/// <summary>
/// Builds a <see cref="FallbackPolicy"/> which provides a fallback action if the main execution fails. Executes the main delegate asynchronously, but if this throws a handled exception, first asynchronously calls <paramref name="onFallbackAsync"/> with details of the handled exception and execution context; then asynchronously calls <paramref name="fallbackAction"/>.
/// </summary>
/// <param name="policyBuilder">The policy builder.</param>
/// <param name="fallbackAction">The fallback delegate.</param>
/// <param name="onFallbackAsync">The action to call asynchronously before invoking the fallback delegate.</param>
/// <exception cref="System.ArgumentNullException">fallbackAction</exception>
/// <exception cref="System.ArgumentNullException">onFallbackAsync</exception>
/// <returns>The policy instance.</returns>
public static FallbackPolicy FallbackAsync(this PolicyBuilder policyBuilder, Func <CancellationToken, Task> fallbackAction, Func <Exception, Context, Task> onFallbackAsync)
{
if (fallbackAction == null)
{
throw new ArgumentNullException(nameof(fallbackAction));
}
if (onFallbackAsync == null)
{
throw new ArgumentNullException(nameof(onFallbackAsync));
}
return(new FallbackPolicy(
(action, context, cancellationToken, continueOnCapturedContext) => FallbackEngine.ImplementationAsync(
async(ctx, ct) => { await action(ctx, ct).ConfigureAwait(continueOnCapturedContext); return EmptyStruct.Instance; },
context,
policyBuilder.ExceptionPredicates,
PredicateHelper <EmptyStruct> .EmptyResultPredicates,
(outcome, ctx) => onFallbackAsync(outcome.Exception, ctx),
async ct => { await fallbackAction(ct).ConfigureAwait(continueOnCapturedContext); return EmptyStruct.Instance; },
cancellationToken,
continueOnCapturedContext),
policyBuilder.ExceptionPredicates));
}
/// <summary>
/// Builds a <see cref="FallbackPolicy"/> which provides a fallback value if the main execution fails. Executes the main delegate asynchronously, but if this throws a handled exception or raises a handled result, first asynchronously calls <paramref name="onFallbackAsync"/> with details of the handled exception or result and the execution context; then asynchronously calls <paramref name="fallbackAction"/> and returns its result.
/// </summary>
/// <param name="policyBuilder">The policy builder.</param>
/// <param name="fallbackAction">The fallback delegate.</param>
/// <param name="onFallbackAsync">The action to call asynchronously before invoking the fallback delegate.</param>
/// <exception cref="System.ArgumentNullException">fallbackAction</exception>
/// <exception cref="System.ArgumentNullException">onFallbackAsync</exception>
/// <returns>The policy instance.</returns>
public static FallbackPolicy <TResult> FallbackAsync <TResult>(this PolicyBuilder <TResult> policyBuilder, Func <CancellationToken, Task <TResult> > fallbackAction, Func <DelegateResult <TResult>, Context, Task> onFallbackAsync)
{
if (fallbackAction == null)
{
throw new ArgumentNullException(nameof(fallbackAction));
}
if (onFallbackAsync == null)
{
throw new ArgumentNullException(nameof(onFallbackAsync));
}
return(new FallbackPolicy <TResult>(
(action, context, cancellationToken, continueOnCapturedContext) => FallbackEngine.ImplementationAsync(
action,
context,
policyBuilder.ExceptionPredicates,
policyBuilder.ResultPredicates,
onFallbackAsync,
fallbackAction,
cancellationToken,
continueOnCapturedContext),
policyBuilder.ExceptionPredicates,
policyBuilder.ResultPredicates));
}