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fix: use a rwlock to avoid concurrent map read and write #210

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tim-mwangi merged 1 commit into from
Feb 24, 2023
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fix: use a rwlock to avoid concurrent map read and write #210

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7 changes: 7 additions & 0 deletions instrumentation/opentelemetry/metrics.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ package opentelemetry // import "github.com/hypertrace/goagent/instrumentation/o

import (
"net/http"
"sync"

"github.com/hypertrace/goagent/sdk"
"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
Expand All @@ -23,6 +24,7 @@ const (
type HttpOperationMetricsHandler struct {
operationNameGetter func(*http.Request) string
counters map[string]instrument.Int64Counter
countersMutex sync.RWMutex
}

var _ sdk.HttpOperationMetricsHandler = (*HttpOperationMetricsHandler)(nil)
Expand All @@ -44,6 +46,8 @@ func (mh *HttpOperationMetricsHandler) CreateRequestCount() {
otel.Handle(err)
}

mh.countersMutex.Lock()
defer mh.countersMutex.Unlock()
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@ryanericson ryanericson Feb 24, 2023

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So we think AddToRequestCount is racing with CreateRequestCount? But if I look at the code it looks like CreateRequestCount would have had to happen first as part init of WrapHandler?

Also we don't really need a map here right? Because we have a static set of metrics and can precreate counters?

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@tim-mwangi tim-mwangi Feb 24, 2023

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This made me think about how this is designed and I agree with you. I need to maybe get rid of the map and switch to static counters. I had a map because I thought there would be more counters we would add but we do not need a map if we can reference the counters directly.

mh.counters[RequestCount] = requestCountCounter
}

Expand All @@ -53,5 +57,8 @@ func (mh *HttpOperationMetricsHandler) AddToRequestCount(n int64, r *http.Reques
labeler, _ := otelhttp.LabelerFromContext(ctx)
operationName := mh.operationNameGetter(r)
attributes := append(labeler.Get(), semconv.HTTPServerMetricAttributesFromHTTPRequest(operationName, r)...)

mh.countersMutex.RLock()
defer mh.countersMutex.RUnlock()
mh.counters[RequestCount].Add(ctx, n, attributes...)
}