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add custom hash function #29

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add custom hash function #29

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38 changes: 29 additions & 9 deletions consistent.go
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Original file line number Diff line number Diff line change
Expand Up @@ -48,22 +48,39 @@ type Consistent struct {
circle map[uint32]string
members map[string]bool
sortedHashes uints
NumberOfReplicas int
numberOfReplicas int
count int64
scratch [64]byte
UseFnv bool
customHashFunc func(string) uint32
once *sync.Once
sync.RWMutex
}

const _defaultNumofReplicas = 20

// New creates a new Consistent object with a default setting of 20 replicas for each entry.
//
// To change the number of replicas, set NumberOfReplicas before adding entries.
func New() *Consistent {
c := new(Consistent)
c.NumberOfReplicas = 20
c.circle = make(map[uint32]string)
c.members = make(map[string]bool)
return c
return &Consistent{
numberOfReplicas: _defaultNumofReplicas,
circle: make(map[uint32]string),
members: make(map[string]bool),
once: &sync.Once{},
}
}

// SetRepNum set the number of replicas
func (c *Consistent) SetRepNum(n int) {
c.once.Do(func() {
c.numberOfReplicas = n
})
}

// NumberOfReplicas return the number of replicas
func (c *Consistent) NumberOfReplicas() int {
return c.numberOfReplicas
}

// eltKey generates a string key for an element with an index.
Expand All @@ -81,7 +98,7 @@ func (c *Consistent) Add(elt string) {

// need c.Lock() before calling
func (c *Consistent) add(elt string) {
for i := 0; i < c.NumberOfReplicas; i++ {
for i := 0; i < c.numberOfReplicas; i++ {
c.circle[c.hashKey(c.eltKey(elt, i))] = elt
}
c.members[elt] = true
Expand All @@ -98,7 +115,7 @@ func (c *Consistent) Remove(elt string) {

// need c.Lock() before calling
func (c *Consistent) remove(elt string) {
for i := 0; i < c.NumberOfReplicas; i++ {
for i := 0; i < c.numberOfReplicas; i++ {
delete(c.circle, c.hashKey(c.eltKey(elt, i)))
}
delete(c.members, elt)
Expand Down Expand Up @@ -238,6 +255,9 @@ func (c *Consistent) GetN(name string, n int) ([]string, error) {
}

func (c *Consistent) hashKey(key string) uint32 {
if c.customHashFunc != nil {
return c.customHashFunc(key)
}
if c.UseFnv {
return c.hashKeyFnv(key)
}
Expand All @@ -262,7 +282,7 @@ func (c *Consistent) hashKeyFnv(key string) uint32 {
func (c *Consistent) updateSortedHashes() {
hashes := c.sortedHashes[:0]
//reallocate if we're holding on to too much (1/4th)
if cap(c.sortedHashes)/(c.NumberOfReplicas*4) > len(c.circle) {
if cap(c.sortedHashes)/(c.numberOfReplicas*4) > len(c.circle) {
hashes = nil
}
for k := range c.circle {
Expand Down
4 changes: 2 additions & 2 deletions consistent_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ func TestNew(t *testing.T) {
if x == nil {
t.Errorf("expected obj")
}
checkNum(x.NumberOfReplicas, 20, t)
checkNum(x.NumberOfReplicas(), 20, t)
}

func TestAdd(t *testing.T) {
Expand Down Expand Up @@ -689,7 +689,7 @@ func TestCollisionsCRC(t *testing.T) {
count := 0
for scanner.Scan() {
word := scanner.Text()
for i := 0; i < c.NumberOfReplicas; i++ {
for i := 0; i < c.NumberOfReplicas(); i++ {
ekey := c.eltKey(word, i)
// ekey := word + "|" + strconv.Itoa(i)
k := c.hashKey(ekey)
Expand Down