standards-c-sharp

Avoid race conditions with proper synchronization

Be careful to avoid race conditions when state is mutated from multiple threads. Since you cannot await from inside a lock statement, either use a thread safe datatype, or synchronize access manually with a SemaphoreSlim.

Don’t

int value;

Task<int> GetNextValueAsync(int current) { ... }

async Task UpdateValueAsync()
{
    // likely to corrupt if accessed by multiple threads
    value = await GetNextValueAsync(value);
}

Do

var mutex = new SemaphoreSlim(1); // max number of concurrent threads

int value;

Task<int> GetNextValueAsync(int current) { ... }

async Task UpdateValueAsync()
{
    await mutex.WaitAsync();
    try
    {
        value = await GetNextValueAsync(value);
    }
    finally
    {
        mutex.Release();
    }
}

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