CallEvent

CallEvent is a readonly struct passed to the Resilience.OnEvent listener. Raising an event is allocation-free, although the Result member boxes value-type results. The Result member is only populated if a listener is attached.

Member	Description
Kind	The type of event that occurred.
PolicyName	The name of the policy (Resilience.Name). This allows a single listener to monitor multiple policies.
AttemptNumber	The 1-based index of the attempt. For Attempt events, it is the attempt that just finished. For Retrying and pre-attempt events, it is the attempt about to run.
Verdict	The classification of the most recent attempt. Defaults to Ok before any attempt has run.
Duration	For Attempt events, this is the duration of that attempt. For all other event kinds, this is the total time the call has been running.
Delay	The duration of the pause about to be served. This is the backoff delay for Retrying events or the rejection pause for Rejected events. This is null for all other event kinds.
Exception	The exception thrown by the most recent attempt, or null if none was thrown.
Result	The value returned by the most recent attempt, as an object. This is null if the attempt threw an exception or returned nothing.
Reason	The StopReason indicating why the call stopped. This is populated only for terminal event kinds.
ToString()	Returns a formatted summary of the event, omitting absent segments.

CallEventKind

The CallEventKind enum defines the types of events emitted during a call.

Kind	Terminal	Delay Populated	Reason Populated
Attempt	No	No	No
Retrying	No	Yes (Backoff)	No
Succeeded	Yes	No	Yes (Succeeded)
NotRetried	Yes	No	Yes (Permanent)
Exhausted	Yes	No	Yes (AttemptsExhausted)
Rejected	Yes	Yes (Rejection pause)	Yes (DependencyUnavailable or BudgetExhausted)
DeadlineExceeded	Yes	No	Yes (DeadlineExceeded)
OrphanedWork	No	No	No
BreakerOpened	No	No	No
BreakerClosed	No	No	No
BreakerHalfOpened	No	No	No
NestedRetry	No	No	No

Event invariants and behavior

• Terminal Events: Every call ends with exactly one terminal event. This invariant ensures that logical operations can be counted reliably.
• Attempt Events: Exactly one Attempt event fires per attempt.
• Retrying Events: Retrying events fire before the backoff delay is served, allowing listeners to report the expected idle time.
• Orphaned Work: OrphanedWork fires when an attempt exceeds its time ceiling by more than one second. This event is raised retrospectively the moment the work finally returns.
• Nested Retries: NestedRetry events are raised exclusively by the HTTP handler.
• Breaker Transitions: Breaker state transitions are raised on the call that triggered the transition, outside of the breaker's internal lock.

Listener contract

The OnEvent listener is executed synchronously on the executor's thread.

• Blocking: If a listener blocks, it blocks the entire call.
• Exceptions: Any exception thrown by a listener is swallowed by the library to prevent telemetry from crashing the application.
• Multiple Listeners: To use multiple listeners, chain them together: OnEvent = first + second.

Log event IDs

The ILogger records a registered policy writes. An event ID is a contract the moment an alert is built on it, so the numbers below are stable and gated by a test. See Logging in DI for how to filter them.

ID	Name	Default	Verbose	Message
1000	AttemptSucceeded	Trace	Information	{Policy} attempt {Attempt} succeeded in {ElapsedMs} ms
1001	AttemptFailed	Debug	Information	{Policy} attempt {Attempt} failed in {ElapsedMs} ms: {Verdict} {ErrorType}
1002	AttemptLimited	Debug	Information	{Policy} attempt {Attempt} was refused by a local limiter before it left the process
1003	Retrying	Debug	Information	{Policy} waiting {DelayMs} ms before attempt {Attempt} after a {Verdict} outcome
1004	CallSucceeded	Trace	Information	{Policy} succeeded in {ElapsedMs} ms
1005	CallSucceededAfterRetries	Debug	Information	{Policy} succeeded on attempt {Attempt} after {ElapsedMs} ms
1006	NotRetried	Debug	Information	{Policy} stopped after attempt {Attempt}: the outcome was classified Permanent
1007	NotRetriedFirstSighting	Warning	Warning	{Policy} did not retry {ErrorType} on attempt {Attempt} because the classifier called it Permanent.
1008	Exhausted	Debug	Information	{Policy} used all {Attempt} attempts in {ElapsedMs} ms and failed with {ErrorType}
1009	DeadlineExceeded	Debug	Information	{Policy} ran out of deadline after {ElapsedMs} ms on attempt {Attempt}
1010	RejectedDependencyUnavailable	Warning	Warning	{Policy} refused a call because its circuit breaker is open. Rejections logged quietly since the previous warning: {Suppressed}.
1011	RejectedBudgetExhausted	Warning	Warning	{Policy} refused a retry because the retry budget is exhausted.
1012	RejectedRepeat	Debug	Information	{Policy} refused a call: {Reason}
1013	BreakerOpened	Warning	Warning	{Policy} opened its circuit breaker on attempt {Attempt}.
1014	BreakerHalfOpened	Information	Information	{Policy} is probing its dependency: the break duration elapsed and this call is the probe
1015	BreakerClosed	Information	Information	{Policy} closed its circuit breaker and is taking traffic again
1016	OrphanedWork	Warning	Warning	{Policy} attempt {Attempt} kept running after its timeout, so that work is still going unobserved.
1017	OrphanedWorkRepeat	Debug	Information	{Policy} attempt {Attempt} kept running after its timeout
1018	NestedRetry	Warning	Warning	{Policy} is retrying a request that is already inside a retrying client.
1019	NestedRetryRepeat	Trace	Information	{Policy} is retrying inside another retrying client
1020	PolicyResolved	Debug	Information	{Policy} resolved: {Effective}
1021	PolicyClassifier	Trace	Debug	{Policy} classifier: {Rules}

Field names are shared with the metric tag vocabulary wherever both exist (Policy, Verdict, Reason), so a structured record and a metric describe the same call with the same words.

Events 1010, 1011, 1016 and 1018 are rate-limited per policy - see flood control. Events 1007, 1012, 1017 and 1019 are the quiet forms the suppressed occurrences take.