Joseph Doherty
f920b4cbf5
Decrement was decrement-first with a single non-retried repair CAS. From zero, two unmatched decrements (SignalR calls OnDisconnectedAsync for a connection whose OnConnectedAsync faulted) capture -1 and -2; a real Increment then makes the count -1, and the first decrementer's stale CompareExchange(0, -1) matches and resets to zero — erasing a live connection, so the idle gate freezes an open dashboard. The same lost race also made Decrement report 0 when it had not written 0. Clamping now happens inside the compare-and-swap: read, clamp, publish, retry on loss. A lost race re-reads the fresh value instead of repairing a stale one. The counter moves to its own file per the one-public-type-per-file convention and gains direct tests: the zero floor under concurrent unmatched decrements, matched pairs settling at zero, and an interleaved connect/disconnect stress round. The stress test asserts the observable invariants only — the specific interleaving cannot be forced through the public API (verified: the previous implementation passes it), which its remarks now state rather than implying a reproducer. A hub wiring test is skipped for the EventsHub reason: driving Hub.OnConnectedAsync needs caller-clients and connection-context fakes, and the overrides are two lines of delegation to the tested type. Also documents that the API-key refresh's pre-gate time check races benignly.
42 lines
1.7 KiB
C#
42 lines
1.7 KiB
C#
using Microsoft.AspNetCore.Authorization;
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using Microsoft.AspNetCore.SignalR;
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namespace ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs;
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/// <summary>
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/// SignalR hub that pushes a fresh <see cref="DashboardSnapshot"/> on every
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/// snapshot refresh. New connections receive the current snapshot
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/// immediately via <see cref="OnConnectedAsync"/>; subsequent refreshes are
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/// broadcast by <see cref="DashboardSnapshotPublisher"/>.
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/// </summary>
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/// <remarks>
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/// Connections are counted into <see cref="DashboardSnapshotHubConnectionCounter"/>
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/// so <see cref="DashboardSnapshotPublisher"/> can stop building and broadcasting
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/// snapshots while nobody is watching.
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/// </remarks>
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[Authorize(Policy = DashboardAuthenticationDefaults.HubClientsPolicy)]
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public sealed class DashboardSnapshotHub(
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IDashboardSnapshotService snapshotService,
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DashboardSnapshotHubConnectionCounter connectionCounter) : Hub
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{
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/// <summary>Method name used to push snapshot updates to clients.</summary>
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public const string SnapshotMessage = "SnapshotUpdated";
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/// <inheritdoc />
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public override async Task OnConnectedAsync()
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{
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// Count the viewer before seeding it, so the publisher resumes its tick
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// no later than the first snapshot this connection renders.
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connectionCounter.Increment();
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await Clients.Caller.SendAsync(SnapshotMessage, snapshotService.GetSnapshot()).ConfigureAwait(false);
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await base.OnConnectedAsync().ConfigureAwait(false);
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}
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/// <inheritdoc />
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public override async Task OnDisconnectedAsync(Exception? exception)
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{
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connectionCounter.Decrement();
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await base.OnDisconnectedAsync(exception).ConfigureAwait(false);
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}
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}
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