问缓存运行状况检查Net Core

EN

public class HealthCheckCacher : IHealthCheck
{
    private readonly SemaphoreSlim _mutex = new SemaphoreSlim(1);
    private readonly IHealthCheck _healthCheck;
    private readonly TimeSpan _timeToLive;

    private HealthCheckResult _result;
    private DateTime _lastCheck;

    public static readonly TimeSpan DefaultTimeToLive = TimeSpan.FromSeconds(30);

    /// <summary>
    /// Creates a new HealthCheckCacher which will cache the result for the amount of time specified.
    /// </summary>
    /// <param name="healthCheck">The underlying health check to perform.</param>
    /// <param name="timeToLive">The amount of time for which the health check should be cached. Defaults to 30 seconds.</param>
    public HealthCheckCacher(IHealthCheck healthCheck, TimeSpan? timeToLive = null)
    {
        _healthCheck = healthCheck;
        _timeToLive = timeToLive ?? DefaultTimeToLive;
    }

    public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
    {
        // you could improve thread concurrency by separating the read/write logic but this would require additional thread safety checks.
        // will throw OperationCanceledException if the token is canceled while we're waiting.
        await _mutex.WaitAsync(cancellationToken);

        try
        {
            // previous check is cached & not yet expired; just return it
            if (_lastCheck > DateTime.MinValue && DateTime.Now - _lastCheck < _timeToLive)
                return _result;

            // check has not been performed or is expired; run it now & cache the result
            _result = await _healthCheck.CheckHealthAsync(context, cancellationToken);
            _lastCheck = DateTime.Now;

            return _result;
        }
        finally
        {
            _mutex.Release();
        }
    }
}