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PrometheusExporter: New concurrency handling for scrape middleware + …
…http server (#2610) * PoC for coordinating prometheus pull threads. * Allocation free on .NET Core 3.1+ & locks are now tied to a specific exporter. * Use CollectionManager in HttpServer. Remove delegate allocation. * Bug fixes and benchmark updates. * Configurable cache duration & bug fixes. * Unit tests and bug fixes. * More interesting unit test. * Sealed PrometheusCollectionManager. * Nits. * CHANGELOG update. * Doc tweaks. * README update. Co-authored-by: Cijo Thomas <[email protected]>
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src/OpenTelemetry.Exporter.Prometheus/Implementation/PrometheusCollectionManager.cs
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|---|---|---|
| @@ -0,0 +1,216 @@ | ||
| // <copyright file="PrometheusCollectionManager.cs" company="OpenTelemetry Authors"> | ||
| // Copyright The OpenTelemetry Authors | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
| // </copyright> | ||
|
|
||
| using System; | ||
| using System.Runtime.CompilerServices; | ||
| using System.Threading; | ||
| using System.Threading.Tasks; | ||
| using OpenTelemetry.Metrics; | ||
|
|
||
| namespace OpenTelemetry.Exporter.Prometheus | ||
| { | ||
| internal sealed class PrometheusCollectionManager | ||
| { | ||
| private readonly PrometheusExporter exporter; | ||
| private readonly int scrapeResponseCacheDurationInMilliseconds; | ||
| private readonly Func<Batch<Metric>, ExportResult> onCollectRef; | ||
| private byte[] buffer = new byte[85000]; // encourage the object to live in LOH (large object heap) | ||
| private int globalLockState; | ||
| private ArraySegment<byte> previousDataView; | ||
| private DateTime? previousDataViewExpirationAtUtc; | ||
| private int readerCount; | ||
| private bool collectionRunning; | ||
| private TaskCompletionSource<ArraySegment<byte>> collectionTcs; | ||
|
|
||
| public PrometheusCollectionManager(PrometheusExporter exporter) | ||
| { | ||
| this.exporter = exporter; | ||
| this.scrapeResponseCacheDurationInMilliseconds = this.exporter.Options.ScrapeResponseCacheDurationMilliseconds; | ||
| this.onCollectRef = this.OnCollect; | ||
| } | ||
|
|
||
| #if NETCOREAPP3_1_OR_GREATER | ||
| public ValueTask<ArraySegment<byte>> EnterCollect() | ||
| #else | ||
| public Task<ArraySegment<byte>> EnterCollect() | ||
| #endif | ||
| { | ||
| this.EnterGlobalLock(); | ||
|
|
||
| // If we are within {ScrapeResponseCacheDurationMilliseconds} of the | ||
| // last successful collect, return the previous view. | ||
| if (this.previousDataViewExpirationAtUtc.HasValue && this.previousDataViewExpirationAtUtc >= DateTime.UtcNow) | ||
| { | ||
| Interlocked.Increment(ref this.readerCount); | ||
| this.ExitGlobalLock(); | ||
| #if NETCOREAPP3_1_OR_GREATER | ||
| return new ValueTask<ArraySegment<byte>>(this.previousDataView); | ||
| #else | ||
| return Task.FromResult(this.previousDataView); | ||
| #endif | ||
| } | ||
|
|
||
| // If a collection is already running, return a task to wait on the result. | ||
| if (this.collectionRunning) | ||
| { | ||
| if (this.collectionTcs == null) | ||
| { | ||
| this.collectionTcs = new TaskCompletionSource<ArraySegment<byte>>(TaskCreationOptions.RunContinuationsAsynchronously); | ||
| } | ||
|
|
||
| Interlocked.Increment(ref this.readerCount); | ||
| this.ExitGlobalLock(); | ||
| #if NETCOREAPP3_1_OR_GREATER | ||
| return new ValueTask<ArraySegment<byte>>(this.collectionTcs.Task); | ||
| #else | ||
| return this.collectionTcs.Task; | ||
| #endif | ||
| } | ||
|
|
||
| this.WaitForReadersToComplete(); | ||
|
|
||
| // Start a collection on the current thread. | ||
| this.collectionRunning = true; | ||
| this.previousDataViewExpirationAtUtc = null; | ||
| Interlocked.Increment(ref this.readerCount); | ||
| this.ExitGlobalLock(); | ||
|
|
||
| bool result = this.ExecuteCollect(); | ||
| if (result && this.scrapeResponseCacheDurationInMilliseconds > 0) | ||
| { | ||
| this.previousDataViewExpirationAtUtc = DateTime.UtcNow.AddMilliseconds(this.scrapeResponseCacheDurationInMilliseconds); | ||
| } | ||
|
|
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| this.EnterGlobalLock(); | ||
|
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| this.collectionRunning = false; | ||
|
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||
| if (this.collectionTcs != null) | ||
| { | ||
| this.collectionTcs.SetResult(this.previousDataView); | ||
| this.collectionTcs = null; | ||
| } | ||
|
|
||
| this.ExitGlobalLock(); | ||
|
|
||
| #if NETCOREAPP3_1_OR_GREATER | ||
| return new ValueTask<ArraySegment<byte>>(this.previousDataView); | ||
| #else | ||
| return Task.FromResult(this.previousDataView); | ||
| #endif | ||
| } | ||
|
|
||
| [MethodImpl(MethodImplOptions.AggressiveInlining)] | ||
| public void ExitCollect() | ||
| { | ||
| Interlocked.Decrement(ref this.readerCount); | ||
| } | ||
|
|
||
| [MethodImpl(MethodImplOptions.AggressiveInlining)] | ||
| private void EnterGlobalLock() | ||
| { | ||
| SpinWait lockWait = default; | ||
| while (true) | ||
| { | ||
| if (Interlocked.CompareExchange(ref this.globalLockState, 1, this.globalLockState) != 0) | ||
| { | ||
| lockWait.SpinOnce(); | ||
| continue; | ||
| } | ||
|
|
||
| break; | ||
| } | ||
| } | ||
|
|
||
| [MethodImpl(MethodImplOptions.AggressiveInlining)] | ||
| private void ExitGlobalLock() | ||
| { | ||
| this.globalLockState = 0; | ||
| } | ||
|
|
||
| [MethodImpl(MethodImplOptions.AggressiveInlining)] | ||
| private void WaitForReadersToComplete() | ||
| { | ||
| SpinWait readWait = default; | ||
| while (true) | ||
| { | ||
| if (Interlocked.CompareExchange(ref this.readerCount, 0, this.readerCount) != 0) | ||
| { | ||
| readWait.SpinOnce(); | ||
| continue; | ||
| } | ||
|
|
||
| break; | ||
| } | ||
| } | ||
|
|
||
| [MethodImpl(MethodImplOptions.AggressiveInlining)] | ||
| private bool ExecuteCollect() | ||
| { | ||
| this.exporter.OnExport = this.onCollectRef; | ||
| bool result = this.exporter.Collect(Timeout.Infinite); | ||
| this.exporter.OnExport = null; | ||
| return result; | ||
| } | ||
|
|
||
| private ExportResult OnCollect(Batch<Metric> metrics) | ||
| { | ||
| int cursor = 0; | ||
|
|
||
| try | ||
| { | ||
| foreach (var metric in metrics) | ||
| { | ||
| while (true) | ||
| { | ||
| try | ||
| { | ||
| cursor = PrometheusSerializer.WriteMetric(this.buffer, cursor, metric); | ||
| break; | ||
| } | ||
| catch (IndexOutOfRangeException) | ||
| { | ||
| int bufferSize = this.buffer.Length * 2; | ||
|
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||
| // there are two cases we might run into the following condition: | ||
| // 1. we have many metrics to be exported - in this case we probably want | ||
| // to put some upper limit and allow the user to configure it. | ||
| // 2. we got an IndexOutOfRangeException which was triggered by some other | ||
| // code instead of the buffer[cursor++] - in this case we should give up | ||
| // at certain point rather than allocating like crazy. | ||
| if (bufferSize > 100 * 1024 * 1024) | ||
| { | ||
| throw; | ||
| } | ||
|
|
||
| var newBuffer = new byte[bufferSize]; | ||
| this.buffer.CopyTo(newBuffer, 0); | ||
| this.buffer = newBuffer; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| this.previousDataView = new ArraySegment<byte>(this.buffer, 0, cursor); | ||
| return ExportResult.Success; | ||
| } | ||
| catch (Exception) | ||
| { | ||
| this.previousDataView = new ArraySegment<byte>(Array.Empty<byte>(), 0, 0); | ||
| return ExportResult.Failure; | ||
| } | ||
| } | ||
| } | ||
| } |
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