Deprecate old hashers since they're not safe for concurrency

In a concurrent environment, calling `Reset()` on the hasher risks
corrupting any ongoing usage of it.

Introduce a new set of helpers that returns a new instance of a hasher
instead and deprecate the old ones (but keep for backwards
compatibility).

README.md

@@ -20,13 +20,13 @@ func main() {
 Includes a helper function for using a `string` as key instead of an `uint64`. This requires a hasher that computes the string into a format accepted by `Hash()`. Such a hasher that uses [CRC-64 (ECMA)](https://en.wikipedia.org/wiki/Cyclic_redundancy_check) is also included for convenience.
 
 ```go
-h := jump.HashString("127.0.0.1", 8, jump.CRC64)  // h = 7
+h := jump.HashString("127.0.0.1", 8, jump.NewCRC64())  // h = 7
 ```
 
 In reality though you probably want to use a `Hasher` so you won't have to repeat the bucket size and which key hasher used. It also uses more convenient types, like `int` instead of `int32`.
 
 ```go
-hasher := jump.New(8, jump.CRC64)
+hasher := jump.New(8, jump.NewCRC64())
 h := hasher.Hash("127.0.0.1")  // h = 7
 ```
 

doc.go

@@ -1,4 +1,6 @@
 /*
+Package jump implements the "jump consistent hash" algorithm.
+
 Example
 
  h := jump.Hash(256, 1024)  // h = 520

jump.go

@@ -77,12 +77,19 @@ func (h *Hasher) Hash(key string) int {
 var (
 	// CRC32 uses the 32-bit Cyclic Redundancy Check (CRC-32) with the IEEE
 	// polynomial.
-	CRC32 hash.Hash64 = &crc32Hasher{crc32.NewIEEE()}
+	NewCRC32 func() hash.Hash64 = func() hash.Hash64 { return &crc32Hasher{crc32.NewIEEE()} }
 	// CRC64 uses the 64-bit Cyclic Redundancy Check (CRC-64) with the ECMA
 	// polynomial.
-	CRC64 hash.Hash64 = crc64.New(crc64.MakeTable(crc64.ECMA))
+	NewCRC64 func() hash.Hash64 = func() hash.Hash64 { return crc64.New(crc64.MakeTable(crc64.ECMA)) }
 	// FNV1 uses the non-cryptographic hash function FNV-1.
-	FNV1 hash.Hash64 = fnv.New64()
+	NewFNV1 func() hash.Hash64 = func() hash.Hash64 { return fnv.New64() }
 	// FNV1a uses the non-cryptographic hash function FNV-1a.
+	NewFNV1a func() hash.Hash64 = func() hash.Hash64 { return fnv.New64a() }
+
+	// These are deprecated because they're not safe for concurrent use. Please
+	// use the New* functions instead.
+	CRC32 hash.Hash64 = &crc32Hasher{crc32.NewIEEE()}
+	CRC64 hash.Hash64 = crc64.New(crc64.MakeTable(crc64.ECMA))
+	FNV1  hash.Hash64 = fnv.New64()
 	FNV1a hash.Hash64 = fnv.New64a()
 )

jump_test.go

@@ -35,19 +35,19 @@ func TestJumpHash(t *testing.T) {
 var jumpStringTestVectors = []struct {
 	key      string
 	buckets  int32
-	hasher   hash.Hash64
+	hasher   func() hash.Hash64
 	expected int32
 }{
-	{"localhost", 10, CRC32, 9},
-	{"ёлка", 10, CRC64, 6},
-	{"ветер", 10, FNV1, 3},
-	{"中国", 10, FNV1a, 5},
-	{"日本", 10, CRC64, 6},
+	{"localhost", 10, NewCRC32, 9},
+	{"ёлка", 10, NewCRC64, 6},
+	{"ветер", 10, NewFNV1, 3},
+	{"中国", 10, NewFNV1a, 5},
+	{"日本", 10, NewCRC64, 6},
 }
 
 func TestJumpHashString(t *testing.T) {
 	for _, v := range jumpStringTestVectors {
-		h := HashString(v.key, v.buckets, v.hasher)
+		h := HashString(v.key, v.buckets, v.hasher())
 		if h != v.expected {
 			t.Errorf("expected bucket for key=%s to be %d, got %d",
 				strconv.Quote(v.key), v.expected, h)
@@ -57,7 +57,7 @@ func TestJumpHashString(t *testing.T) {
 
 func TestHasher(t *testing.T) {
 	for _, v := range jumpStringTestVectors {
-		hasher := New(int(v.buckets), v.hasher)
+		hasher := New(int(v.buckets), v.hasher())
 		h := hasher.Hash(v.key)
 		if int32(h) != v.expected {
 			t.Errorf("expected bucket for key=%s to be %d, got %d",
@@ -72,7 +72,7 @@ func ExampleHash() {
 }
 
 func ExampleHashString() {
-	fmt.Print(HashString("127.0.0.1", 8, CRC64))
+	fmt.Print(HashString("127.0.0.1", 8, NewCRC64()))
 	// Output: 7
 }
 
@@ -85,27 +85,27 @@ func BenchmarkHash(b *testing.B) {
 func BenchmarkHashStringCRC32(b *testing.B) {
 	s := "Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat."
 	for i := 0; i < b.N; i++ {
-		HashString(s, int32(i), CRC32)
+		HashString(s, int32(i), NewCRC32())
 	}
 }
 
 func BenchmarkHashStringCRC64(b *testing.B) {
 	s := "Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat."
 	for i := 0; i < b.N; i++ {
-		HashString(s, int32(i), CRC64)
+		HashString(s, int32(i), NewCRC64())
 	}
 }
 
 func BenchmarkHashStringFNV1(b *testing.B) {
 	s := "Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat."
 	for i := 0; i < b.N; i++ {
-		HashString(s, int32(i), FNV1)
+		HashString(s, int32(i), NewFNV1())
 	}
 }
 
 func BenchmarkHashStringFNV1a(b *testing.B) {
 	s := "Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat."
 	for i := 0; i < b.N; i++ {
-		HashString(s, int32(i), FNV1a)
+		HashString(s, int32(i), NewFNV1a())
 	}
 }