using Polly.Utilities; using System; using System.Threading; using System.Threading.Tasks; namespace Polly.Fallback { public class AsyncFallbackPolicy : AsyncPolicy, IFallbackPolicy, IsPolicy { private Func<Exception, Context, Task> _onFallbackAsync; private Func<Exception, Context, CancellationToken, Task> _fallbackAction; internal AsyncFallbackPolicy(PolicyBuilder policyBuilder, Func<Exception, Context, Task> onFallbackAsync, Func<Exception, Context, CancellationToken, Task> fallbackAction) : base(policyBuilder) { if (onFallbackAsync == null) throw new ArgumentNullException("onFallbackAsync"); _onFallbackAsync = onFallbackAsync; if (fallbackAction == null) throw new ArgumentNullException("fallbackAction"); _fallbackAction = fallbackAction; } protected override Task ImplementationAsync(Func<Context, CancellationToken, Task> action, Context context, CancellationToken cancellationToken, bool continueOnCapturedContext) { return AsyncFallbackEngine.ImplementationAsync(async delegate(Context ctx, CancellationToken ct) { await action(ctx, ct).ConfigureAwait(continueOnCapturedContext); return EmptyStruct.Instance; }, context, cancellationToken, base.ExceptionPredicates, ResultPredicates<EmptyStruct>.None, (DelegateResult<EmptyStruct> outcome, Context ctx) => _onFallbackAsync(outcome.Exception, ctx), async delegate(DelegateResult<EmptyStruct> outcome, Context ctx, CancellationToken ct) { await _fallbackAction(outcome.Exception, ctx, ct).ConfigureAwait(continueOnCapturedContext); return EmptyStruct.Instance; }, continueOnCapturedContext); } protected override Task<TResult> ImplementationAsync<TResult>(Func<Context, CancellationToken, Task<TResult>> action, Context context, CancellationToken cancellationToken, bool continueOnCapturedContext) { throw new InvalidOperationException("You have executed the generic .Execute<TResult> method on a non-generic FallbackPolicy. A non-generic FallbackPolicy only defines a fallback action which returns void; it can never return a substitute TResult value. To use FallbackPolicy to provide fallback TResult values you must define a generic fallback policy FallbackPolicy<TResult>. For example, define the policy as Policy<TResult>.Handle<Whatever>.Fallback<TResult>(/* some TResult value or Func<..., TResult> */);"); } } }