Rx.Net memory leak

Question

An interesting memory leak. Does anyone know why?

foreach (int x in Enumerable.Range(0, 1_000_000)
    .Select(async i => i))
{
}

GC.Collect();
Console.WriteLine(GC.GetTotalAllocatedBytes()); // 1036542160

foreach (int x in Enumerable.Range(0, 1_000_000)
    .Select(async i => i))
{
}

GC.Collect();
Console.WriteLine(GC.GetTotalAllocatedBytes()); // 2072860704

foreach (int x in Enumerable.Range(0, 1_000_000)
    .Select(async i => i))
{
}

GC.Collect();
Console.WriteLine(GC.GetTotalAllocatedBytes()); // 3109160008

Where:

static class SelectAsync
{
    public static IEnumerable<TResult> Select<T, TResult>(
        this IEnumerable<T> source, Func<T, Task<TResult>> selector) =>
        source
            .ToObservable()
            .Select(value => Observable.FromAsync(() => selector(value)))
            .Concat()
            .ToEnumerable();        
}

Answer 1

There's actually no memory leak.

GC.GetTotalAllocatedBytes is a count of the bytes allocated over the lifetime of the process. Every time there's a heap allocation, this counter goes up.

What you want to use instead is GC.GetTotalMemory .

If you see the deltas between your test values, you'll see that they're approximately the same.

You'll see some minor variations in your tests related to memory pressure.