在 Asp.net Core 中并行运行异步等待任务

Question

List<Employee> employeeList = new List<Employee>();
List<Event> eventList = new List<Event>();

//Wanted to execute each foreach call asynchronously, to improve performance
foreach (var account in accounts)
{
    var context = await GetContext(account); 
    
    //following two await is depends on above result
    var employees = await _employeeService.List(context);
    var events = await _eventService.List(context).ConfigureAwait(false);
    //Question is how to execute above two await calls parallely
    employeeList.AddRange(employees);
    eventList.AddRange(events);
}

我想同时启动两个长期运行的任务（员工和事件）。 那么也许我们可以为上面的每个帐户实现并行执行来解决这个问题？

Answer 1

如果您只希望循环内的每个调用并行 -

List<Employee> employeeList = new List<Employee>();
List<Event> eventList = new List<Event>();
foreach (var account in accounts)
{
    var context = await GetContext(account);
    var employeesTask = _employeeService.List(context);
    var eventsTask = _eventService.List(context);
    await Task.WhenAll(employeesTask , events).ConfigureAwait(false);
    var employees = await employeesTask.ConfigureAwait(false);
    var events= await eventsTask.ConfigureAwait(false);    
    employeeList.AddRange(employees);
    eventList.AddRange(events);
}

Answer 2

您可以将每次迭代的执行安排为TAsk并将其放入数组，然后使用Task.WhenAll ，如下所示：

var tasks = new List<Task>();
//Wanted to execute each foreach call asynchronously, to improve performance
foreach (var account in new int[] { 1 })
{
    tasks.Add(
        Task.Run(async () =>
        {
            var context = await GetContext(account);

            //following two await is depends on above result
            var employees = await _employeeService.List(context);
            var events = await _eventService.List(context).ConfigureAwait(false);
            //Question is how to execute above two await calls parallely
            employeeList.AddRange(employees);
            eventList.AddRange(events);
        }));
}
await Task.WhenAll(tasks);

警告：您必须确保employeeList和eventList是线程安全的。

你甚至可以在一个单独的方法中包装循环迭代（你可以在你的方法中定义它）以使代码更清晰：

await Task.WhenAll(accounts.Select(a => loopIteration(a)));

async Task loopIteration(Account account)
{
    var context = await GetContext(account);

    //following two await is depends on above result
    var employees = await _employeeService.List(context);
    var events = await _eventService.List(context).ConfigureAwait(false);
    //Question is how to execute above two await calls parallely
    employeeList.AddRange(employees);
    eventList.AddRange(events);
}