DP44/enriched-partialglm/Common/DTS.Common.Core/EventManager.md

---
source_files:
  - Common/DTS.Common.Core/EventManager/EventManager.cs
generated_at: "2026-04-16T11:42:05.172295+00:00"
model: "zai-org/GLM-5-FP8"
schema_version: 1
sha256: "59cbfaadaa1e572f"
---

# Documentation: DTS.Common.Core.EventManager

## 1. Purpose
The `EventManager` class provides a static, global implementation of the Publish/Subscribe (Pub/Sub) pattern. It enables decoupled communication between system components, allowing publishers to emit events without knowledge of subscribers, and subscribers to react to events without direct coupling to publishers. Additionally, it provides a diagnostic infrastructure to monitor the event system's activity, such as tracking subscription counts and event publication flow.

## 2. Public Interface

### Delegates
*   **`SubscriberCallbackDelegate<in T>(T item)`**
    *   The signature required for methods subscribing to events.
    *   Constraint: `T` must be a reference type (`class`).
*   **`DiagnosticCallbackDelegate(EventDiagnosticType eventType, Type t, object eventData, string listener)`**
    *   The signature required for methods subscribing to diagnostic events regarding the EventManager's internal operations.

### Static Class: `EventManager`

#### Methods
*   **`void Publish(T eventData) where T : class`**
    *   Publishes an event of type `T` to all registered subscribers.
    *   Iterates through the subscriber list for type `T`. If a subscriber has an `EventFilter`, the filter is evaluated; the callback is invoked only if the filter returns `true`.
    *   If no subscribers exist for type `T`, the method returns immediately without throwing an exception.
*   **`void Subscribe(SubscriberCallbackDelegate listener) where T : class`**
    *   Registers a listener for event type `T` without a filter.
    *   Overload: `void Subscribe(SubscriberCallbackDelegate listener, Predicate eventFilter) where T : class`
    *   Registers a listener with a predicate filter. The callback will only be invoked if `eventFilter(eventData)` returns `true`.
*   **`void UnSubscribe(SubscriberCallbackDelegate listener) where T : class`**
    *   Removes a specific listener from the subscriber list for type `T`.
    *   Uses the `Callback` delegate equality to find and remove the matching `EventMetaData`.
*   **`void Clear()`**
    *   Removes all listeners for all event types from the `SubscriberList`.
*   **`void SubscribeToDiagnosticEvents(DiagnosticCallbackDelegate listener)`**
    *   Registers a listener to receive diagnostic events (e.g., when items are added or removed).
*   **`void UnSubscribeToDiagnosticEvents(DiagnosticCallbackDelegate listener)`**
    *   Removes a specific listener from the diagnostic events list.
*   **`void ClearDiagnosticEvents()`**
    *   Removes all listeners from the diagnostic events list.

### Enum: `EventDiagnosticType`
Defines the types of diagnostic events generated by the system.
*   `AddListener` (0)
*   `AddListenerDiagnostic` (1)
*   `PublishEvent` (2)
*   `RemoveListenerDiagnostic` (3)
*   `RemoveListener` (4)

## 3. Invariants
*   **Type Constraint:** All event types `T` used in `Publish`, `Subscribe`, and `UnSubscribe` must be reference types (`class`).
*   **Thread Safety:** The source code does not contain any locking mechanisms (e.g., `lock`, `Monitor`) around the static `Dictionary` or `List` collections. The module assumes a single-threaded execution context or requires external synchronization by the caller.
*   **Reference Equality:** Unsubscription relies on delegate reference equality. A subscriber must pass the exact same delegate instance used during `Subscribe` to successfully `UnSubscribe`.
*   **Internal Storage:** Listeners are stored internally as `EventMetaData` objects within a `List<object>`, despite the dictionary value type being `List<object>`.

## 4. Dependencies
*   **Internal Dependencies:**
    *   `System.Collections.Generic` (for `Dictionary`, `List`, `Predicate`)
    *   `System.Reflection` (for `MemberInfo`, `Type` used in diagnostics)
*   **External Dependencies:**
    *   None identified from the source file alone. As a core utility, it is likely widely depended upon by higher-level application modules.

## 5. Gotchas
*   **Thread Safety Risk:** The `SubscriberList` and `DiagnosticList` are static and mutable. Concurrent calls to `Subscribe`/`Publish` from different threads will cause race conditions and likely throw exceptions (e.g., `InvalidOperationException` on the list enumerator during `Publish`).
*   **Diagnostic "Clear" Behavior:** The `ClearDiagnosticEvents()` method clears the `DiagnosticList` *before* sending the final `RemoveListenerDiagnostic` event. Consequently, the final diagnostic event is sent to an empty list and will effectively be lost/ignored.
*   **Diagnostic Noise during Publish:** The `Publish` method sends a `PublishEvent` diagnostic message *inside* the loop for every single subscriber. If one event has 10 subscribers, 10 diagnostic events are fired for a single `Publish` call.
*   **Memory Leaks:** Because `SubscriberList` is static and holds references to delegate targets, failing to call `UnSubscribe` will prevent the subscriber objects from being garbage collected.
*   **Silent Failures:** `Publish` silently ignores the event if no subscribers are registered. `UnSubscribe` silently does nothing if the listener is not found.