library: You don't need to use ConfigureAwait at all unless you're writing your own library code and want extra performance.

Get it

Available via NuGet.