Deadlock tests

Libraries/Esiur/Protocol/DeadlockResolutionMode.cs

@@ -0,0 +1,31 @@
+namespace Esiur.Protocol;
+
+/// <summary>
+/// Strategy used by <c>EpConnection.FetchResource</c> when it is asked for a resource whose
+/// attachment is already in flight. Selectable mainly for experimental A/B/C evaluation of the
+/// deadlock-prevention algorithm.
+/// </summary>
+public enum DeadlockResolutionMode : byte
+{
+    /// <summary>
+    /// Default. Wait for the in-flight attachment to complete, except when a genuine wait-for cycle
+    /// is detected (same dependency chain, or a cross-chain cycle in the wait-for graph), in which
+    /// case a placeholder is returned to break it. Never deadlocks and never returns an unnecessary
+    /// placeholder.
+    /// </summary>
+    WaitWithCycleDetection = 0,
+
+    /// <summary>
+    /// Legacy behaviour: return the not-yet-attached placeholder to any cross-chain requester of an
+    /// in-flight resource. Never deadlocks, but delivers partially-attached resources for non-cyclic
+    /// contention (the bug under study).
+    /// </summary>
+    LegacyCrossChainPlaceholder = 1,
+
+    /// <summary>
+    /// No cycle handling at all: always wait for the in-flight attachment, even within the same
+    /// dependency chain. Genuinely deadlocks whenever the request graph contains a cycle. Used only
+    /// to demonstrate that cycle handling is necessary and that the deadlock detector works.
+    /// </summary>
+    NaiveWait = 2,
+}