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Make the NewX() monitoring variables safe to re-register (#83)
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* make it safe to re-register monitoring variables

* try to fix CI
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fearful-symmetry authored Oct 11, 2022
1 parent 0b465c5 commit bce6efb
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Showing 2 changed files with 124 additions and 14 deletions.
91 changes: 77 additions & 14 deletions monitoring/metrics.go
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ package monitoring
import (
"encoding/json"
"expvar"
"fmt"
"math"
"strconv"
"sync"
Expand All @@ -43,8 +44,14 @@ type Int struct{ i atomic.Int64 }
// variable will be available via expvars package as well, but can not be removed
// anymore.
func NewInt(r *Registry, name string, opts ...Option) *Int {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*Int)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as Int", name, existingVar))
}
}

v := &Int{}
Expand All @@ -71,8 +78,14 @@ type Uint struct{ u atomic.Uint64 }
// variable will be available via expvars package as well, but can not be removed
// anymore.
func NewUint(r *Registry, name string, opts ...Option) *Uint {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*Uint)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as Uint", name, existingVar))
}
}

v := &Uint{}
Expand Down Expand Up @@ -102,8 +115,14 @@ type Float struct{ f atomic.Uint64 }
// variable will be available via expvars package as well, but can not be removed
// anymore.
func NewFloat(r *Registry, name string, opts ...Option) *Float {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*Float)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as Float", name, existingVar))
}
}

v := &Float{}
Expand Down Expand Up @@ -137,8 +156,14 @@ type Bool struct{ f atomic.Bool }
// variable will be available via expvars package as well, but can not be removed
// anymore.
func NewBool(r *Registry, name string, opts ...Option) *Bool {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*Bool)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as Bool", name, existingVar))
}
}

v := &Bool{}
Expand All @@ -164,8 +189,14 @@ type String struct {
// variable will be available via expvars package as well, but can not be removed
// anymore.
func NewString(r *Registry, name string, opts ...Option) *String {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*String)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as String", name, existingVar))
}
}

v := &String{}
Expand Down Expand Up @@ -209,8 +240,14 @@ type Func struct {
}

func NewFunc(r *Registry, name string, f func(Mode, Visitor), opts ...Option) *Func {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*Func)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as Func", name, existingVar))
}
}

v := &Func{f}
Expand Down Expand Up @@ -246,8 +283,14 @@ type Timestamp struct {

// NewTimestamp creates and registers a new timestamp variable.
func NewTimestamp(r *Registry, name string, opts ...Option) *Timestamp {
if r == nil {
r = Default
existingVar, r := setupMetric(r, name, opts)
if existingVar != nil {
cast, ok := existingVar.(*Timestamp)
if ok {
return cast
} else {
panicErr(fmt.Errorf("variable name %s was first registered as a %T, tried to register as Timestamp", name, existingVar))
}
}

v := &Timestamp{}
Expand Down Expand Up @@ -290,3 +333,23 @@ func (v *Timestamp) toString() string {
}
return v.cached
}

func setupMetric(reg *Registry, name string, opts []Option) (Var, *Registry) {
if reg == nil {
return nil, Default
}
vis := reg.Get(name)
if vis == nil {
return nil, reg
}

// Just being overly cautious.
// If someone tries to re-register a variable with options, should we try to "reset"
// the variable somehow? Even if we did, this wouldn't work 100% of the time, as we can't
// un-publish to expvar.
if len(opts) > 0 {
panicErr(fmt.Errorf("the variable %s cannot be re-registered with options", name))
}
return vis, reg

}
47 changes: 47 additions & 0 deletions monitoring/metrics_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,47 @@
// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you 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.

package monitoring

import (
"testing"

"github.com/stretchr/testify/require"
)

func TestSafeVars(t *testing.T) {
uintValName := "testUint"
testReg := Default.NewRegistry("safe_registry")
testUint := NewUint(testReg, uintValName)
testUint.Set(5)
// Add the first time
require.NotNil(t, testUint)

// Add the metric a second time
testSecondUint := NewUint(testReg, uintValName)
require.NotNil(t, testSecondUint)
// make sure we fetch the same unit
require.Equal(t, uint64(5), testSecondUint.Get())
}

func TestNilReg(t *testing.T) {
uintValName := "testUint"
// This can also just panic if there's a bug
testUint := NewUint(nil, uintValName)
require.NotNil(t, testUint)

}

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