如何将两个任务集合链接在一起？

Question

I'm attempting to run a collection of tasks, then once these have finished, run a separate collection of tasks. Essentially, the first collection of tasks are responsible for writing to some database tables, and the final collection of tasks collates the data from these tables into a reporting table.

An example of the code I'm using is below:

var dbWriteTasks = clients.Select(c => DoSomeWorkAsync(c)).ToArray();
var dbCollateTasks = clients.Select(c => DoSomeOtherWorkAsync(c));

Task.Factory.ContinueWhenAll(dbWriteTasks, t => dbCollateTasks.ToArray());

This is running the first set of tasks successfully, but isn't running any of the second set of tasks, so I'm evidently doing something wrong.

I've also tried this to no avail:

var dbWriteTasks = clients.Select(c => DoSomeWorkAsync(c)).ToArray();
var dbCollateTasks = clients.Select(c => DoSomeOtherWorkAsync(c)).ToArray();

Task.Factory.ContinueWhenAll(dbWriteTasks, t => dbCollateTasks);

This runs both sets of tasks, but the second set starts running and processing the data before the first set of tasks has finished inserting it...

I should also mention that I've tried running the two sets of tasks synchronously using Task.WaitAll but this hasn't worked either. I'm trying to do all of this inside an Azure function and Task.WaitAll just causes it to stop.

I'm relatively new to the TPL, so any advice would be greatly appreciated!

Answer 1

Instead of the factory methods use await Task.WhenAll . Using await allows you to seamlessly create continuations that read like synchronous code.

var dbWriteTasks = clients.Select(c => DoSomeWorkAsync(c))
var dbCollateTasks = clients.Select(c => DoSomeOtherWorkAsync(c));

await Task.WhenAll(dbWriteTasks);
await Task.WhenAll(dbCollateTasks);