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With threads you could use Semaphore, mutex, ManualResetEvent, etc... to sync a shared data, how do you accomplish the same thing with tasks? Essentially, if I have shared data between different tasks that run on the thread pool with Task.run() or that resume on the thread pool on a random thread after an async event, how would I sync them up if they share data?

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  • Sharing your research helps everyone. Tell us what you've tried and why it didn't meet your needs. This demonstrates that you've taken the time to try to help yourself, it saves us from reiterating obvious answers, and most of all it helps you get a more specific and relevant answer. Also see How to Ask Commented Apr 14, 2021 at 22:54
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    With semaphore specifically, just use waitasync on the semaphoreslim. Commented Apr 14, 2021 at 22:57
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    For Tasks, use WhenAll. Commented Apr 15, 2021 at 4:34
  • @RobertHarvey: The question body mentions shared data between tasks, so I doubt this is as simple as Task.WhenAll. Commented Apr 15, 2021 at 11:09
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    Have you tried the lock-free collections? docs.microsoft.com/en-us/dotnet/standard/collections/… ; otherwise, have you considered designing to not require shared data? Commented Apr 15, 2021 at 16:14

1 Answer 1

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You need a lock that allows you to await it rather than block. This functionality is offered by the SemaphoreSlim class.

SemaphoreSlim _semaphore = new SemaphoreSlim(1);

async Task HandleLockedResource() 
{
    await _semaphore.WaitAsync();

    try
    {
        await DoSomethingWithLockedResource();
    }
    finally
    {
        _semaphore.Release();
    }
}

See also How to combine async with locking and What is the best practice using async in lock

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