perf(worker): message-driven completion waits — the STA pumps continuously while waiting
This commit is contained in:
Joseph Doherty
@@ -4,6 +4,7 @@ using System.Threading;
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using Google.Protobuf.Collections;
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using Google.Protobuf.WellKnownTypes;
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using ZB.MOM.WW.MxGateway.Contracts.Proto;
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using ZB.MOM.WW.MxGateway.Worker.Sta;
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namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
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@@ -26,6 +27,18 @@ public sealed class MxAccessValueCache
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private readonly Dictionary<long, CachedValue> entries = new();
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private readonly object syncRoot = new();
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// Set by Set() so a waiter blocked in TryWaitForUpdate wakes the moment a
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// value lands instead of after the next blind poll tick. In the live worker
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// the value is recorded from inside the waiter's own pumpStep (COM
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// dispatches OnDataChange on the STA), so the message wake is what does the
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// work there; this handle covers the cross-thread producers — the tests, and
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// any future off-STA writer. Not IDisposable on purpose: the cache is
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// co-owned by MxAccessBaseEventSink and MxAccessSession with no single
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// teardown owner, and a late COM callback must never Set a disposed handle.
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// One kernel event per session (one session per worker process), released by
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// the handle's finalizer.
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private readonly AutoResetEvent updateSignal = new(false);
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/// <summary>Records a fresh OnDataChange payload for the given handle pair.</summary>
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/// <param name="serverHandle">MXAccess server handle.</param>
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/// <param name="itemHandle">MXAccess item handle.</param>
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@@ -68,6 +81,11 @@ public sealed class MxAccessValueCache
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cachedTimestamp,
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mxEvent.Statuses.Clone());
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}
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// Signaled outside the lock: the waiter re-takes syncRoot (through
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// TryGet) the instant it wakes, so signaling while holding it would hand
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// it guaranteed contention.
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updateSignal.Set();
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}
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/// <summary>Tries to read the most recent cached value for the handle pair.</summary>
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@@ -107,16 +125,28 @@ public sealed class MxAccessValueCache
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/// <summary>
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/// Waits until the cache entry's version exceeds <paramref name="sinceVersion"/>
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/// or the deadline elapses, calling <paramref name="pumpStep"/> on every poll
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/// or the deadline elapses, calling <paramref name="pumpStep"/> on every
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/// iteration so the worker's STA can dispatch the inbound MXAccess message.
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/// </summary>
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/// <remarks>
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/// The idle part of each iteration blocks in
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/// <see cref="StaWaitHelper.WaitForSignalOrMessages"/> rather than
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/// <c>Thread.Sleep</c>: a sleeping STA pumps no Windows messages, so a
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/// ReadBulk waiting on the first OnDataChange would only dispatch it at
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/// poll-tick granularity — and it holds the apartment for up to
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/// <c>timeout_ms</c> per tag, stalling every other COM event with it. The
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/// Win32 wait returns the instant a message needs pumping (or the value
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/// is recorded from another thread), so the apartment keeps dispatching
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/// continuously for the whole wait. The per-tag timeout, the deadline
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/// math, and both return shapes are unchanged.
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/// </remarks>
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/// <param name="serverHandle">MXAccess server handle.</param>
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/// <param name="itemHandle">MXAccess item handle.</param>
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/// <param name="sinceVersion">Version snapshot captured before the wait.</param>
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/// <param name="deadlineUtc">Absolute UTC deadline.</param>
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/// <param name="pumpStep">Action that pumps any pending Windows messages.</param>
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/// <param name="value">The cached value if the update was received before the deadline.</param>
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/// <param name="pollIntervalMs">How long to sleep between pump cycles. Default 5 ms.</param>
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/// <param name="pollIntervalMs">Upper bound on one idle wait slice — the cadence at which <paramref name="pumpStep"/> runs when nothing wakes the wait. Default 5 ms, itself capped at <see cref="StaWaitHelper.MaxFallbackTickMilliseconds"/>.</param>
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/// <returns><see langword="true"/> if an update newer than <paramref name="sinceVersion"/> arrived before the deadline; otherwise <see langword="false"/>.</returns>
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public bool TryWaitForUpdate(
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int serverHandle,
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@@ -134,6 +164,12 @@ public sealed class MxAccessValueCache
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while (true)
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{
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// Pumped unconditionally at the top of every iteration — including
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// the one that immediately follows a signaled wait, and the very
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// first before any waiting. Dispatching the message is what fills
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// the cache in the live worker, and unit tests stand in for the STA
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// by driving the cache from their fake pumpStep, so this call must
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// never be conditional on a real message queue.
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pumpStep();
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if (TryGet(serverHandle, itemHandle, out value) && value.Version > sinceVersion)
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@@ -141,12 +177,18 @@ public sealed class MxAccessValueCache
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return true;
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}
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if (DateTime.UtcNow >= deadlineUtc)
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// Same expiry test as the sleep-polled version: remaining <= zero is
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// exactly DateTime.UtcNow >= deadlineUtc. `value` keeps whatever the
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// TryGet above left in it on this path, as before.
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TimeSpan remaining = deadlineUtc - DateTime.UtcNow;
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if (remaining <= TimeSpan.Zero)
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{
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return false;
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}
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Thread.Sleep(pollIntervalMs);
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StaWaitHelper.WaitForSignalOrMessages(
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updateSignal,
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StaWaitHelper.ClampWaitMilliseconds(remaining, pollIntervalMs));
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}
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}
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@@ -3,6 +3,7 @@ using System.Collections.Generic;
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using System.Threading;
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using Google.Protobuf.Collections;
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using ZB.MOM.WW.MxGateway.Contracts.Proto;
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using ZB.MOM.WW.MxGateway.Worker.Sta;
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namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
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@@ -25,6 +26,18 @@ public sealed class MxAccessWriteCompletionCache
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private readonly Dictionary<long, CompletionEntry> entries = new();
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private readonly object syncRoot = new();
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// Set by Record so a waiter blocked in TryWaitForCompletion wakes the moment
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// a completion lands instead of after the next blind poll tick. In the live
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// worker the completion is recorded from inside the waiter's own pumpStep
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// (COM dispatches OnWriteComplete on the STA), so the message wake is what
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// does the work there; this handle covers the cross-thread producers — the
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// tests, and any future off-STA recorder. Not IDisposable on purpose: the
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// cache is co-owned by MxAccessBaseEventSink and MxAccessSession with no
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// single teardown owner, and a late COM callback must never Set a disposed
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// handle. One kernel event per session (one session per worker process),
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// released by the handle's finalizer.
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private readonly AutoResetEvent completionSignal = new(false);
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/// <summary>Records the status rows of a fresh OnWriteComplete callback for the given handle pair.</summary>
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/// <param name="serverHandle">MXAccess server handle.</param>
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/// <param name="itemHandle">MXAccess item handle.</param>
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@@ -47,6 +60,10 @@ public sealed class MxAccessWriteCompletionCache
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: 1UL;
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entries[key] = new CompletionEntry(version, statuses.Clone());
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}
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// Signaled outside the lock: the waiter re-takes syncRoot the instant it
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// wakes, so signaling while holding it would hand it guaranteed contention.
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completionSignal.Set();
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}
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/// <summary>Returns the current completion version for a handle pair, or 0 if none was recorded.</summary>
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@@ -66,19 +83,29 @@ public sealed class MxAccessWriteCompletionCache
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}
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/// <summary>
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/// Polls for a completion newer than <paramref name="sinceVersion"/> until it
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/// Waits for a completion newer than <paramref name="sinceVersion"/> until it
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/// arrives or the deadline elapses, calling <paramref name="pumpStep"/> on every
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/// poll iteration so the worker's STA can dispatch the inbound MXAccess
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/// iteration so the worker's STA can dispatch the inbound MXAccess
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/// OnWriteComplete message. Same loop shape as
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/// <see cref="MxAccessValueCache.TryWaitForUpdate"/>.
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/// </summary>
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/// <remarks>
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/// The idle part of each iteration blocks in
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/// <see cref="StaWaitHelper.WaitForSignalOrMessages"/> rather than
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/// <c>Thread.Sleep</c>: a sleeping STA pumps no Windows messages, so the
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/// inbound OnWriteComplete could only ever be dispatched at poll-tick
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/// granularity. The Win32 wait returns the instant a message needs
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/// pumping (or the completion is recorded from another thread), so the
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/// apartment keeps dispatching COM events continuously for the whole
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/// wait. Timeouts, deadline math, and both return shapes are unchanged.
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/// </remarks>
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/// <param name="serverHandle">MXAccess server handle.</param>
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/// <param name="itemHandle">MXAccess item handle.</param>
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/// <param name="sinceVersion">Version snapshot captured before the write COM call.</param>
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/// <param name="deadlineUtc">Absolute UTC deadline.</param>
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/// <param name="pumpStep">Action that pumps any pending Windows messages.</param>
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/// <param name="statuses">The recorded status rows if a completion arrived before the deadline; empty otherwise.</param>
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/// <param name="pollIntervalMs">How long to sleep between pump cycles. Default 5 ms.</param>
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/// <param name="pollIntervalMs">Upper bound on one idle wait slice — the cadence at which <paramref name="pumpStep"/> runs when nothing wakes the wait. Default 5 ms, itself capped at <see cref="StaWaitHelper.MaxFallbackTickMilliseconds"/>.</param>
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/// <returns><see langword="true"/> if a completion newer than <paramref name="sinceVersion"/> arrived before the deadline; otherwise <see langword="false"/>.</returns>
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public bool TryWaitForCompletion(
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int serverHandle,
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@@ -96,6 +123,12 @@ public sealed class MxAccessWriteCompletionCache
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while (true)
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{
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// Pumped unconditionally at the top of every iteration — including
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// the one that immediately follows a signaled wait, and the very
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// first before any waiting. Dispatching the message is what fills
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// the cache in the live worker, and unit tests stand in for the STA
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// by recording the completion from inside their fake pumpStep, so
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// this call must never be conditional on a real message queue.
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pumpStep();
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lock (syncRoot)
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@@ -108,13 +141,18 @@ public sealed class MxAccessWriteCompletionCache
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}
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}
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if (DateTime.UtcNow >= deadlineUtc)
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// Same expiry test as the sleep-polled version: remaining <= zero is
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// exactly DateTime.UtcNow >= deadlineUtc.
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TimeSpan remaining = deadlineUtc - DateTime.UtcNow;
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if (remaining <= TimeSpan.Zero)
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{
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statuses = new RepeatedField<MxStatusProxy>();
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return false;
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}
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Thread.Sleep(pollIntervalMs);
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StaWaitHelper.WaitForSignalOrMessages(
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completionSignal,
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StaWaitHelper.ClampWaitMilliseconds(remaining, pollIntervalMs));
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}
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}
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