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Fix memory leak when tracing is enabled #3432

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Merged
jamescrosswell merged 3 commits into from
Jun 18, 2024
Merged

Fix memory leak when tracing is enabled #3432

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25ac033
Fix memory leak when tracing is enabled
jamescrosswell Jun 18, 2024
b33c944
Update CHANGELOG.md
jamescrosswell Jun 18, 2024
9ac327c
Update SentryTransactionTests.cs
jamescrosswell Jun 18, 2024
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
- Fixed Monitor duration calculation ([#3420]https://github.com/getsentry/sentry-dotnet/pull/3420)
- Fixed null IServiceProvider in anonymous routes with OpenTelemetry ([#3401](https://github.com/getsentry/sentry-dotnet/pull/3401))
- Fixed Trim warnings in Sentry.DiagnosticSource and WinUIUnhandledException integrations ([#3410](https://github.com/getsentry/sentry-dotnet/pull/3410))
- Fix memory leak when tracing is enabled ([#3432](https://github.com/getsentry/sentry-dotnet/pull/3432))

### Dependencies

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25 changes: 25 additions & 0 deletions src/Sentry/TransactionTracer.cs
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Expand Up @@ -167,7 +167,11 @@ public IReadOnlyList<string> Fingerprint
/// <inheritdoc />
public IReadOnlyDictionary<string, string> Tags => _tags;

#if NETSTANDARD2_1_OR_GREATER
private readonly ConcurrentBag<ISpan> _spans = new();
#else
private ConcurrentBag<ISpan> _spans = new();
#endif

/// <inheritdoc />
public IReadOnlyCollection<ISpan> Spans => _spans;
Expand Down Expand Up @@ -337,6 +341,14 @@ public void Push(ISpan span)
return null;
}
}

public void Clear()
{
lock (_lock)
{
TrackedSpans.Clear();
}
}
}
private readonly LastActiveSpanTracker _activeSpanTracker = new LastActiveSpanTracker();

Expand Down Expand Up @@ -373,6 +385,9 @@ public void Finish()

// Client decides whether to discard this transaction based on sampling
_hub.CaptureTransaction(new SentryTransaction(this));

// Release tracked spans
ReleaseSpans();
Comment on lines +389 to +390
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@bitsandfoxes bitsandfoxes Jun 18, 2024

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Do you know why this is required? Is something holding the reference to the TransactionTracer? Does that reference need to be released too?

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@jamescrosswell jamescrosswell Jun 18, 2024 •
edited
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I'm not sure I fully understand yet, no. The stack overflow thread linked above seems to imply ConcurrentBag<T> stores stuff in a thread local and leaves it there, unless you remove it. It seems improbable that we wouldn't have picked up on something so obvious years ago if that was the case though. That would mean massive memory leaks all over our SDK (we use ConcurrentBag<T> in a number of places).

I'll merge this PR, create a release, and then do a bit more digging on potentially replacing ConcurrentBag<T> with a light weight custom type that isn't so mysterious. That will require some benchmarking and testing though, as it would be replacing something quite foundational.

}

/// <inheritdoc />
Expand All @@ -395,4 +410,14 @@ public void Finish(Exception exception) =>

/// <inheritdoc />
public SentryTraceHeader GetTraceHeader() => new(TraceId, SpanId, IsSampled);

private void ReleaseSpans()
{
#if NETSTANDARD2_1_OR_GREATER
_spans.Clear();
#else
_spans = new ConcurrentBag<ISpan>();
#endif
_activeSpanTracker.Clear();
}
}
3 changes: 2 additions & 1 deletion test/Sentry.Tests/Protocol/SentryTransactionTests.cs
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Expand Up @@ -130,7 +130,8 @@ public void Redact_Redacts_Urls()
child2.SetExtra("f222", "p111");
child2.Finish(SpanStatus.OutOfRange);

txTracer.Finish(SpanStatus.Aborted);
// Don't finish the tracer - that would cause the spans to be released
// txTracer.Finish(SpanStatus.Aborted);

// Act
var transaction = new SentryTransaction(txTracer);
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