Why should you care?

ShopNest inventory outage should not exhaust threads on every product page request.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public sealed class CircuitBreaker
{
    private int _failures;
    private DateTime _openUntil = DateTime.MinValue;
    public async Task<T> ExecuteAsync<T>(Func<Task<T>> action)
    {
        if (DateTime.UtcNow < _openUntil) throw new InvalidOperationException("circuit open");
        try
        {
            var result = await action();
            _failures = 0;
            return result;
        }
        catch
        {
            if (++_failures >= 3) _openUntil = DateTime.UtcNow.AddSeconds(30);
            throw;
        }
    }
}

var cb = new CircuitBreaker();
try { await cb.ExecuteAsync<string>(() => throw new Exception("down")); }
catch { Console.WriteLine("handled"); }

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• After threshold failures the circuit opens and rejects quickly.
• Half-open trials come after cool-down.
• Combine with timeouts and fallbacks.

Practice next

1. Trip the breaker with repeated failures.
2. Observe fast fail while open.
3. Add a fallback “stock unknown”.
4. Reset failures after success.
5. Expose State property Open/Closed.

Remember

Fail fast when sick. Cool-down then trial. Per-dependency breakers.

ShopNest inventory breaker

PDP opens circuit when inventory API dies.

Outcome: Site stays up with degraded stock messaging.