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feat(sessions): multi-subscriber cap enforcement + mode-gated FailFast

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This commit is contained in:
Joseph Doherty
2026-06-15 15:32:08 -04:00
parent 7b12eebbd1
commit ac42783e36
12 changed files with 399 additions and 81 deletions
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src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/SessionEventDistributorTests.cs
+61 -12
View File
@@ -355,7 +355,8 @@ public sealed class SessionEventDistributorTests
Interlocked.Increment(ref overflowCalls);
Volatile.Write(ref observedIsOnlySubscriberValue, isOnlySubscriber);
Volatile.Write(ref observedIsOnlySubscriberSet, 1);
});
},
singleSubscriberMode: false);
await distributor.StartAsync(CancellationToken.None);
// Slow subscriber: registered but never read, so its capacity-2 channel fills.
@@ -377,7 +378,7 @@ public sealed class SessionEventDistributorTests
async () => await DrainUntilFaultAsync(slow.Reader));
Assert.Equal(SessionManagerErrorCode.EventQueueOverflow, fault.ErrorCode);
// Two subscribers were registered at overflow time, so isOnlySubscriber is false.
// Multi-subscriber mode, so isOnlySubscriber is always false (Task 8 mode-gating).
// Use Interlocked.Read / Volatile.Read so the test-thread reads are ordered after the
// pump-thread writes, avoiding a data race by the C# memory model.
Assert.Equal(1, Volatile.Read(ref overflowCalls));
@@ -395,15 +396,12 @@ public sealed class SessionEventDistributorTests
public async Task SlowSubscriberOverflow_WithMultipleSubscribers_HandlerSeesIsOnlySubscriberFalse_OtherKeepsReceiving()
{
// Distributor-level pin for "FailFast with multiple subscribers degrades to
// disconnect-only (no session fault)": when the overflowing subscriber is NOT the
// sole subscriber, isOnlySubscriber is false, so a FailFast-wired handler must NOT
// fault the session. This test drives the distributor directly (without GatewaySession)
// with two subscribers and a FailFast-style overflow handler seam, overflows the slow
// one, and asserts (a) isOnlySubscriber==false, (b) the other subscriber keeps
// receiving, and (c) the pump keeps running — all without a GatewaySession.
//
// TODO(Task 8): add a GatewaySession-level "session stays Ready" assertion once
// multi-subscriber config is enabled by the Tasks 7/8 validator/guard change.
// disconnect-only (no session fault)": in multi-subscriber mode isOnlySubscriber is
// always false (Task 8 mode-gating), so a FailFast-wired handler must NOT fault the
// session. This test drives the distributor directly (without GatewaySession) in
// multi-subscriber mode with two subscribers and a FailFast-style overflow handler
// seam, overflows the slow one, and asserts (a) isOnlySubscriber==false, (b) the other
// subscriber keeps receiving, and (c) the pump keeps running.
Channel<MxEvent> source = Channel.CreateUnbounded<MxEvent>();
bool handlerFiredWithFalse = false;
bool sessionFaultWouldBeCalled = false; // tracks if a FailFast path would fault
@@ -427,7 +425,8 @@ public sealed class SessionEventDistributorTests
// Single-subscriber: FailFast would fault the session — must not happen here.
Volatile.Write(ref sessionFaultWouldBeCalled, true);
}
});
},
singleSubscriberMode: false);
await distributor.StartAsync(CancellationToken.None);
// Slow subscriber: never reads, so capacity-2 channel overflows quickly.
@@ -520,6 +519,56 @@ public sealed class SessionEventDistributorTests
"isInternal must be true for a subscriber registered with isInternal: true.");
}
[Fact]
public async Task SingleSubscriberMode_LoneExternalOverflow_HandlerSeesIsOnlySubscriberTrue()
{
// Task 8 mode-gating: in single-subscriber mode a lone external subscriber that
// overflows reports isOnlySubscriber==true, so the legacy FailFast session-fault path
// is preserved. The decision is gated on the fixed session mode, NOT a live count, so
// it is race-free.
Channel<MxEvent> source = Channel.CreateUnbounded<MxEvent>();
int observedSet = 0;
bool observedValue = false;
await using SessionEventDistributor distributor = new(
"session-single-sub",
ct => source.Reader.ReadAllAsync(ct),
subscriberQueueCapacity: 2,
replayBufferCapacity: 0,
replayRetentionSeconds: 0,
NullLogger<SessionEventDistributor>.Instance,
TimeProvider.System,
(isOnlySubscriber, _) =>
{
Volatile.Write(ref observedValue, isOnlySubscriber);
Volatile.Write(ref observedSet, 1);
},
singleSubscriberMode: true);
await distributor.StartAsync(CancellationToken.None);
using IEventSubscriberLease external = distributor.Register();
for (ulong sequence = 1; sequence <= 10; sequence++)
{
source.Writer.TryWrite(Event(sequence));
}
SessionManagerException fault = await Assert.ThrowsAsync<SessionManagerException>(
async () => await DrainUntilFaultAsync(external.Reader));
Assert.Equal(SessionManagerErrorCode.EventQueueOverflow, fault.ErrorCode);
await Task.Run(async () =>
{
using CancellationTokenSource cts = new(ReadTimeout);
while (Volatile.Read(ref observedSet) == 0)
{
await Task.Delay(10, cts.Token);
}
});
Assert.True(Volatile.Read(ref observedValue),
"isOnlySubscriber must be true for a lone external subscriber in single-subscriber mode.");
}
private static async Task DrainUntilFaultAsync(ChannelReader<MxEvent> reader)
{
// Drains any buffered events, then surfaces the channel's completion fault (if any)