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fix Metric livelock by replacing potential infinate loop in MetricValuesBuffer.GetAndResetValue #2612

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merged 10 commits into from
Jun 17, 2022
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fix Metric livelock by replacing potential infinate loop in MetricValuesBuffer.GetAndResetValue #2612

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TimothyMothra Jun 15, 2022
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less invasive change
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Merge branch 'main' into tilee/1186_GetAndResetValue
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Update CHANGELOG.md
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13 changes: 12 additions & 1 deletion BASE/src/Microsoft.ApplicationInsights/Metrics/Extensibility/MetricValuesBuffer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,8 @@ public int NextFlushIndex
set { this.nextFlushIndex = value; }
}

protected abstract TValue InvalidValue { get; }

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public int IncWriteIndex()
{
Expand Down Expand Up @@ -91,13 +93,18 @@ public TValue GetAndResetValue(int index)
while (this.IsInvalidValue(value))
{
spinWait.SpinOnce();

if (spinWait.Count % 100 == 0)
{
// In tests (including stress tests) we always finished wating before 100 cycles.
// However, this is a protection against en extreme case on a slow machine.
Task.Delay(10).ConfigureAwait(continueOnCapturedContext: false).GetAwaiter().GetResult();
}
else if (spinWait.Count > 10000)
{
// exceeded maximum spin count. Break out to avoid infinite loop.
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return this.InvalidValue;
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}

value = this.GetAndResetValueOnce(this.values, index);
}
Expand Down Expand Up @@ -127,6 +134,8 @@ public MetricValuesBuffer_Double(int capacity)
{
}

protected override double InvalidValue => double.NaN;

[MethodImpl(MethodImplOptions.AggressiveInlining)]
protected override bool IsInvalidValue(double value)
{
Expand Down Expand Up @@ -162,6 +171,8 @@ public MetricValuesBuffer_Object(int capacity)
{
}

protected override object InvalidValue => null;

[MethodImpl(MethodImplOptions.AggressiveInlining)]
protected override bool IsInvalidValue(object value)
{
Expand Down